text: /*
   * Copyright 2015-2020 Leonid Yuriev <leo@yuriev.ru>
   * and other libmdbx authors: please see AUTHORS file.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted only as authorized by the OpenLDAP
   * Public License.
   *
   * A copy of this license is available in the file LICENSE in the
   * top-level directory of the distribution or, alternatively, at
   * <http://www.OpenLDAP.org/license.html>. */
  
  #define MDBX_ALLOY 1n#define MDBX_BUILD_SOURCERY 9854b516cd42bd97a2447d2f4adfda8cd99464906b15a3646a1409c129fbb1bc_v0_9_2_21_g1c70814
  #ifdef MDBX_CONFIG_H
  #include MDBX_CONFIG_H
  #endif
  
  #define LIBMDBX_INTERNALS
  #ifdef MDBX_TOOLS
  #define MDBX_DEPRECATED
  #endif /* MDBX_TOOLS */
  
  /* *INDENT-OFF* */
  /* clang-format off */
  
  /* In case the MDBX_DEBUG is undefined set it corresponding to NDEBUG */
  #ifndef MDBX_DEBUG
  #   ifdef NDEBUG
  #       define MDBX_DEBUG 0
  #   else
  #       define MDBX_DEBUG 1
  #   endif
  #endif
  
  /* Undefine the NDEBUG if debugging is enforced by MDBX_DEBUG */
  #if MDBX_DEBUG
  #   undef NDEBUG
  #endif
  
  #ifdef MDBX_ALLOY
  /* Amalgamated build */
  #   define MDBX_INTERNAL_FUNC static
  #   define MDBX_INTERNAL_VAR static
  #else
  /* Non-amalgamated build */
  #   define MDBX_INTERNAL_FUNC
  #   define MDBX_INTERNAL_VAR extern
  #endif /* MDBX_ALLOY */
  
  #ifndef MDBX_DISABLE_GNU_SOURCE
  #define MDBX_DISABLE_GNU_SOURCE 0
  #endif
  #if MDBX_DISABLE_GNU_SOURCE
  #undef _GNU_SOURCE
  #elif (defined(__linux__) || defined(__gnu_linux__)) && !defined(_GNU_SOURCE)
  #define _GNU_SOURCE
  #endif
  
  /*----------------------------------------------------------------------------*/
  
  /* Should be defined before any includes */
  #ifndef _FILE_OFFSET_BITS
  #   define _FILE_OFFSET_BITS 64
  #endif
  
  #ifdef __APPLE__
  #define _DARWIN_C_SOURCE
  #endif
  
  #ifdef _MSC_VER
  #   if _MSC_FULL_VER < 190024234
          /* Actually libmdbx was not tested with compilers older than 19.00.24234 (Visual Studio 2015 Update 3).
           * But you could remove this #error and try to continue at your own risk.
           * In such case please don't rise up an issues related ONLY to old compilers.
           */
  #       error "At least \"Microsoft C/C++ Compiler\" version 19.00.24234 (Visual Studio 2015 Update 3) is required."
  #   endif
  #   ifndef _CRT_SECURE_NO_WARNINGS
  #       define _CRT_SECURE_NO_WARNINGS
  #   endif
  #if _MSC_VER > 1800
  #   pragma warning(disable : 4464) /* relative include path contains '..' */
  #endif
  #if _MSC_VER > 1913
  #   pragma warning(disable : 5045) /* Compiler will insert Spectre mitigation... */
  #endif
  #pragma warning(disable : 4710) /* 'xyz': function not inlined */
  #pragma warning(disable : 4711) /* function 'xyz' selected for automatic inline expansion */
  #pragma warning(disable : 4201) /* nonstandard extension used : nameless struct / union */
  #pragma warning(disable : 4702) /* unreachable code */
  #pragma warning(disable : 4706) /* assignment within conditional expression */
  #pragma warning(disable : 4127) /* conditional expression is constant */
  #pragma warning(disable : 4324) /* 'xyz': structure was padded due to alignment specifier */
  #pragma warning(disable : 4310) /* cast truncates constant value */
  #pragma warning(disable : 4820) /* bytes padding added after data member for alignment */
  #pragma warning(disable : 4548) /* expression before comma has no effect; expected expression with side - effect */
  #pragma warning(disable : 4366) /* the result of the unary '&' operator may be unaligned */
  #pragma warning(disable : 4200) /* nonstandard extension used: zero-sized array in struct/union */
  #pragma warning(disable : 4204) /* nonstandard extension used: non-constant aggregate initializer */
  #pragma warning(disable : 4505) /* unreferenced local function has been removed */
  #endif                          /* _MSC_VER (warnings) */
  
  #include "mdbx.h"
  /*
   * Copyright 2015-2020 Leonid Yuriev <leo@yuriev.ru>
   * and other libmdbx authors: please see AUTHORS file.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted only as authorized by the OpenLDAP
   * Public License.
   *
   * A copy of this license is available in the file LICENSE in the
   * top-level directory of the distribution or, alternatively, at
   * <http://www.OpenLDAP.org/license.html>.
   */
  
  /* *INDENT-OFF* */
  /* clang-format off */
  
  #ifndef __GNUC_PREREQ
  #   if defined(__GNUC__) && defined(__GNUC_MINOR__)
  #       define __GNUC_PREREQ(maj, min) \
            ((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
  #   else
  #       define __GNUC_PREREQ(maj, min) (0)
  #   endif
  #endif /* __GNUC_PREREQ */
  
  #ifndef __CLANG_PREREQ
  #   ifdef __clang__
  #       define __CLANG_PREREQ(maj,min) \
            ((__clang_major__ << 16) + __clang_minor__ >= ((maj) << 16) + (min))
  #   else
  #       define __CLANG_PREREQ(maj,min) (0)
  #   endif
  #endif /* __CLANG_PREREQ */
  
  #ifndef __GLIBC_PREREQ
  #   if defined(__GLIBC__) && defined(__GLIBC_MINOR__)
  #       define __GLIBC_PREREQ(maj, min) \
            ((__GLIBC__ << 16) + __GLIBC_MINOR__ >= ((maj) << 16) + (min))
  #   else
  #       define __GLIBC_PREREQ(maj, min) (0)
  #   endif
  #endif /* __GLIBC_PREREQ */
  
  #ifndef __has_warning
  #   define __has_warning(x) (0)
  #endif
  
  #ifndef __has_include
  #   define __has_include(x) (0)
  #endif
  
  #if __has_feature(thread_sanitizer)
  #   define __SANITIZE_THREAD__ 1
  #endif
  
  #if __has_feature(address_sanitizer)
  #   define __SANITIZE_ADDRESS__ 1
  #endif
  
  /*----------------------------------------------------------------------------*/
  
  #ifndef __extern_C
  #   ifdef __cplusplus
  #       define __extern_C extern "C"
  #   else
  #       define __extern_C
  #   endif
  #endif /* __extern_C */
  
  #if !defined(nullptr) && !defined(__cplusplus) || (__cplusplus < 201103L && !defined(_MSC_VER))
  #   define nullptr NULL
  #endif
  
  /*----------------------------------------------------------------------------*/
  
  #ifndef __always_inline
  #   if defined(__GNUC__) || __has_attribute(__always_inline__)
  #       define __always_inline __inline __attribute__((__always_inline__))
  #   elif defined(_MSC_VER)
  #       define __always_inline __forceinline
  #   else
  #       define __always_inline
  #   endif
  #endif /* __always_inline */
  
  #ifndef __noinline
  #   if defined(__GNUC__) || __has_attribute(__noinline__)
  #       define __noinline __attribute__((__noinline__))
  #   elif defined(_MSC_VER)
  #       define __noinline __declspec(noinline)
  #   else
  #       define __noinline
  #   endif
  #endif /* __noinline */
  
  #ifndef __must_check_result
  #   if defined(__GNUC__) || __has_attribute(__warn_unused_result__)
  #       define __must_check_result __attribute__((__warn_unused_result__))
  #   else
  #       define __must_check_result
  #   endif
  #endif /* __must_check_result */
  
  #ifndef __maybe_unused
  #   if defined(__GNUC__) || __has_attribute(__unused__)
  #       define __maybe_unused __attribute__((__unused__))
  #   else
  #       define __maybe_unused
  #   endif
  #endif /* __maybe_unused */
  
  #if !defined(__noop) && !defined(_MSC_VER)
  #   define __noop(...) do {} while(0)
  #endif /* __noop */
  
  #ifndef __fallthrough
  #  if defined(__cplusplus) && (__has_cpp_attribute(fallthrough) &&             \
       (!defined(__clang__) || __clang__ > 4)) || __cplusplus >= 201703L
  #    define __fallthrough [[fallthrough]]
  #  elif __GNUC_PREREQ(8, 0) && defined(__cplusplus) && __cplusplus >= 201103L
  #    define __fallthrough [[fallthrough]]
  #  elif __GNUC_PREREQ(7, 0) &&                                                 \
      (!defined(__LCC__) || (__LCC__ == 124 && __LCC_MINOR__ >= 12) ||           \
       (__LCC__ == 125 && __LCC_MINOR__ >= 5) || (__LCC__ >= 126))
  #    define __fallthrough __attribute__((__fallthrough__))
  #  elif defined(__clang__) && defined(__cplusplus) && __cplusplus >= 201103L &&\
      __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough")
  #    define __fallthrough [[clang::fallthrough]]
  #  else
  #    define __fallthrough
  #  endif
  #endif /* __fallthrough */
  
  #ifndef __unreachable
  #   if __GNUC_PREREQ(4,5) || __has_builtin(__builtin_unreachable)
  #       define __unreachable() __builtin_unreachable()
  #   elif defined(_MSC_VER)
  #       define __unreachable() __assume(0)
  #   else
  #       define __unreachable() __noop()
  #   endif
  #endif /* __unreachable */
  
  #ifndef __prefetch
  #   if defined(__GNUC__) || defined(__clang__) || __has_builtin(__builtin_prefetch)
  #       define __prefetch(ptr) __builtin_prefetch(ptr)
  #   else
  #       define __prefetch(ptr) __noop(ptr)
  #   endif
  #endif /* __prefetch */
  
  #ifndef __nothrow
  #   if defined(__cplusplus)
  #       if __cplusplus < 201703L
  #           define __nothrow throw()
  #       else
  #           define __nothrow noexcept(true)
  #       endif /* __cplusplus */
  #   elif defined(__GNUC__) || __has_attribute(__nothrow__)
  #       define __nothrow __attribute__((__nothrow__))
  #   elif defined(_MSC_VER) && defined(__cplusplus)
  #       define __nothrow __declspec(nothrow)
  #   else
  #       define __nothrow
  #   endif
  #endif /* __nothrow */
  
  #ifndef __hidden
  #   if defined(__GNUC__) || __has_attribute(__visibility__)
  #       define __hidden __attribute__((__visibility__("hidden")))
  #   else
  #       define __hidden
  #   endif
  #endif /* __hidden */
  
  #ifndef __optimize
  #   if defined(__OPTIMIZE__)
  #       if (defined(__GNUC__) && !defined(__clang__)) || __has_attribute(__optimize__)
  #           define __optimize(ops) __attribute__((__optimize__(ops)))
  #       else
  #           define __optimize(ops)
  #       endif
  #   else
  #       define __optimize(ops)
  #   endif
  #endif /* __optimize */
  
  #ifndef __hot
  #   if defined(__OPTIMIZE__)
  #       if defined(__e2k__)
  #           define __hot __attribute__((__hot__)) __optimize(3)
  #       elif defined(__clang__) && !__has_attribute(__hot_) \
          && __has_attribute(__section__) && (defined(__linux__) || defined(__gnu_linux__))
              /* just put frequently used functions in separate section */
  #           define __hot __attribute__((__section__("text.hot"))) __optimize("O3")
  #       elif defined(__GNUC__) || __has_attribute(__hot__)
  #           define __hot __attribute__((__hot__)) __optimize("O3")
  #       else
  #           define __hot  __optimize("O3")
  #       endif
  #   else
  #       define __hot
  #   endif
  #endif /* __hot */
  
  #ifndef __cold
  #   if defined(__OPTIMIZE__)
  #       if defined(__e2k__)
  #           define __cold __attribute__((__cold__)) __optimize(1)
  #       elif defined(__clang__) && !__has_attribute(cold) \
          && __has_attribute(__section__) && (defined(__linux__) || defined(__gnu_linux__))
              /* just put infrequently used functions in separate section */
  #           define __cold __attribute__((__section__("text.unlikely"))) __optimize("Os")
  #       elif defined(__GNUC__) || __has_attribute(cold)
  #           define __cold __attribute__((__cold__)) __optimize("Os")
  #       else
  #           define __cold __optimize("Os")
  #       endif
  #   else
  #       define __cold
  #   endif
  #endif /* __cold */
  
  #ifndef __flatten
  #   if defined(__OPTIMIZE__) && (defined(__GNUC__) || __has_attribute(__flatten__))
  #       define __flatten __attribute__((__flatten__))
  #   else
  #       define __flatten
  #   endif
  #endif /* __flatten */
  
  #ifndef likely
  #   if (defined(__GNUC__) || __has_builtin(__builtin_expect)) && !defined(__COVERITY__)
  #       define likely(cond) __builtin_expect(!!(cond), 1)
  #   else
  #       define likely(x) (x)
  #   endif
  #endif /* likely */
  
  #ifndef unlikely
  #   if (defined(__GNUC__) || __has_builtin(__builtin_expect)) && !defined(__COVERITY__)
  #       define unlikely(cond) __builtin_expect(!!(cond), 0)
  #   else
  #       define unlikely(x) (x)
  #   endif
  #endif /* unlikely */
  
  #ifndef __anonymous_struct_extension__
  #   if defined(__GNUC__)
  #       define __anonymous_struct_extension__ __extension__
  #   else
  #       define __anonymous_struct_extension__
  #   endif
  #endif /* __anonymous_struct_extension__ */
  
  #ifndef __Wpedantic_format_voidptr
      static __inline __maybe_unused const void* MDBX_PURE_FUNCTION
          __Wpedantic_format_voidptr(const void* ptr) {return ptr;}
  #   define __Wpedantic_format_voidptr(ARG) __Wpedantic_format_voidptr(ARG)
  #endif /* __Wpedantic_format_voidptr */
  
  /*----------------------------------------------------------------------------*/
  
  #if defined(MDBX_USE_VALGRIND)
  #   include <valgrind/memcheck.h>
  #   ifndef VALGRIND_DISABLE_ADDR_ERROR_REPORTING_IN_RANGE
          /* LY: available since Valgrind 3.10 */
  #       define VALGRIND_DISABLE_ADDR_ERROR_REPORTING_IN_RANGE(a,s)
  #       define VALGRIND_ENABLE_ADDR_ERROR_REPORTING_IN_RANGE(a,s)
  #   endif
  #elif !defined(RUNNING_ON_VALGRIND)
  #   define VALGRIND_CREATE_MEMPOOL(h,r,z)
  #   define VALGRIND_DESTROY_MEMPOOL(h)
  #   define VALGRIND_MEMPOOL_TRIM(h,a,s)
  #   define VALGRIND_MEMPOOL_ALLOC(h,a,s)
  #   define VALGRIND_MEMPOOL_FREE(h,a)
  #   define VALGRIND_MEMPOOL_CHANGE(h,a,b,s)
  #   define VALGRIND_MAKE_MEM_NOACCESS(a,s)
  #   define VALGRIND_MAKE_MEM_DEFINED(a,s)
  #   define VALGRIND_MAKE_MEM_UNDEFINED(a,s)
  #   define VALGRIND_DISABLE_ADDR_ERROR_REPORTING_IN_RANGE(a,s)
  #   define VALGRIND_ENABLE_ADDR_ERROR_REPORTING_IN_RANGE(a,s)
  #   define VALGRIND_CHECK_MEM_IS_ADDRESSABLE(a,s) (0)
  #   define VALGRIND_CHECK_MEM_IS_DEFINED(a,s) (0)
  #   define RUNNING_ON_VALGRIND (0)
  #endif /* MDBX_USE_VALGRIND */
  
  #ifdef __SANITIZE_ADDRESS__
  #   include <sanitizer/asan_interface.h>
  #elif !defined(ASAN_POISON_MEMORY_REGION)
  #   define ASAN_POISON_MEMORY_REGION(addr, size) \
          ((void)(addr), (void)(size))
  #   define ASAN_UNPOISON_MEMORY_REGION(addr, size) \
          ((void)(addr), (void)(size))
  #endif /* __SANITIZE_ADDRESS__ */
  
  /*----------------------------------------------------------------------------*/
  
  #ifndef ARRAY_LENGTH
  #   ifdef __cplusplus
          template <typename T, size_t N>
          char (&__ArraySizeHelper(T (&array)[N]))[N];
  #       define ARRAY_LENGTH(array) (sizeof(::__ArraySizeHelper(array)))
  #   else
  #       define ARRAY_LENGTH(array) (sizeof(array) / sizeof(array[0]))
  #   endif
  #endif /* ARRAY_LENGTH */
  
  #ifndef ARRAY_END
  #   define ARRAY_END(array) (&array[ARRAY_LENGTH(array)])
  #endif /* ARRAY_END */
  
  #ifndef STRINGIFY
  #   define STRINGIFY_HELPER(x) #x
  #   define STRINGIFY(x) STRINGIFY_HELPER(x)
  #endif /* STRINGIFY */
  
  #define CONCAT(a,b) a##b
  #define XCONCAT(a,b) CONCAT(a,b)
  
  #ifndef offsetof
  #   define offsetof(type, member)  __builtin_offsetof(type, member)
  #endif /* offsetof */
  
  #ifndef container_of
  #   define container_of(ptr, type, member) \
          ((type *)((char *)(ptr) - offsetof(type, member)))
  #endif /* container_of */
  
  #define MDBX_TETRAD(a, b, c, d)                                                \
    ((uint32_t)(a) << 24 | (uint32_t)(b) << 16 | (uint32_t)(c) << 8 | (d))
  
  #define MDBX_STRING_TETRAD(str) MDBX_TETRAD(str[0], str[1], str[2], str[3])
  
  #define FIXME "FIXME: " __FILE__ ", " STRINGIFY(__LINE__)
  
  #ifndef STATIC_ASSERT_MSG
  #   if defined(static_assert)
  #       define STATIC_ASSERT_MSG(expr, msg) static_assert(expr, msg)
  #   elif defined(_STATIC_ASSERT)
  #       define STATIC_ASSERT_MSG(expr, msg) _STATIC_ASSERT(expr)
  #   elif defined(_MSC_VER)
  #       include <crtdbg.h>
  #       define STATIC_ASSERT_MSG(expr, msg) _STATIC_ASSERT(expr)
  #   elif (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) \
            || __has_feature(c_static_assert)
  #       define STATIC_ASSERT_MSG(expr, msg) _Static_assert(expr, msg)
  #   else
  #       define STATIC_ASSERT_MSG(expr, msg) switch (0) {case 0:case (expr):;}
  #   endif
  #endif /* STATIC_ASSERT */
  
  #ifndef STATIC_ASSERT
  #   define STATIC_ASSERT(expr) STATIC_ASSERT_MSG(expr, #expr)
  #endif
  
  /* *INDENT-ON* */
  /* clang-format on */
  
  #if defined(__GNUC__) && !__GNUC_PREREQ(4,2)
      /* Actually libmdbx was not tested with compilers older than GCC 4.2.
       * But you could ignore this warning at your own risk.
       * In such case please don't rise up an issues related ONLY to old compilers.
       */
  #   warning "libmdbx required GCC >= 4.2"
  #endif
  
  #if defined(__clang__) && !__CLANG_PREREQ(3,8)
      /* Actually libmdbx was not tested with CLANG older than 3.8.
       * But you could ignore this warning at your own risk.
       * In such case please don't rise up an issues related ONLY to old compilers.
       */
  #   warning "libmdbx required CLANG >= 3.8"
  #endif
  
  #if defined(__GLIBC__) && !__GLIBC_PREREQ(2,12)
      /* Actually libmdbx was not tested with something older than glibc 2.12.
       * But you could ignore this warning at your own risk.
       * In such case please don't rise up an issues related ONLY to old systems.
       */
  #   warning "libmdbx was only tested with GLIBC >= 2.12."
  #endif
  
  #ifdef __SANITIZE_THREAD__
  #   warning "libmdbx don't compatible with ThreadSanitizer, you will get a lot of false-positive issues."
  #endif /* __SANITIZE_THREAD__ */
  
  #if __has_warning("-Wnested-anon-types")
  #   if defined(__clang__)
  #       pragma clang diagnostic ignored "-Wnested-anon-types"
  #   elif defined(__GNUC__)
  #       pragma GCC diagnostic ignored "-Wnested-anon-types"
  #   else
  #      pragma warning disable "nested-anon-types"
  #   endif
  #endif /* -Wnested-anon-types */
  
  #if __has_warning("-Wconstant-logical-operand")
  #   if defined(__clang__)
  #       pragma clang diagnostic ignored "-Wconstant-logical-operand"
  #   elif defined(__GNUC__)
  #       pragma GCC diagnostic ignored "-Wconstant-logical-operand"
  #   else
  #      pragma warning disable "constant-logical-operand"
  #   endif
  #endif /* -Wconstant-logical-operand */
  
  #if defined(__LCC__) && (__LCC__ <= 121)
      /* bug #2798 */
  #   pragma diag_suppress alignment_reduction_ignored
  #elif defined(__ICC)
  #   pragma warning(disable: 3453 1366)
  #elif __has_warning("-Walignment-reduction-ignored")
  #   if defined(__clang__)
  #       pragma clang diagnostic ignored "-Walignment-reduction-ignored"
  #   elif defined(__GNUC__)
  #       pragma GCC diagnostic ignored "-Walignment-reduction-ignored"
  #   else
  #       pragma warning disable "alignment-reduction-ignored"
  #   endif
  #endif /* -Walignment-reduction-ignored */
  
  /* *INDENT-ON* */
  /* clang-format on */
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /* https://en.wikipedia.org/wiki/Operating_system_abstraction_layer */
  
  /*
   * Copyright 2015-2020 Leonid Yuriev <leo@yuriev.ru>
   * and other libmdbx authors: please see AUTHORS file.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted only as authorized by the OpenLDAP
   * Public License.
   *
   * A copy of this license is available in the file LICENSE in the
   * top-level directory of the distribution or, alternatively, at
   * <http://www.OpenLDAP.org/license.html>.
   */
  
  
  /*----------------------------------------------------------------------------*/
  /* Microsoft compiler generates a lot of warning for self includes... */
  
  #ifdef _MSC_VER
  #pragma warning(push, 1)
  #pragma warning(disable : 4548) /* expression before comma has no effect;      \
                                     expected expression with side - effect */
  #pragma warning(disable : 4530) /* C++ exception handler used, but unwind      \
                                   * semantics are not enabled. Specify /EHsc */
  #pragma warning(disable : 4577) /* 'noexcept' used with no exception handling  \
                                   * mode specified; termination on exception is \
                                   * not guaranteed. Specify /EHsc */
  #endif                          /* _MSC_VER (warnings) */
  
  #if defined(_WIN32) || defined(_WIN64)
  #if !defined(_CRT_SECURE_NO_WARNINGS)
  #define _CRT_SECURE_NO_WARNINGS
  #endif
  #if !defined(_NO_CRT_STDIO_INLINE) && MDBX_BUILD_SHARED_LIBRARY &&             \
      !defined(MDBX_TOOLS) && MDBX_AVOID_CRT
  #define _NO_CRT_STDIO_INLINE
  #endif
  #elif !defined(_POSIX_C_SOURCE)
  #define _POSIX_C_SOURCE 200809L
  #endif /* Windows */
  
  /*----------------------------------------------------------------------------*/
  /* C99 includes */
  #include <inttypes.h>
  #include <stddef.h>
  #include <stdint.h>
  #include <stdlib.h>
  
  #include <assert.h>
  #include <fcntl.h>
  #include <limits.h>
  #include <stdio.h>
  #include <string.h>
  #include <time.h>
  
  /* C11 stdalign.h */
  #if __has_include(<stdalign.h>)
  #include <stdalign.h>
  #elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
  #define alignas(N) _Alignas(N)
  #elif defined(_MSC_VER)
  #define alignas(N) __declspec(align(N))
  #elif __has_attribute(__aligned__) || defined(__GNUC__)
  #define alignas(N) __attribute__((__aligned__(N)))
  #else
  #error "FIXME: Required _alignas() or equivalent."
  #endif
  
  /*----------------------------------------------------------------------------*/
  /* Systems includes */
  
  #ifdef __APPLE__
  #include <TargetConditionals.h>
  #endif /* Apple OSX & iOS */
  
  #if defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) ||     \
      defined(__BSD__) || defined(__bsdi__) || defined(__DragonFly__) ||         \
      defined(__APPLE__) || defined(__MACH__)
  #include <sys/cdefs.h>
  #include <sys/mount.h>
  #include <sys/sysctl.h>
  #include <sys/types.h>
  #if defined(__FreeBSD__) || defined(__DragonFly__)
  #include <vm/vm_param.h>
  #elif defined(__OpenBSD__) || defined(__NetBSD__)
  #include <uvm/uvm_param.h>
  #else
  #define SYSCTL_LEGACY_NONCONST_MIB
  #endif
  #ifndef __MACH__
  #include <sys/vmmeter.h>
  #endif
  #else
  #include <malloc.h>
  #if !(defined(__sun) || defined(__SVR4) || defined(__svr4__) ||                \
        defined(_WIN32) || defined(_WIN64))
  #include <mntent.h>
  #endif /* !Solaris */
  #endif /* !xBSD */
  
  #if defined(__FreeBSD__) || __has_include(<malloc_np.h>)
  #include <malloc_np.h>
  #endif
  
  #if defined(__APPLE__) || defined(__MACH__) || __has_include(<malloc/malloc.h>)
  #include <malloc/malloc.h>
  #endif /* MacOS */
  
  #if defined(__MACH__)
  #include <mach/host_info.h>
  #include <mach/mach_host.h>
  #include <mach/mach_port.h>
  #include <uuid/uuid.h>
  #undef P_DIRTY
  #endif
  
  #if defined(__linux__) || defined(__gnu_linux__)
  #include <linux/sysctl.h>
  #include <sched.h>
  #include <sys/sendfile.h>
  #include <sys/statfs.h>
  #endif /* Linux */
  
  #ifndef _XOPEN_SOURCE
  #define _XOPEN_SOURCE 0
  #endif
  
  #ifndef _XOPEN_SOURCE_EXTENDED
  #define _XOPEN_SOURCE_EXTENDED 0
  #else
  #include <utmpx.h>
  #endif /* _XOPEN_SOURCE_EXTENDED */
  
  #if defined(__sun) || defined(__SVR4) || defined(__svr4__)
  #include <kstat.h>
  #include <sys/mnttab.h>
  /* On Solaris, it's easier to add a missing prototype rather than find a
   * combination of #defines that break nothing. */
  __extern_C key_t ftok(const char *, int);
  #endif /* SunOS/Solaris */
  
  #if defined(_WIN32) || defined(_WIN64)
  #ifndef WIN32_LEAN_AND_MEAN
  #define WIN32_LEAN_AND_MEAN
  #endif
  #include <excpt.h>
  #include <tlhelp32.h>
  #include <windows.h>
  #include <winnt.h>
  #include <winternl.h>
  #define HAVE_SYS_STAT_H
  #define HAVE_SYS_TYPES_H
  typedef HANDLE mdbx_thread_t;
  typedef unsigned mdbx_thread_key_t;
  #define MDBX_OSAL_SECTION HANDLE
  #define MAP_FAILED NULL
  #define HIGH_DWORD(v) ((DWORD)((sizeof(v) > 4) ? ((uint64_t)(v) >> 32) : 0))
  #define THREAD_CALL WINAPI
  #define THREAD_RESULT DWORD
  typedef struct {
    HANDLE mutex;
    HANDLE event[2];
  } mdbx_condpair_t;
  typedef CRITICAL_SECTION mdbx_fastmutex_t;
  
  #if MDBX_AVOID_CRT
  #ifndef mdbx_malloc
  static inline void *mdbx_malloc(size_t bytes) {
    return LocalAlloc(LMEM_FIXED, bytes);
  }
  #endif /* mdbx_malloc */
  
  #ifndef mdbx_calloc
  static inline void *mdbx_calloc(size_t nelem, size_t size) {
    return LocalAlloc(LMEM_FIXED | LMEM_ZEROINIT, nelem * size);
  }
  #endif /* mdbx_calloc */
  
  #ifndef mdbx_realloc
  static inline void *mdbx_realloc(void *ptr, size_t bytes) {
    return ptr ? LocalReAlloc(ptr, bytes, LMEM_MOVEABLE)
               : LocalAlloc(LMEM_FIXED, bytes);
  }
  #endif /* mdbx_realloc */
  
  #ifndef mdbx_free
  #define mdbx_free LocalFree
  #endif /* mdbx_free */
  #else
  #define mdbx_malloc malloc
  #define mdbx_calloc calloc
  #define mdbx_realloc realloc
  #define mdbx_free free
  #define mdbx_strdup _strdup
  #endif /* MDBX_AVOID_CRT */
  
  #ifndef snprintf
  #define snprintf _snprintf /* ntdll */
  #endif
  
  #ifndef vsnprintf
  #define vsnprintf _vsnprintf /* ntdll */
  #endif
  
  #else /*----------------------------------------------------------------------*/
  
  #include <pthread.h>
  #include <semaphore.h>
  #include <signal.h>
  #include <sys/file.h>
  #include <sys/ipc.h>
  #include <sys/mman.h>
  #include <sys/param.h>
  #include <sys/stat.h>
  #include <sys/statvfs.h>
  #include <sys/uio.h>
  #include <unistd.h>
  typedef pthread_t mdbx_thread_t;
  typedef pthread_key_t mdbx_thread_key_t;
  #define INVALID_HANDLE_VALUE (-1)
  #define THREAD_CALL
  #define THREAD_RESULT void *
  typedef struct {
    pthread_mutex_t mutex;
    pthread_cond_t cond[2];
  } mdbx_condpair_t;
  typedef pthread_mutex_t mdbx_fastmutex_t;
  #define mdbx_malloc malloc
  #define mdbx_calloc calloc
  #define mdbx_realloc realloc
  #define mdbx_free free
  #define mdbx_strdup strdup
  #endif /* Platform */
  
  #if __GLIBC_PREREQ(2, 12) || defined(__FreeBSD__) || defined(malloc_usable_size)
  /* malloc_usable_size() already provided */
  #elif defined(__APPLE__)
  #define malloc_usable_size(ptr) malloc_size(ptr)
  #elif defined(_MSC_VER) && !MDBX_AVOID_CRT
  #define malloc_usable_size(ptr) _msize(ptr)
  #endif /* malloc_usable_size */
  
  #ifdef __ANDROID_API__
  #include <android/log.h>
  #if __ANDROID_API__ >= 21
  #include <sys/sendfile.h>
  #endif
  #endif /* Android */
  
  /* *INDENT-OFF* */
  /* clang-format off */
  #if defined(HAVE_SYS_STAT_H) || __has_include(<sys/stat.h>)
  #include <sys/stat.h>
  #endif
  #if defined(HAVE_SYS_TYPES_H) || __has_include(<sys/types.h>)
  #include <sys/types.h>
  #endif
  #if defined(HAVE_SYS_FILE_H) || __has_include(<sys/file.h>)
  #include <sys/file.h>
  #endif
  /* *INDENT-ON* */
  /* clang-format on */
  
  #ifndef SSIZE_MAX
  #define SSIZE_MAX INTPTR_MAX
  #endif
  
  #if !defined(MADV_DODUMP) && defined(MADV_CORE)
  #define MADV_DODUMP MADV_CORE
  #endif /* MADV_CORE -> MADV_DODUMP */
  
  #if !defined(MADV_DONTDUMP) && defined(MADV_NOCORE)
  #define MADV_DONTDUMP MADV_NOCORE
  #endif /* MADV_NOCORE -> MADV_DONTDUMP */
  
  #if defined(i386) || defined(__386) || defined(__i386) || defined(__i386__) || \
      defined(i486) || defined(__i486) || defined(__i486__) ||                   \
      defined(i586) | defined(__i586) || defined(__i586__) || defined(i686) ||   \
      defined(__i686) || defined(__i686__) || defined(_M_IX86) ||                \
      defined(_X86_) || defined(__THW_INTEL__) || defined(__I86__) ||            \
      defined(__INTEL__) || defined(__x86_64) || defined(__x86_64__) ||          \
      defined(__amd64__) || defined(__amd64) || defined(_M_X64) ||               \
      defined(_M_AMD64) || defined(__IA32__) || defined(__INTEL__)
  #ifndef __ia32__
  /* LY: define neutral __ia32__ for x86 and x86-64 */
  #define __ia32__ 1
  #endif /* __ia32__ */
  #if !defined(__amd64__) && (defined(__x86_64) || defined(__x86_64__) ||        \
                              defined(__amd64) || defined(_M_X64))
  /* LY: define trusty __amd64__ for all AMD64/x86-64 arch */
  #define __amd64__ 1
  #endif /* __amd64__ */
  #endif /* all x86 */
  
  #if (-6 & 5) || CHAR_BIT != 8 || UINT_MAX < 0xffffffff || ULONG_MAX % 0xFFFF
  #error                                                                         \
      "Sanity checking failed: Two's complement, reasonably sized integer types"
  #endif
  
  #if UINTPTR_MAX > 0xffffFFFFul || ULONG_MAX > 0xffffFFFFul
  #define MDBX_WORDBITS 64
  #else
  #define MDBX_WORDBITS 32
  #endif /* MDBX_WORDBITS */
  
  /*----------------------------------------------------------------------------*/
  /* Compiler's includes for builtins/intrinsics */
  
  #if defined(_MSC_VER) || defined(__INTEL_COMPILER)
  #include <intrin.h>
  #elif __GNUC_PREREQ(4, 4) || defined(__clang__)
  #if defined(__ia32__) || defined(__e2k__)
  #include <x86intrin.h>
  #endif /* __ia32__ */
  #if defined(__ia32__)
  #include <cpuid.h>
  #endif /* __ia32__ */
  #elif defined(__SUNPRO_C) || defined(__sun) || defined(sun)
  #include <mbarrier.h>
  #elif (defined(_HPUX_SOURCE) || defined(__hpux) || defined(__HP_aCC)) &&       \
      (defined(HP_IA64) || defined(__ia64))
  #include <machine/sys/inline.h>
  #elif defined(__IBMC__) && defined(__powerpc)
  #include <atomic.h>
  #elif defined(_AIX)
  #include <builtins.h>
  #include <sys/atomic_op.h>
  #elif (defined(__osf__) && defined(__DECC)) || defined(__alpha)
  #include <c_asm.h>
  #include <machine/builtins.h>
  #elif defined(__MWERKS__)
  /* CodeWarrior - troubles ? */
  #pragma gcc_extensions
  #elif defined(__SNC__)
  /* Sony PS3 - troubles ? */
  #elif defined(__hppa__) || defined(__hppa)
  #include <machine/inline.h>
  #else
  #error Unsupported C compiler, please use GNU C 4.4 or newer
  #endif /* Compiler */
  
  /*----------------------------------------------------------------------------*/
  /* Byteorder */
  
  #if !defined(__BYTE_ORDER__) || !defined(__ORDER_LITTLE_ENDIAN__) ||           \
      !defined(__ORDER_BIG_ENDIAN__)
  
  /* *INDENT-OFF* */
  /* clang-format off */
  #if defined(__GLIBC__) || defined(__GNU_LIBRARY__) || defined(__ANDROID_API__) ||  \
      defined(HAVE_ENDIAN_H) || __has_include(<endian.h>)
  #include <endian.h>
  #elif defined(__APPLE__) || defined(__MACH__) || defined(__OpenBSD__) ||       \
      defined(HAVE_MACHINE_ENDIAN_H) || __has_include(<machine/endian.h>)
  #include <machine/endian.h>
  #elif defined(HAVE_SYS_ISA_DEFS_H) || __has_include(<sys/isa_defs.h>)
  #include <sys/isa_defs.h>
  #elif (defined(HAVE_SYS_TYPES_H) && defined(HAVE_SYS_ENDIAN_H)) ||             \
      (__has_include(<sys/types.h>) && __has_include(<sys/endian.h>))
  #include <sys/endian.h>
  #include <sys/types.h>
  #elif defined(__bsdi__) || defined(__DragonFly__) || defined(__FreeBSD__) ||   \
      defined(__NetBSD__) ||                              \
      defined(HAVE_SYS_PARAM_H) || __has_include(<sys/param.h>)
  #include <sys/param.h>
  #endif /* OS */
  /* *INDENT-ON* */
  /* clang-format on */
  
  #if defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && defined(__BIG_ENDIAN)
  #define __ORDER_LITTLE_ENDIAN__ __LITTLE_ENDIAN
  #define __ORDER_BIG_ENDIAN__ __BIG_ENDIAN
  #define __BYTE_ORDER__ __BYTE_ORDER
  #elif defined(_BYTE_ORDER) && defined(_LITTLE_ENDIAN) && defined(_BIG_ENDIAN)
  #define __ORDER_LITTLE_ENDIAN__ _LITTLE_ENDIAN
  #define __ORDER_BIG_ENDIAN__ _BIG_ENDIAN
  #define __BYTE_ORDER__ _BYTE_ORDER
  #else
  #define __ORDER_LITTLE_ENDIAN__ 1234
  #define __ORDER_BIG_ENDIAN__ 4321
  
  #if defined(__LITTLE_ENDIAN__) ||                                              \
      (defined(_LITTLE_ENDIAN) && !defined(_BIG_ENDIAN)) ||                      \
      defined(__ARMEL__) || defined(__THUMBEL__) || defined(__AARCH64EL__) ||    \
      defined(__MIPSEL__) || defined(_MIPSEL) || defined(__MIPSEL) ||            \
      defined(_M_ARM) || defined(_M_ARM64) || defined(__e2k__) ||                \
      defined(__elbrus_4c__) || defined(__elbrus_8c__) || defined(__bfin__) ||   \
      defined(__BFIN__) || defined(__ia64__) || defined(_IA64) ||                \
      defined(__IA64__) || defined(__ia64) || defined(_M_IA64) ||                \
      defined(__itanium__) || defined(__ia32__) || defined(__CYGWIN__) ||        \
      defined(_WIN64) || defined(_WIN32) || defined(__TOS_WIN__) ||              \
      defined(__WINDOWS__)
  #define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
  
  #elif defined(__BIG_ENDIAN__) ||                                               \
      (defined(_BIG_ENDIAN) && !defined(_LITTLE_ENDIAN)) ||                      \
      defined(__ARMEB__) || defined(__THUMBEB__) || defined(__AARCH64EB__) ||    \
      defined(__MIPSEB__) || defined(_MIPSEB) || defined(__MIPSEB) ||            \
      defined(__m68k__) || defined(M68000) || defined(__hppa__) ||               \
      defined(__hppa) || defined(__HPPA__) || defined(__sparc__) ||              \
      defined(__sparc) || defined(__370__) || defined(__THW_370__) ||            \
      defined(__s390__) || defined(__s390x__) || defined(__SYSC_ZARCH__)
  #define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
  
  #else
  #error __BYTE_ORDER__ should be defined.
  #endif /* Arch */
  
  #endif
  #endif /* __BYTE_ORDER__ || __ORDER_LITTLE_ENDIAN__ || __ORDER_BIG_ENDIAN__ */
  
  /* Get the size of a memory page for the system.
   * This is the basic size that the platform's memory manager uses, and is
   * fundamental to the use of memory-mapped files. */
  MDBX_NOTHROW_CONST_FUNCTION static __maybe_unused __inline size_t
  mdbx_syspagesize(void) {
  #if defined(_WIN32) || defined(_WIN64)
    SYSTEM_INFO si;
    GetSystemInfo(&si);
    return si.dwPageSize;
  #else
    return sysconf(_SC_PAGE_SIZE);
  #endif
  }
  
  typedef struct mdbx_mmap_param {
    union {
      void *address;
      uint8_t *dxb;
      struct MDBX_lockinfo *lck;
    };
    mdbx_filehandle_t fd;
    size_t limit;   /* mapping length, but NOT a size of file nor DB */
    size_t current; /* mapped region size, i.e. the size of file and DB */
  #if defined(_WIN32) || defined(_WIN64)
    uint64_t filesize /* in-process cache of a file size. */;
  #endif
  #ifdef MDBX_OSAL_SECTION
    MDBX_OSAL_SECTION section;
  #endif
  } mdbx_mmap_t;
  
  typedef union bin128 {
    __anonymous_struct_extension__ struct { uint64_t x, y; };
    __anonymous_struct_extension__ struct { uint32_t a, b, c, d; };
  } bin128_t;
  
  #if defined(_WIN32) || defined(_WIN64)
  typedef union MDBX_srwlock {
    struct {
      long volatile readerCount;
      long volatile writerCount;
    };
    RTL_SRWLOCK native;
  } MDBX_srwlock;
  #endif /* Windows */
  
  #ifdef __cplusplus
  extern void mdbx_osal_jitter(bool tiny);
  #else
  
  /*----------------------------------------------------------------------------*/
  /* Atomics */
  
  #if defined(__cplusplus) && !defined(__STDC_NO_ATOMICS__) && __has_include(<cstdatomic>)
  #include <cstdatomic>
  #elif !defined(__cplusplus) && (__STDC_VERSION__ >= 201112L) &&                \
      !defined(__STDC_NO_ATOMICS__) &&                                           \
      (__GNUC_PREREQ(4, 9) || __CLANG_PREREQ(3, 8) ||                            \
       !(defined(__GNUC__) || defined(__clang__)))
  #include <stdatomic.h>
  #elif defined(__GNUC__) || defined(__clang__)
  /* LY: nothing required */
  #elif defined(_MSC_VER)
  #pragma warning(disable : 4163) /* 'xyz': not available as an intrinsic */
  #pragma warning(disable : 4133) /* 'function': incompatible types - from       \
                                     'size_t' to 'LONGLONG' */
  #pragma warning(disable : 4244) /* 'return': conversion from 'LONGLONG' to     \
                                     'std::size_t', possible loss of data */
  #pragma warning(disable : 4267) /* 'function': conversion from 'size_t' to     \
                                     'long', possible loss of data */
  #pragma intrinsic(_InterlockedExchangeAdd, _InterlockedCompareExchange)
  #pragma intrinsic(_InterlockedExchangeAdd64, _InterlockedCompareExchange64)
  #elif defined(__APPLE__)
  #include <libkern/OSAtomic.h>
  #else
  #error FIXME atomic-ops
  #endif
  
  /*----------------------------------------------------------------------------*/
  /* Memory/Compiler barriers, cache coherence */
  
  #if __has_include(<sys/cachectl.h>)
  #include <sys/cachectl.h>
  #elif defined(__mips) || defined(__mips__) || defined(__mips64) ||             \
      defined(__mips64__) || defined(_M_MRX000) || defined(_MIPS_) ||            \
      defined(__MWERKS__) || defined(__sgi)
  /* MIPS should have explicit cache control */
  #include <sys/cachectl.h>
  #endif
  
  static __maybe_unused __inline void mdbx_compiler_barrier(void) {
  #if defined(__clang__) || defined(__GNUC__)
    __asm__ __volatile__("" ::: "memory");
  #elif defined(_MSC_VER)
    _ReadWriteBarrier();
  #elif defined(__INTEL_COMPILER) /* LY: Intel Compiler may mimic GCC and MSC */
    __memory_barrier();
    if (type > MDBX_BARRIER_COMPILER)
  #if defined(__ia64__) || defined(__ia64) || defined(_M_IA64)
      __mf();
  #elif defined(__i386__) || defined(__x86_64__)
      _mm_mfence();
  #else
  #error "Unknown target for Intel Compiler, please report to us."
  #endif
  #elif defined(__SUNPRO_C) || defined(__sun) || defined(sun)
    __compiler_barrier();
  #elif (defined(_HPUX_SOURCE) || defined(__hpux) || defined(__HP_aCC)) &&       \
      (defined(HP_IA64) || defined(__ia64))
    _Asm_sched_fence(/* LY: no-arg meaning 'all expect ALU', e.g. 0x3D3D */);
  #elif defined(_AIX) || defined(__ppc__) || defined(__powerpc__) ||             \
      defined(__ppc64__) || defined(__powerpc64__)
    __fence();
  #else
  #error "Could not guess the kind of compiler, please report to us."
  #endif
  }
  
  static __maybe_unused __inline void mdbx_memory_barrier(void) {
  #if __has_extension(c_atomic) && !defined(__STDC_NO_ATOMICS__)
    atomic_thread_fence(__ATOMIC_SEQ_CST);
  #elif defined(__ATOMIC_SEQ_CST)
    __atomic_thread_fence(__ATOMIC_SEQ_CST);
  #elif defined(__clang__) || defined(__GNUC__)
    __sync_synchronize();
  #elif defined(_MSC_VER)
    MemoryBarrier();
  #elif defined(__INTEL_COMPILER) /* LY: Intel Compiler may mimic GCC and MSC */
  #if defined(__ia64__) || defined(__ia64) || defined(_M_IA64)
    __mf();
  #elif defined(__i386__) || defined(__x86_64__)
    _mm_mfence();
  #else
  #error "Unknown target for Intel Compiler, please report to us."
  #endif
  #elif defined(__SUNPRO_C) || defined(__sun) || defined(sun)
    __machine_rw_barrier();
  #elif (defined(_HPUX_SOURCE) || defined(__hpux) || defined(__HP_aCC)) &&       \
      (defined(HP_IA64) || defined(__ia64))
    _Asm_mf();
  #elif defined(_AIX) || defined(__ppc__) || defined(__powerpc__) ||             \
      defined(__ppc64__) || defined(__powerpc64__)
    __lwsync();
  #else
  #error "Could not guess the kind of compiler, please report to us."
  #endif
  }
  
  /*----------------------------------------------------------------------------*/
  /* libc compatibility stuff */
  
  #if (!defined(__GLIBC__) && __GLIBC_PREREQ(2, 1)) &&                           \
      (defined(_GNU_SOURCE) || defined(_BSD_SOURCE))
  #define mdbx_asprintf asprintf
  #define mdbx_vasprintf vasprintf
  #else
  MDBX_INTERNAL_FUNC MDBX_PRINTF_ARGS(2, 3) int __maybe_unused
      mdbx_asprintf(char **strp, const char *fmt, ...);
  MDBX_INTERNAL_FUNC int mdbx_vasprintf(char **strp, const char *fmt, va_list ap);
  #endif
  
  /*----------------------------------------------------------------------------*/
  /* OS abstraction layer stuff */
  
  /* max bytes to write in one call */
  #if defined(_WIN32) || defined(_WIN64)
  #define MAX_WRITE UINT32_C(0x01000000)
  #else
  #define MAX_WRITE UINT32_C(0x3fff0000)
  #endif
  
  #if defined(__linux__) || defined(__gnu_linux__)
  MDBX_INTERNAL_VAR uint32_t mdbx_linux_kernel_version;
  MDBX_INTERNAL_VAR bool mdbx_RunningOnWSL1 /* Windows Subsystem 1 for Linux */;
  #endif /* Linux */
  
  #ifndef mdbx_strdup
  LIBMDBX_API char *mdbx_strdup(const char *str);
  #endif
  
  static __maybe_unused __inline int mdbx_get_errno(void) {
  #if defined(_WIN32) || defined(_WIN64)
    DWORD rc = GetLastError();
  #else
    int rc = errno;
  #endif
    return rc;
  }
  
  #ifndef mdbx_memalign_alloc
  MDBX_INTERNAL_FUNC int mdbx_memalign_alloc(size_t alignment, size_t bytes,
                                             void **result);
  #endif
  #ifndef mdbx_memalign_free
  MDBX_INTERNAL_FUNC void mdbx_memalign_free(void *ptr);
  #endif
  
  MDBX_INTERNAL_FUNC int mdbx_condpair_init(mdbx_condpair_t *condpair);
  MDBX_INTERNAL_FUNC int mdbx_condpair_lock(mdbx_condpair_t *condpair);
  MDBX_INTERNAL_FUNC int mdbx_condpair_unlock(mdbx_condpair_t *condpair);
  MDBX_INTERNAL_FUNC int mdbx_condpair_signal(mdbx_condpair_t *condpair,
                                              bool part);
  MDBX_INTERNAL_FUNC int mdbx_condpair_wait(mdbx_condpair_t *condpair, bool part);
  MDBX_INTERNAL_FUNC int mdbx_condpair_destroy(mdbx_condpair_t *condpair);
  
  MDBX_INTERNAL_FUNC int mdbx_fastmutex_init(mdbx_fastmutex_t *fastmutex);
  MDBX_INTERNAL_FUNC int mdbx_fastmutex_acquire(mdbx_fastmutex_t *fastmutex);
  MDBX_INTERNAL_FUNC int mdbx_fastmutex_release(mdbx_fastmutex_t *fastmutex);
  MDBX_INTERNAL_FUNC int mdbx_fastmutex_destroy(mdbx_fastmutex_t *fastmutex);
  
  MDBX_INTERNAL_FUNC int mdbx_pwritev(mdbx_filehandle_t fd, struct iovec *iov,
                                      int iovcnt, uint64_t offset,
                                      size_t expected_written);
  MDBX_INTERNAL_FUNC int mdbx_pread(mdbx_filehandle_t fd, void *buf, size_t count,
                                    uint64_t offset);
  MDBX_INTERNAL_FUNC int mdbx_pwrite(mdbx_filehandle_t fd, const void *buf,
                                     size_t count, uint64_t offset);
  MDBX_INTERNAL_FUNC int mdbx_write(mdbx_filehandle_t fd, const void *buf,
                                    size_t count);
  
  MDBX_INTERNAL_FUNC int
  mdbx_thread_create(mdbx_thread_t *thread,
                     THREAD_RESULT(THREAD_CALL *start_routine)(void *),
                     void *arg);
  MDBX_INTERNAL_FUNC int mdbx_thread_join(mdbx_thread_t thread);
  
  enum mdbx_syncmode_bits {
    MDBX_SYNC_NONE = 0,
    MDBX_SYNC_DATA = 1,
    MDBX_SYNC_SIZE = 2,
    MDBX_SYNC_IODQ = 4
  };
  
  MDBX_INTERNAL_FUNC int mdbx_fsync(mdbx_filehandle_t fd,
                                    const enum mdbx_syncmode_bits mode_bits);
  MDBX_INTERNAL_FUNC int mdbx_ftruncate(mdbx_filehandle_t fd, uint64_t length);
  MDBX_INTERNAL_FUNC int mdbx_fseek(mdbx_filehandle_t fd, uint64_t pos);
  MDBX_INTERNAL_FUNC int mdbx_filesize(mdbx_filehandle_t fd, uint64_t *length);
  
  enum mdbx_openfile_purpose {
    MDBX_OPEN_DXB_READ = 0,
    MDBX_OPEN_DXB_LAZY = 1,
    MDBX_OPEN_DXB_DSYNC = 2,
    MDBX_OPEN_LCK = 3,
    MDBX_OPEN_COPY = 4,
    MDBX_OPEN_DELETE = 5
  };
  
  MDBX_INTERNAL_FUNC int mdbx_openfile(const enum mdbx_openfile_purpose purpose,
                                       const MDBX_env *env, const char *pathname,
                                       mdbx_filehandle_t *fd,
                                       mdbx_mode_t unix_mode_bits);
  MDBX_INTERNAL_FUNC int mdbx_closefile(mdbx_filehandle_t fd);
  MDBX_INTERNAL_FUNC int mdbx_removefile(const char *pathname);
  MDBX_INTERNAL_FUNC int mdbx_removedirectory(const char *pathname);
  MDBX_INTERNAL_FUNC int mdbx_is_pipe(mdbx_filehandle_t fd);
  MDBX_INTERNAL_FUNC int mdbx_lockfile(mdbx_filehandle_t fd, bool wait);
  
  #define MMAP_OPTION_TRUNCATE 1
  #define MMAP_OPTION_SEMAPHORE 2
  MDBX_INTERNAL_FUNC int mdbx_mmap(const int flags, mdbx_mmap_t *map,
                                   const size_t must, const size_t limit,
                                   const unsigned options);
  MDBX_INTERNAL_FUNC int mdbx_munmap(mdbx_mmap_t *map);
  MDBX_INTERNAL_FUNC int mdbx_mresize(int flags, mdbx_mmap_t *map, size_t current,
                                      size_t wanna, const bool may_move);
  #if defined(_WIN32) || defined(_WIN64)
  typedef struct {
    unsigned limit, count;
    HANDLE handles[31];
  } mdbx_handle_array_t;
  MDBX_INTERNAL_FUNC int
  mdbx_suspend_threads_before_remap(MDBX_env *env, mdbx_handle_array_t **array);
  MDBX_INTERNAL_FUNC int
  mdbx_resume_threads_after_remap(mdbx_handle_array_t *array);
  #endif /* Windows */
  MDBX_INTERNAL_FUNC int mdbx_msync(mdbx_mmap_t *map, size_t offset,
                                    size_t length,
                                    enum mdbx_syncmode_bits mode_bits);
  MDBX_INTERNAL_FUNC int mdbx_check_fs_rdonly(mdbx_filehandle_t handle,
                                              const char *pathname, int err);
  
  static __maybe_unused __inline uint32_t mdbx_getpid(void) {
    STATIC_ASSERT(sizeof(mdbx_pid_t) <= sizeof(uint32_t));
  #if defined(_WIN32) || defined(_WIN64)
    return GetCurrentProcessId();
  #else
    return getpid();
  #endif
  }
  
  static __maybe_unused __inline uintptr_t mdbx_thread_self(void) {
    mdbx_tid_t thunk;
    STATIC_ASSERT(sizeof(uintptr_t) >= sizeof(thunk));
  #if defined(_WIN32) || defined(_WIN64)
    thunk = GetCurrentThreadId();
  #else
    thunk = pthread_self();
  #endif
    return (uintptr_t)thunk;
  }
  
  MDBX_INTERNAL_FUNC void __maybe_unused mdbx_osal_jitter(bool tiny);
  MDBX_INTERNAL_FUNC uint64_t mdbx_osal_monotime(void);
  MDBX_INTERNAL_FUNC uint64_t
  mdbx_osal_16dot16_to_monotime(uint32_t seconds_16dot16);
  MDBX_INTERNAL_FUNC uint32_t mdbx_osal_monotime_to_16dot16(uint64_t monotime);
  
  MDBX_INTERNAL_FUNC bin128_t mdbx_osal_bootid(void);
  /*----------------------------------------------------------------------------*/
  /* lck stuff */
  
  /// \brief Initialization of synchronization primitives linked with MDBX_env
  ///   instance both in LCK-file and within the current process.
  /// \param
  ///   global_uniqueness_flag = true - denotes that there are no other processes
  ///     working with DB and LCK-file. Thus the function MUST initialize
  ///     shared synchronization objects in memory-mapped LCK-file.
  ///   global_uniqueness_flag = false - denotes that at least one process is
  ///     already working with DB and LCK-file, including the case when DB
  ///     has already been opened in the current process. Thus the function
  ///     MUST NOT initialize shared synchronization objects in memory-mapped
  ///     LCK-file that are already in use.
  /// \return Error code or zero on success.
  MDBX_INTERNAL_FUNC int mdbx_lck_init(MDBX_env *env,
                                       MDBX_env *inprocess_neighbor,
                                       int global_uniqueness_flag);
  
  /// \brief Disconnects from shared interprocess objects and destructs
  ///   synchronization objects linked with MDBX_env instance
  ///   within the current process.
  /// \param
  ///   inprocess_neighbor = NULL - if the current process does not have other
  ///     instances of MDBX_env linked with the DB being closed.
  ///     Thus the function MUST check for other processes working with DB or
  ///     LCK-file, and keep or destroy shared synchronization objects in
  ///     memory-mapped LCK-file depending on the result.
  ///   inprocess_neighbor = not-NULL - pointer to another instance of MDBX_env
  ///     (anyone of there is several) working with DB or LCK-file within the
  ///     current process. Thus the function MUST NOT try to acquire exclusive
  ///     lock and/or try to destruct shared synchronization objects linked with
  ///     DB or LCK-file. Moreover, the implementation MUST ensure correct work
  ///     of other instances of MDBX_env within the current process, e.g.
  ///     restore POSIX-fcntl locks after the closing of file descriptors.
  /// \return Error code (MDBX_PANIC) or zero on success.
  MDBX_INTERNAL_FUNC int mdbx_lck_destroy(MDBX_env *env,
                                          MDBX_env *inprocess_neighbor);
  
  /// \brief Connects to shared interprocess locking objects and tries to acquire
  ///   the maximum lock level (shared if exclusive is not available)
  ///   Depending on implementation or/and platform (Windows) this function may
  ///   acquire the non-OS super-level lock (e.g. for shared synchronization
  ///   objects initialization), which will be downgraded to OS-exclusive or
  ///   shared via explicit calling of mdbx_lck_downgrade().
  /// \return
  ///   MDBX_RESULT_TRUE (-1) - if an exclusive lock was acquired and thus
  ///     the current process is the first and only after the last use of DB.
  ///   MDBX_RESULT_FALSE (0) - if a shared lock was acquired and thus
  ///     DB has already been opened and now is used by other processes.
  ///   Otherwise (not 0 and not -1) - error code.
  MDBX_INTERNAL_FUNC int mdbx_lck_seize(MDBX_env *env);
  
  /// \brief Downgrades the level of initially acquired lock to
  ///   operational level specified by argument. The reson for such downgrade:
  ///    - unblocking of other processes that are waiting for access, i.e.
  ///      if (env->me_flags & MDBX_EXCLUSIVE) != 0, then other processes
  ///      should be made aware that access is unavailable rather than
  ///      wait for it.
  ///    - freeing locks that interfere file operation (especially for Windows)
  ///   (env->me_flags & MDBX_EXCLUSIVE) == 0 - downgrade to shared lock.
  ///   (env->me_flags & MDBX_EXCLUSIVE) != 0 - downgrade to exclusive
  ///   operational lock.
  /// \return Error code or zero on success
  MDBX_INTERNAL_FUNC int mdbx_lck_downgrade(MDBX_env *env);
  
  /// \brief Locks LCK-file or/and table of readers for (de)registering.
  /// \return Error code or zero on success
  MDBX_INTERNAL_FUNC int mdbx_rdt_lock(MDBX_env *env);
  
  /// \brief Unlocks LCK-file or/and table of readers after (de)registering.
  MDBX_INTERNAL_FUNC void mdbx_rdt_unlock(MDBX_env *env);
  
  /// \brief Acquires lock for DB change (on writing transaction start)
  ///   Reading transactions will not be blocked.
  ///   Declared as LIBMDBX_API because it is used in mdbx_chk.
  /// \return Error code or zero on success
  LIBMDBX_API int mdbx_txn_lock(MDBX_env *env, bool dont_wait);
  
  /// \brief Releases lock once DB changes is made (after writing transaction
  ///   has finished).
  ///   Declared as LIBMDBX_API because it is used in mdbx_chk.
  LIBMDBX_API void mdbx_txn_unlock(MDBX_env *env);
  
  /// \brief Sets alive-flag of reader presence (indicative lock) for PID of
  ///   the current process. The function does no more than needed for
  ///   the correct working of mdbx_rpid_check() in other processes.
  /// \return Error code or zero on success
  MDBX_INTERNAL_FUNC int mdbx_rpid_set(MDBX_env *env);
  
  /// \brief Resets alive-flag of reader presence (indicative lock)
  ///   for PID of the current process. The function does no more than needed
  ///   for the correct working of mdbx_rpid_check() in other processes.
  /// \return Error code or zero on success
  MDBX_INTERNAL_FUNC int mdbx_rpid_clear(MDBX_env *env);
  
  /// \brief Checks for reading process status with the given pid with help of
  ///   alive-flag of presence (indicative lock) or using another way.
  /// \return
  ///   MDBX_RESULT_TRUE (-1) - if the reader process with the given PID is alive
  ///     and working with DB (indicative lock is present).
  ///   MDBX_RESULT_FALSE (0) - if the reader process with the given PID is absent
  ///     or not working with DB (indicative lock is not present).
  ///   Otherwise (not 0 and not -1) - error code.
  MDBX_INTERNAL_FUNC int mdbx_rpid_check(MDBX_env *env, uint32_t pid);
  
  #if defined(_WIN32) || defined(_WIN64)
  
  typedef void(WINAPI *MDBX_srwlock_function)(MDBX_srwlock *);
  MDBX_INTERNAL_VAR MDBX_srwlock_function mdbx_srwlock_Init,
      mdbx_srwlock_AcquireShared, mdbx_srwlock_ReleaseShared,
      mdbx_srwlock_AcquireExclusive, mdbx_srwlock_ReleaseExclusive;
  
  typedef BOOL(WINAPI *MDBX_GetFileInformationByHandleEx)(
      _In_ HANDLE hFile, _In_ FILE_INFO_BY_HANDLE_CLASS FileInformationClass,
      _Out_ LPVOID lpFileInformation, _In_ DWORD dwBufferSize);
  MDBX_INTERNAL_VAR MDBX_GetFileInformationByHandleEx
      mdbx_GetFileInformationByHandleEx;
  
  typedef BOOL(WINAPI *MDBX_GetVolumeInformationByHandleW)(
      _In_ HANDLE hFile, _Out_opt_ LPWSTR lpVolumeNameBuffer,
      _In_ DWORD nVolumeNameSize, _Out_opt_ LPDWORD lpVolumeSerialNumber,
      _Out_opt_ LPDWORD lpMaximumComponentLength,
      _Out_opt_ LPDWORD lpFileSystemFlags,
      _Out_opt_ LPWSTR lpFileSystemNameBuffer, _In_ DWORD nFileSystemNameSize);
  MDBX_INTERNAL_VAR MDBX_GetVolumeInformationByHandleW
      mdbx_GetVolumeInformationByHandleW;
  
  typedef DWORD(WINAPI *MDBX_GetFinalPathNameByHandleW)(_In_ HANDLE hFile,
                                                        _Out_ LPWSTR lpszFilePath,
                                                        _In_ DWORD cchFilePath,
                                                        _In_ DWORD dwFlags);
  MDBX_INTERNAL_VAR MDBX_GetFinalPathNameByHandleW mdbx_GetFinalPathNameByHandleW;
  
  typedef BOOL(WINAPI *MDBX_SetFileInformationByHandle)(
      _In_ HANDLE hFile, _In_ FILE_INFO_BY_HANDLE_CLASS FileInformationClass,
      _Out_ LPVOID lpFileInformation, _In_ DWORD dwBufferSize);
  MDBX_INTERNAL_VAR MDBX_SetFileInformationByHandle
      mdbx_SetFileInformationByHandle;
  
  typedef NTSTATUS(NTAPI *MDBX_NtFsControlFile)(
      IN HANDLE FileHandle, IN OUT HANDLE Event,
      IN OUT PVOID /* PIO_APC_ROUTINE */ ApcRoutine, IN OUT PVOID ApcContext,
      OUT PIO_STATUS_BLOCK IoStatusBlock, IN ULONG FsControlCode,
      IN OUT PVOID InputBuffer, IN ULONG InputBufferLength,
      OUT OPTIONAL PVOID OutputBuffer, IN ULONG OutputBufferLength);
  MDBX_INTERNAL_VAR MDBX_NtFsControlFile mdbx_NtFsControlFile;
  
  typedef uint64_t(WINAPI *MDBX_GetTickCount64)(void);
  MDBX_INTERNAL_VAR MDBX_GetTickCount64 mdbx_GetTickCount64;
  
  #if !defined(_WIN32_WINNT_WIN8) || _WIN32_WINNT < _WIN32_WINNT_WIN8
  typedef struct _WIN32_MEMORY_RANGE_ENTRY {
    PVOID VirtualAddress;
    SIZE_T NumberOfBytes;
  } WIN32_MEMORY_RANGE_ENTRY, *PWIN32_MEMORY_RANGE_ENTRY;
  #endif /* Windows 8.x */
  
  typedef BOOL(WINAPI *MDBX_PrefetchVirtualMemory)(
      HANDLE hProcess, ULONG_PTR NumberOfEntries,
      PWIN32_MEMORY_RANGE_ENTRY VirtualAddresses, ULONG Flags);
  MDBX_INTERNAL_VAR MDBX_PrefetchVirtualMemory mdbx_PrefetchVirtualMemory;
  
  #if 0 /* LY: unused for now */
  #if !defined(_WIN32_WINNT_WIN81) || _WIN32_WINNT < _WIN32_WINNT_WIN81
  typedef enum OFFER_PRIORITY {
    VmOfferPriorityVeryLow = 1,
    VmOfferPriorityLow,
    VmOfferPriorityBelowNormal,
    VmOfferPriorityNormal
  } OFFER_PRIORITY;
  #endif /* Windows 8.1 */
  
  typedef DWORD(WINAPI *MDBX_DiscardVirtualMemory)(PVOID VirtualAddress,
                                                   SIZE_T Size);
  MDBX_INTERNAL_VAR MDBX_DiscardVirtualMemory mdbx_DiscardVirtualMemory;
  
  typedef DWORD(WINAPI *MDBX_ReclaimVirtualMemory)(PVOID VirtualAddress,
                                                   SIZE_T Size);
  MDBX_INTERNAL_VAR MDBX_ReclaimVirtualMemory mdbx_ReclaimVirtualMemory;
  
  typedef DWORD(WINAPI *MDBX_OfferVirtualMemory(
    PVOID          VirtualAddress,
    SIZE_T         Size,
    OFFER_PRIORITY Priority
  );
  MDBX_INTERNAL_VAR MDBX_OfferVirtualMemory mdbx_OfferVirtualMemory;
  #endif /* unused for now */
  
  typedef enum _SECTION_INHERIT { ViewShare = 1, ViewUnmap = 2 } SECTION_INHERIT;
  
  typedef NTSTATUS(NTAPI *MDBX_NtExtendSection)(IN HANDLE SectionHandle,
                                                IN PLARGE_INTEGER NewSectionSize);
  MDBX_INTERNAL_VAR MDBX_NtExtendSection mdbx_NtExtendSection;
  
  static __inline bool mdbx_RunningUnderWine(void) {
    return !mdbx_NtExtendSection;
  }
  
  typedef LSTATUS(WINAPI *MDBX_RegGetValueA)(HKEY hkey, LPCSTR lpSubKey,
                                             LPCSTR lpValue, DWORD dwFlags,
                                             LPDWORD pdwType, PVOID pvData,
                                             LPDWORD pcbData);
  MDBX_INTERNAL_VAR MDBX_RegGetValueA mdbx_RegGetValueA;
  
  #endif /* Windows */
  
  #endif /* !__cplusplus */
  
  /*----------------------------------------------------------------------------*/
  
  #if defined(_MSC_VER) && _MSC_VER >= 1900
  /* LY: MSVC 2015/2017/2019 has buggy/inconsistent PRIuPTR/PRIxPTR macros
   * for internal format-args checker. */
  #undef PRIuPTR
  #undef PRIiPTR
  #undef PRIdPTR
  #undef PRIxPTR
  #define PRIuPTR "Iu"
  #define PRIiPTR "Ii"
  #define PRIdPTR "Id"
  #define PRIxPTR "Ix"
  #define PRIuSIZE "zu"
  #define PRIiSIZE "zi"
  #define PRIdSIZE "zd"
  #define PRIxSIZE "zx"
  #endif /* fix PRI*PTR for _MSC_VER */
  
  #ifndef PRIuSIZE
  #define PRIuSIZE PRIuPTR
  #define PRIiSIZE PRIiPTR
  #define PRIdSIZE PRIdPTR
  #define PRIxSIZE PRIxPTR
  #endif /* PRI*SIZE macros for MSVC */
  
  #ifdef _MSC_VER
  #pragma warning(pop)
  #endif
  
  #define mdbx_sourcery_anchor XCONCAT(mdbx_sourcery_, MDBX_BUILD_SOURCERY)
  #if defined(MDBX_TOOLS)
  extern LIBMDBX_API const char *const mdbx_sourcery_anchor;
  #endif
  
  /*******************************************************************************
   *******************************************************************************
   *******************************************************************************
   *
   *
   *         ####   #####    #####     #     ####   #    #   ####
   *        #    #  #    #     #       #    #    #  ##   #  #
   *        #    #  #    #     #       #    #    #  # #  #   ####
   *        #    #  #####      #       #    #    #  #  # #       #
   *        #    #  #          #       #    #    #  #   ##  #    #
   *         ####   #          #       #     ####   #    #   ####
   *
   *
   */
  
  /** \defgroup build_option Build options
   * The libmdbx build options.
   @{ */
  
  #ifdef DOXYGEN
  /* !!! Actually this is a fake definitions     !!!
   * !!! for documentation generation by Doxygen !!! */
  
  /** Controls enabling of debugging features.
   *
   *  - `MDBX_DEBUG = 0` (by default) Disables any debugging features at all,
   *                     including logging and assertion controls.
   *                     Logging level and corresponding debug flags changing
   *                     by \ref mdbx_setup_debug() will not have effect.
   *  - `MDBX_DEBUG > 0` Enables code for the debugging features (logging,
   *                     assertions checking and internal audit).
   *                     Simultaneously sets the default logging level
   *                     to the `MDBX_DEBUG` value.
   *                     Also enables \ref MDBX_DBG_AUDIT if `MDBX_DEBUG >= 2`.
   *
   * \ingroup build_option */
  #define MDBX_DEBUG 0...7
  
  /** Disables using of GNU libc extensions. */
  #define MDBX_DISABLE_GNU_SOURCE 0 or 1
  
  #endif /* DOXYGEN */
  
  /** Enables support for huge write-transactions */
  #ifndef MDBX_HUGE_TRANSACTIONS
  #define MDBX_HUGE_TRANSACTIONS 0
  #endif /* MDBX_HUGE_TRANSACTIONS */
  
  /** Using fcntl(F_FULLFSYNC) with 5-10 times slowdown */
  #define MDBX_OSX_WANNA_DURABILITY 0
  /** Using fsync() with chance of data lost on power failure */
  #define MDBX_OSX_WANNA_SPEED 1
  
  #ifndef MDBX_OSX_SPEED_INSTEADOF_DURABILITY
  /** Choices \ref MDBX_OSX_WANNA_DURABILITY or \ref MDBX_OSX_WANNA_SPEED
   * for OSX & iOS */
  #define MDBX_OSX_SPEED_INSTEADOF_DURABILITY MDBX_OSX_WANNA_DURABILITY
  #endif /* MDBX_OSX_SPEED_INSTEADOF_DURABILITY */
  
  /** Controls checking PID against reuse DB environment after the fork() */
  #ifndef MDBX_ENV_CHECKPID
  #if defined(MADV_DONTFORK) || defined(_WIN32) || defined(_WIN64)
  /* PID check could be omitted:
   *  - on Linux when madvise(MADV_DONTFORK) is available, i.e. after the fork()
   *    mapped pages will not be available for child process.
   *  - in Windows where fork() not available. */
  #define MDBX_ENV_CHECKPID 0
  #else
  #define MDBX_ENV_CHECKPID 1
  #endif
  #define MDBX_ENV_CHECKPID_CONFIG "AUTO=" STRINGIFY(MDBX_ENV_CHECKPID)
  #else
  #define MDBX_ENV_CHECKPID_CONFIG STRINGIFY(MDBX_ENV_CHECKPID)
  #endif /* MDBX_ENV_CHECKPID */
  
  /** Controls checking transaction owner thread against misuse transactions from
   * other threads. */
  #ifndef MDBX_TXN_CHECKOWNER
  #define MDBX_TXN_CHECKOWNER 1
  #define MDBX_TXN_CHECKOWNER_CONFIG "AUTO=" STRINGIFY(MDBX_TXN_CHECKOWNER)
  #else
  #define MDBX_TXN_CHECKOWNER_CONFIG STRINGIFY(MDBX_TXN_CHECKOWNER)
  #endif /* MDBX_TXN_CHECKOWNER */
  
  /** Does a system have battery-backed Real-Time Clock or just a fake. */
  #ifndef MDBX_TRUST_RTC
  #if defined(__linux__) || defined(__gnu_linux__) || defined(__NetBSD__) ||     \
      defined(__OpenBSD__)
  #define MDBX_TRUST_RTC 0 /* a lot of embedded systems have a fake RTC */
  #else
  #define MDBX_TRUST_RTC 1
  #endif
  #define MDBX_TRUST_RTC_CONFIG "AUTO=" STRINGIFY(MDBX_TRUST_RTC)
  #else
  #define MDBX_TRUST_RTC_CONFIG STRINGIFY(MDBX_TRUST_RTC)
  #endif /* MDBX_TRUST_RTC */
  
  //------------------------------------------------------------------------------
  
  /** Win32 File Locking API for \ref MDBX_LOCKING */
  #define MDBX_LOCKING_WIN32FILES -1
  
  /** SystemV IPC semaphores for \ref MDBX_LOCKING */
  #define MDBX_LOCKING_SYSV 5
  
  /** POSIX-1 Shared anonymous semaphores for \ref MDBX_LOCKING */
  #define MDBX_LOCKING_POSIX1988 1988
  
  /** POSIX-2001 Shared Mutexes for \ref MDBX_LOCKING */
  #define MDBX_LOCKING_POSIX2001 2001
  
  /** POSIX-2008 Robust Mutexes for \ref MDBX_LOCKING */
  #define MDBX_LOCKING_POSIX2008 2008
  
  /** BeOS Benaphores, aka Futexes for \ref MDBX_LOCKING */
  #define MDBX_LOCKING_BENAPHORE 1995
  
  /** Advanced: Choices the locking implementation (autodetection by default). */
  #if defined(_WIN32) || defined(_WIN64)
  #define MDBX_LOCKING MDBX_LOCKING_WIN32FILES
  #else
  #ifndef MDBX_LOCKING
  #if defined(_POSIX_THREAD_PROCESS_SHARED) &&                                   \
      _POSIX_THREAD_PROCESS_SHARED >= 200112L && !defined(__FreeBSD__)
  
  /* Some platforms define the EOWNERDEAD error code even though they
   * don't support Robust Mutexes. If doubt compile with -MDBX_LOCKING=2001. */
  #if defined(EOWNERDEAD) && _POSIX_THREAD_PROCESS_SHARED >= 200809L &&          \
      ((defined(_POSIX_THREAD_ROBUST_PRIO_INHERIT) &&                            \
        _POSIX_THREAD_ROBUST_PRIO_INHERIT > 0) ||                                \
       (defined(_POSIX_THREAD_ROBUST_PRIO_PROTECT) &&                            \
        _POSIX_THREAD_ROBUST_PRIO_PROTECT > 0) ||                                \
       defined(PTHREAD_MUTEX_ROBUST) || defined(PTHREAD_MUTEX_ROBUST_NP)) &&     \
      (!defined(__GLIBC__) ||                                                    \
       __GLIBC_PREREQ(2, 10) /* troubles with Robust mutexes before 2.10 */)
  #define MDBX_LOCKING MDBX_LOCKING_POSIX2008
  #else
  #define MDBX_LOCKING MDBX_LOCKING_POSIX2001
  #endif
  #elif defined(__sun) || defined(__SVR4) || defined(__svr4__)
  #define MDBX_LOCKING MDBX_LOCKING_POSIX1988
  #else
  #define MDBX_LOCKING MDBX_LOCKING_SYSV
  #endif
  #define MDBX_LOCKING_CONFIG "AUTO=" STRINGIFY(MDBX_LOCKING)
  #else
  #define MDBX_LOCKING_CONFIG STRINGIFY(MDBX_LOCKING)
  #endif /* MDBX_LOCKING */
  #endif /* !Windows */
  
  /** Advanced: Using POSIX OFD-locks (autodetection by default). */
  #ifndef MDBX_USE_OFDLOCKS
  #if defined(F_OFD_SETLK) && defined(F_OFD_SETLKW) && defined(F_OFD_GETLK) &&   \
      !defined(MDBX_SAFE4QEMU) &&                                                \
      !defined(__sun) /* OFD-lock are broken on Solaris */
  #define MDBX_USE_OFDLOCKS 1
  #else
  #define MDBX_USE_OFDLOCKS 0
  #endif
  #define MDBX_USE_OFDLOCKS_CONFIG "AUTO=" STRINGIFY(MDBX_USE_OFDLOCKS)
  #else
  #define MDBX_USE_OFDLOCKS_CONFIG STRINGIFY(MDBX_USE_OFDLOCKS)
  #endif /* MDBX_USE_OFDLOCKS */
  
  /** Advanced: Using sendfile() syscall (autodetection by default). */
  #ifndef MDBX_USE_SENDFILE
  #if ((defined(__linux__) || defined(__gnu_linux__)) &&                         \
       !defined(__ANDROID_API__)) ||                                             \
      (defined(__ANDROID_API__) && __ANDROID_API__ >= 21)
  #define MDBX_USE_SENDFILE 1
  #else
  #define MDBX_USE_SENDFILE 0
  #endif
  #endif /* MDBX_USE_SENDFILE */
  
  /** Advanced: Using copy_file_range() syscall (autodetection by default). */
  #ifndef MDBX_USE_COPYFILERANGE
  #if __GLIBC_PREREQ(2, 27) && defined(_GNU_SOURCE)
  #define MDBX_USE_COPYFILERANGE 1
  #else
  #define MDBX_USE_COPYFILERANGE 0
  #endif
  #endif /* MDBX_USE_COPYFILERANGE */
  
  /** Advanced: Using sync_file_range() syscall (autodetection by default). */
  #ifndef MDBX_USE_SYNCFILERANGE
  #if ((defined(__linux__) || defined(__gnu_linux__)) &&                         \
       defined(SYNC_FILE_RANGE_WRITE) && !defined(__ANDROID_API__)) ||           \
      (defined(__ANDROID_API__) && __ANDROID_API__ >= 26)
  #define MDBX_USE_SYNCFILERANGE 1
  #else
  #define MDBX_USE_SYNCFILERANGE 0
  #endif
  #endif /* MDBX_USE_SYNCFILERANGE */
  
  //------------------------------------------------------------------------------
  
  #ifndef MDBX_CPU_WRITEBACK_INCOHERENT
  #if defined(__ia32__) || defined(__e2k__) || defined(__hppa) ||                \
      defined(__hppa__) || defined(DOXYGEN)
  #define MDBX_CPU_WRITEBACK_INCOHERENT 0
  #else
  #define MDBX_CPU_WRITEBACK_INCOHERENT 1
  #endif
  #endif /* MDBX_CPU_WRITEBACK_INCOHERENT */
  
  #ifndef MDBX_MMAP_INCOHERENT_FILE_WRITE
  #ifdef __OpenBSD__
  #define MDBX_MMAP_INCOHERENT_FILE_WRITE 1
  #else
  #define MDBX_MMAP_INCOHERENT_FILE_WRITE 0
  #endif
  #endif /* MDBX_MMAP_INCOHERENT_FILE_WRITE */
  
  #ifndef MDBX_MMAP_INCOHERENT_CPU_CACHE
  #if defined(__mips) || defined(__mips__) || defined(__mips64) ||               \
      defined(__mips64__) || defined(_M_MRX000) || defined(_MIPS_) ||            \
      defined(__MWERKS__) || defined(__sgi)
  /* MIPS has cache coherency issues. */
  #define MDBX_MMAP_INCOHERENT_CPU_CACHE 1
  #else
  /* LY: assume no relevant mmap/dcache issues. */
  #define MDBX_MMAP_INCOHERENT_CPU_CACHE 0
  #endif
  #endif /* MDBX_MMAP_INCOHERENT_CPU_CACHE */
  
  #ifndef MDBX_64BIT_ATOMIC
  #if MDBX_WORDBITS >= 64 || defined(DOXYGEN)
  #define MDBX_64BIT_ATOMIC 1
  #else
  #define MDBX_64BIT_ATOMIC 0
  #endif
  #define MDBX_64BIT_ATOMIC_CONFIG "AUTO=" STRINGIFY(MDBX_64BIT_ATOMIC)
  #else
  #define MDBX_64BIT_ATOMIC_CONFIG STRINGIFY(MDBX_64BIT_ATOMIC)
  #endif /* MDBX_64BIT_ATOMIC */
  
  #ifndef MDBX_64BIT_CAS
  #if defined(ATOMIC_LLONG_LOCK_FREE)
  #if ATOMIC_LLONG_LOCK_FREE > 1
  #define MDBX_64BIT_CAS 1
  #else
  #define MDBX_64BIT_CAS 0
  #endif
  #elif defined(__GCC_ATOMIC_LLONG_LOCK_FREE)
  #if __GCC_ATOMIC_LLONG_LOCK_FREE > 1
  #define MDBX_64BIT_CAS 1
  #else
  #define MDBX_64BIT_CAS 0
  #endif
  #elif defined(__CLANG_ATOMIC_LLONG_LOCK_FREE)
  #if __CLANG_ATOMIC_LLONG_LOCK_FREE > 1
  #define MDBX_64BIT_CAS 1
  #else
  #define MDBX_64BIT_CAS 0
  #endif
  #elif defined(_MSC_VER) || defined(__APPLE__) || defined(DOXYGEN)
  #define MDBX_64BIT_CAS 1
  #else
  #define MDBX_64BIT_CAS MDBX_64BIT_ATOMIC
  #endif
  #define MDBX_64BIT_CAS_CONFIG "AUTO=" STRINGIFY(MDBX_64BIT_CAS)
  #else
  #define MDBX_64BIT_CAS_CONFIG STRINGIFY(MDBX_64BIT_CAS)
  #endif /* MDBX_64BIT_CAS */
  
  #if !defined(MDBX_UNALIGNED_OK)
  #if defined(_MSC_VER)
  #define MDBX_UNALIGNED_OK 1 /* avoid MSVC misoptimization */
  #elif __CLANG_PREREQ(5, 0) || __GNUC_PREREQ(5, 0)
  #define MDBX_UNALIGNED_OK 0 /* expecting optimization is well done */
  #elif (defined(__ia32__) || defined(__ARM_FEATURE_UNALIGNED)) &&               \
      !defined(__ALIGNED__)
  #define MDBX_UNALIGNED_OK 1
  #else
  #define MDBX_UNALIGNED_OK 0
  #endif
  #endif /* MDBX_UNALIGNED_OK */
  
  #ifndef MDBX_CACHELINE_SIZE
  #if defined(SYSTEM_CACHE_ALIGNMENT_SIZE)
  #define MDBX_CACHELINE_SIZE SYSTEM_CACHE_ALIGNMENT_SIZE
  #elif defined(__ia64__) || defined(__ia64) || defined(_M_IA64)
  #define MDBX_CACHELINE_SIZE 128
  #else
  #define MDBX_CACHELINE_SIZE 64
  #endif
  #endif /* MDBX_CACHELINE_SIZE */
  
  /** @} end of build options */
  /*******************************************************************************
   *******************************************************************************
   ******************************************************************************/
  
  /*----------------------------------------------------------------------------*/
  /* Basic constants and types */
  
  /* The minimum number of keys required in a database page.
   * Setting this to a larger value will place a smaller bound on the
   * maximum size of a data item. Data items larger than this size will
   * be pushed into overflow pages instead of being stored directly in
   * the B-tree node. This value used to default to 4. With a page size
   * of 4096 bytes that meant that any item larger than 1024 bytes would
   * go into an overflow page. That also meant that on average 2-3KB of
   * each overflow page was wasted space. The value cannot be lower than
   * 2 because then there would no longer be a tree structure. With this
   * value, items larger than 2KB will go into overflow pages, and on
   * average only 1KB will be wasted. */
  #define MDBX_MINKEYS 2
  
  /* A stamp that identifies a file as an MDBX file.
   * There's nothing special about this value other than that it is easily
   * recognizable, and it will reflect any byte order mismatches. */
  #define MDBX_MAGIC UINT64_C(/* 56-bit prime */ 0x59659DBDEF4C11)
  
  /* The version number for a database's datafile format. */
  #define MDBX_DATA_VERSION 2
  /* The version number for a database's lockfile format. */
  #define MDBX_LOCK_VERSION 3
  
  /* handle for the DB used to track free pages. */
  #define FREE_DBI 0
  /* handle for the default DB. */
  #define MAIN_DBI 1
  /* Number of DBs in metapage (free and main) - also hardcoded elsewhere */
  #define CORE_DBS 2
  
  /* Number of meta pages - also hardcoded elsewhere */
  #define NUM_METAS 3
  
  /* A page number in the database.
   *
   * MDBX uses 32 bit for page numbers. This limits database
   * size up to 2^44 bytes, in case of 4K pages. */
  typedef uint32_t pgno_t;
  #define PRIaPGNO PRIu32
  #define MAX_PAGENO UINT32_C(0x7FFFffff)
  #define MIN_PAGENO NUM_METAS
  
  #define SAFE64_INVALID_THRESHOLD UINT64_C(0xffffFFFF00000000)
  
  /* A transaction ID. */
  typedef uint64_t txnid_t;
  #define PRIaTXN PRIi64
  #define MIN_TXNID UINT64_C(1)
  #define MAX_TXNID (SAFE64_INVALID_THRESHOLD - 1)
  #define INITIAL_TXNID (MIN_TXNID + NUM_METAS - 1)
  #define INVALID_TXNID UINT64_MAX
  /* LY: for testing non-atomic 64-bit txnid on 32-bit arches.
   * #define MDBX_TXNID_STEP (UINT32_MAX / 3) */
  #ifndef MDBX_TXNID_STEP
  #if MDBX_64BIT_CAS
  #define MDBX_TXNID_STEP 1u
  #else
  #define MDBX_TXNID_STEP 2u
  #endif
  #endif /* MDBX_TXNID_STEP */
  
  /* Used for offsets within a single page.
   * Since memory pages are typically 4 or 8KB in size, 12-13 bits,
   * this is plenty. */
  typedef uint16_t indx_t;
  
  #define MEGABYTE ((size_t)1 << 20)
  
  /*----------------------------------------------------------------------------*/
  /* Core structures for database and shared memory (i.e. format definition) */
  #pragma pack(push, 1)
  
  typedef union mdbx_safe64 {
    volatile uint64_t inconsistent;
  #if MDBX_64BIT_ATOMIC
    volatile uint64_t atomic;
  #endif /* MDBX_64BIT_ATOMIC */
    __anonymous_struct_extension__ struct {
  #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
      volatile uint32_t low;
      volatile uint32_t high;
  #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
      volatile uint32_t high;
      volatile uint32_t low;
  #else
  #error "FIXME: Unsupported byte order"
  #endif /* __BYTE_ORDER__ */
    };
  } mdbx_safe64_t;
  
  /* Information about a single database in the environment. */
  typedef struct MDBX_db {
    uint16_t md_flags;        /* see mdbx_dbi_open */
    uint16_t md_depth;        /* depth of this tree */
    uint32_t md_xsize;        /* key-size for MDBX_DUPFIXED (LEAF2 pages) */
    pgno_t md_root;           /* the root page of this tree */
    pgno_t md_branch_pages;   /* number of internal pages */
    pgno_t md_leaf_pages;     /* number of leaf pages */
    pgno_t md_overflow_pages; /* number of overflow pages */
    uint64_t md_seq;          /* table sequence counter */
    uint64_t md_entries;      /* number of data items */
    uint64_t md_mod_txnid;    /* txnid of last committed modification */
  } MDBX_db;
  
  /* database size-related parameters */
  typedef struct mdbx_geo_t {
    uint16_t grow;   /* datafile growth step in pages */
    uint16_t shrink; /* datafile shrink threshold in pages */
    pgno_t lower;    /* minimal size of datafile in pages */
    pgno_t upper;    /* maximal size of datafile in pages */
    pgno_t now;      /* current size of datafile in pages */
    pgno_t next;     /* first unused page in the datafile,
                      * but actually the file may be shorter. */
  } mdbx_geo_t;
  
  /* Meta page content.
   * A meta page is the start point for accessing a database snapshot.
   * Pages 0-1 are meta pages. Transaction N writes meta page (N % 2). */
  typedef struct MDBX_meta {
    /* Stamp identifying this as an MDBX file.
     * It must be set to MDBX_MAGIC with MDBX_DATA_VERSION. */
    uint64_t mm_magic_and_version;
  
    /* txnid that committed this page, the first of a two-phase-update pair */
    mdbx_safe64_t mm_txnid_a;
  
    uint16_t mm_extra_flags;  /* extra DB flags, zero (nothing) for now */
    uint8_t mm_validator_id;  /* ID of checksum and page validation method,
                               * zero (nothing) for now */
    uint8_t mm_extra_pagehdr; /* extra bytes in the page header,
                               * zero (nothing) for now */
  
    mdbx_geo_t mm_geo; /* database size-related parameters */
  
    MDBX_db mm_dbs[CORE_DBS]; /* first is free space, 2nd is main db */
                              /* The size of pages used in this DB */
  #define mm_psize mm_dbs[FREE_DBI].md_xsize
  /* Any persistent environment flags, see mdbx_env */
  #define mm_flags mm_dbs[FREE_DBI].md_flags
    MDBX_canary mm_canary;
  
  #define MDBX_DATASIGN_NONE 0u
  #define MDBX_DATASIGN_WEAK 1u
  #define SIGN_IS_STEADY(sign) ((sign) > MDBX_DATASIGN_WEAK)
  #define META_IS_STEADY(meta) SIGN_IS_STEADY((meta)->mm_datasync_sign)
    volatile uint64_t mm_datasync_sign;
  
    /* txnid that committed this page, the second of a two-phase-update pair */
    mdbx_safe64_t mm_txnid_b;
  
    /* Number of non-meta pages which were put in GC after COW. May be 0 in case
     * DB was previously handled by libmdbx without corresponding feature.
     * This value in couple with mr_snapshot_pages_retired allows fast estimation
     * of "how much reader is restraining GC recycling". */
    uint64_t mm_pages_retired;
  
    /* The analogue /proc/sys/kernel/random/boot_id or similar to determine
     * whether the system was rebooted after the last use of the database files.
     * If there was no reboot, but there is no need to rollback to the last
     * steady sync point. Zeros mean that no relevant information is available
     * from the system. */
    bin128_t mm_bootid;
  
  } MDBX_meta;
  
  /* Common header for all page types. The page type depends on mp_flags.
   *
   * P_BRANCH and P_LEAF pages have unsorted 'MDBX_node's at the end, with
   * sorted mp_ptrs[] entries referring to them. Exception: P_LEAF2 pages
   * omit mp_ptrs and pack sorted MDBX_DUPFIXED values after the page header.
   *
   * P_OVERFLOW records occupy one or more contiguous pages where only the
   * first has a page header. They hold the real data of F_BIGDATA nodes.
   *
   * P_SUBP sub-pages are small leaf "pages" with duplicate data.
   * A node with flag F_DUPDATA but not F_SUBDATA contains a sub-page.
   * (Duplicate data can also go in sub-databases, which use normal pages.)
   *
   * P_META pages contain MDBX_meta, the start point of an MDBX snapshot.
   *
   * Each non-metapage up to MDBX_meta.mm_last_pg is reachable exactly once
   * in the snapshot: Either used by a database or listed in a GC record. */
  typedef struct MDBX_page {
    union {
      struct MDBX_page *mp_next; /* for in-memory list of freed pages */
      uint64_t mp_txnid;         /* txnid that committed this page */
    };
    uint16_t mp_leaf2_ksize; /* key size if this is a LEAF2 page */
  #define P_BRANCH 0x01      /* branch page */
  #define P_LEAF 0x02        /* leaf page */
  #define P_OVERFLOW 0x04    /* overflow page */
  #define P_META 0x08        /* meta page */
  #define P_DIRTY 0x10       /* dirty page, also set for P_SUBP pages */
  #define P_LEAF2 0x20       /* for MDBX_DUPFIXED records */
  #define P_SUBP 0x40        /* for MDBX_DUPSORT sub-pages */
  #define P_LOOSE 0x4000     /* page was dirtied then freed, can be reused */
  #define P_KEEP 0x8000      /* leave this page alone during spill */
    uint16_t mp_flags;
    union {
      __anonymous_struct_extension__ struct {
        indx_t mp_lower; /* lower bound of free space */
        indx_t mp_upper; /* upper bound of free space */
      };
      uint32_t mp_pages; /* number of overflow pages */
    };
    pgno_t mp_pgno; /* page number */
  
  #if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
      (!defined(__cplusplus) && defined(_MSC_VER))
    indx_t mp_ptrs[] /* dynamic size */;
  #endif /* C99 */
  } MDBX_page;
  
  /* Size of the page header, excluding dynamic data at the end */
  #define PAGEHDRSZ ((unsigned)offsetof(MDBX_page, mp_ptrs))
  
  #pragma pack(pop)
  
  #if MDBX_LOCKING == MDBX_LOCKING_WIN32FILES
  #define MDBX_CLOCK_SIGN UINT32_C(0xF10C)
  typedef void mdbx_ipclock_t;
  #elif MDBX_LOCKING == MDBX_LOCKING_SYSV
  
  #define MDBX_CLOCK_SIGN UINT32_C(0xF18D)
  typedef mdbx_pid_t mdbx_ipclock_t;
  #ifndef EOWNERDEAD
  #define EOWNERDEAD MDBX_RESULT_TRUE
  #endif
  
  #elif MDBX_LOCKING == MDBX_LOCKING_POSIX2001 ||                                \
      MDBX_LOCKING == MDBX_LOCKING_POSIX2008
  #define MDBX_CLOCK_SIGN UINT32_C(0x8017)
  typedef pthread_mutex_t mdbx_ipclock_t;
  #elif MDBX_LOCKING == MDBX_LOCKING_POSIX1988
  #define MDBX_CLOCK_SIGN UINT32_C(0xFC29)
  typedef sem_t mdbx_ipclock_t;
  #else
  #error "FIXME"
  #endif /* MDBX_LOCKING */
  
  #if MDBX_LOCKING > MDBX_LOCKING_SYSV && !defined(__cplusplus)
  MDBX_INTERNAL_FUNC int mdbx_ipclock_stub(mdbx_ipclock_t *ipc);
  MDBX_INTERNAL_FUNC int mdbx_ipclock_destroy(mdbx_ipclock_t *ipc);
  #endif /* MDBX_LOCKING */
  
  /* Reader Lock Table
   *
   * Readers don't acquire any locks for their data access. Instead, they
   * simply record their transaction ID in the reader table. The reader
   * mutex is needed just to find an empty slot in the reader table. The
   * slot's address is saved in thread-specific data so that subsequent
   * read transactions started by the same thread need no further locking to
   * proceed.
   *
   * If MDBX_NOTLS is set, the slot address is not saved in thread-specific data.
   * No reader table is used if the database is on a read-only filesystem.
   *
   * Since the database uses multi-version concurrency control, readers don't
   * actually need any locking. This table is used to keep track of which
   * readers are using data from which old transactions, so that we'll know
   * when a particular old transaction is no longer in use. Old transactions
   * that have discarded any data pages can then have those pages reclaimed
   * for use by a later write transaction.
   *
   * The lock table is constructed such that reader slots are aligned with the
   * processor's cache line size. Any slot is only ever used by one thread.
   * This alignment guarantees that there will be no contention or cache
   * thrashing as threads update their own slot info, and also eliminates
   * any need for locking when accessing a slot.
   *
   * A writer thread will scan every slot in the table to determine the oldest
   * outstanding reader transaction. Any freed pages older than this will be
   * reclaimed by the writer. The writer doesn't use any locks when scanning
   * this table. This means that there's no guarantee that the writer will
   * see the most up-to-date reader info, but that's not required for correct
   * operation - all we need is to know the upper bound on the oldest reader,
   * we don't care at all about the newest reader. So the only consequence of
   * reading stale information here is that old pages might hang around a
   * while longer before being reclaimed. That's actually good anyway, because
   * the longer we delay reclaiming old pages, the more likely it is that a
   * string of contiguous pages can be found after coalescing old pages from
   * many old transactions together. */
  
  /* The actual reader record, with cacheline padding. */
  typedef struct MDBX_reader {
    /* Current Transaction ID when this transaction began, or (txnid_t)-1.
     * Multiple readers that start at the same time will probably have the
     * same ID here. Again, it's not important to exclude them from
     * anything; all we need to know is which version of the DB they
     * started from so we can avoid overwriting any data used in that
     * particular version. */
    mdbx_safe64_t /* txnid_t */ mr_txnid;
  
    /* The information we store in a single slot of the reader table.
     * In addition to a transaction ID, we also record the process and
     * thread ID that owns a slot, so that we can detect stale information,
     * e.g. threads or processes that went away without cleaning up.
     *
     * NOTE: We currently don't check for stale records.
     * We simply re-init the table when we know that we're the only process
     * opening the lock file. */
  
    /* The thread ID of the thread owning this txn. */
  #if MDBX_WORDBITS >= 64
    volatile uint64_t mr_tid;
  #else
    volatile uint32_t mr_tid;
    volatile uint32_t mr_aba_curer; /* CSN to resolve ABA_problems on 32-bit arch,
                                       unused for now */
  #endif
    /* The process ID of the process owning this reader txn. */
    volatile uint32_t mr_pid;
  
    /* The number of pages used in the reader's MVCC snapshot,
     * i.e. the value of meta->mm_geo.next and txn->mt_next_pgno */
    volatile pgno_t mr_snapshot_pages_used;
    /* Number of retired pages at the time this reader starts transaction. So,
     * at any time the difference mm_pages_retired - mr_snapshot_pages_retired
     * will give the number of pages which this reader restraining from reuse. */
    volatile uint64_t mr_snapshot_pages_retired;
  } MDBX_reader;
  
  /* The header for the reader table (a memory-mapped lock file). */
  typedef struct MDBX_lockinfo {
    /* Stamp identifying this as an MDBX file.
     * It must be set to MDBX_MAGIC with with MDBX_LOCK_VERSION. */
    uint64_t mti_magic_and_version;
  
    /* Format of this lock file. Must be set to MDBX_LOCK_FORMAT. */
    uint32_t mti_os_and_format;
  
    /* Flags which environment was opened. */
    volatile uint32_t mti_envmode;
  
    /* Threshold of un-synced-with-disk pages for auto-sync feature,
     * zero means no-threshold, i.e. auto-sync is disabled. */
    volatile pgno_t mti_autosync_threshold;
  
    /* Low 32-bit of txnid with which meta-pages was synced,
     * i.e. for sync-polling in the MDBX_NOMETASYNC mode. */
    volatile uint32_t mti_meta_sync_txnid;
  
    /* Period for timed auto-sync feature, i.e. at the every steady checkpoint
     * the mti_unsynced_timeout sets to the current_time + mti_autosync_period.
     * The time value is represented in a suitable system-dependent form, for
     * example clock_gettime(CLOCK_BOOTTIME) or clock_gettime(CLOCK_MONOTONIC).
     * Zero means timed auto-sync is disabled. */
    volatile uint64_t mti_autosync_period;
  
    /* Marker to distinguish uniqueness of DB/CLK.*/
    volatile uint64_t mti_bait_uniqueness;
  
    alignas(MDBX_CACHELINE_SIZE) /* cacheline ---------------------------------*/
  
    /* Write transaction lock. */
  #if MDBX_LOCKING > 0
        mdbx_ipclock_t mti_wlock;
  #endif /* MDBX_LOCKING > 0 */
  
    volatile txnid_t mti_oldest_reader;
  
    /* Timestamp of the last steady sync. Value is represented in a suitable
     * system-dependent form, for example clock_gettime(CLOCK_BOOTTIME) or
     * clock_gettime(CLOCK_MONOTONIC). */
    volatile uint64_t mti_sync_timestamp;
  
    /* Number un-synced-with-disk pages for auto-sync feature. */
    volatile pgno_t mti_unsynced_pages;
  
    /* Number of page which was discarded last time by madvise(MADV_FREE). */
    volatile pgno_t mti_discarded_tail;
  
    /* Timestamp of the last readers check. */
    volatile uint64_t mti_reader_check_timestamp;
  
    alignas(MDBX_CACHELINE_SIZE) /* cacheline ---------------------------------*/
  
    /* Readeaders registration lock. */
  #if MDBX_LOCKING > 0
        mdbx_ipclock_t mti_rlock;
  #endif /* MDBX_LOCKING > 0 */
  
    /* The number of slots that have been used in the reader table.
     * This always records the maximum count, it is not decremented
     * when readers release their slots. */
    volatile unsigned mti_numreaders;
    volatile unsigned mti_readers_refresh_flag;
  
  #if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
      (!defined(__cplusplus) && defined(_MSC_VER))
    alignas(MDBX_CACHELINE_SIZE) /* cacheline ---------------------------------*/
        MDBX_reader mti_readers[] /* dynamic size */;
  #endif /* C99 */
  } MDBX_lockinfo;
  
  /* Lockfile format signature: version, features and field layout */
  #define MDBX_LOCK_FORMAT                                                       \
    (MDBX_CLOCK_SIGN * 27733 + (unsigned)sizeof(MDBX_reader) * 13 +              \
     (unsigned)offsetof(MDBX_reader, mr_snapshot_pages_used) * 251 +             \
     (unsigned)offsetof(MDBX_lockinfo, mti_oldest_reader) * 83 +                 \
     (unsigned)offsetof(MDBX_lockinfo, mti_numreaders) * 37 +                    \
     (unsigned)offsetof(MDBX_lockinfo, mti_readers) * 29)
  
  #define MDBX_DATA_MAGIC ((MDBX_MAGIC << 8) + MDBX_DATA_VERSION)
  #define MDBX_DATA_MAGIC_DEVEL ((MDBX_MAGIC << 8) + 255)
  
  #define MDBX_LOCK_MAGIC ((MDBX_MAGIC << 8) + MDBX_LOCK_VERSION)
  
  #ifndef MDBX_ASSUME_MALLOC_OVERHEAD
  #define MDBX_ASSUME_MALLOC_OVERHEAD (sizeof(void *) * 2u)
  #endif /* MDBX_ASSUME_MALLOC_OVERHEAD */
  
  /* The maximum size of a database page.
   *
   * It is 64K, but value-PAGEHDRSZ must fit in MDBX_page.mp_upper.
   *
   * MDBX will use database pages < OS pages if needed.
   * That causes more I/O in write transactions: The OS must
   * know (read) the whole page before writing a partial page.
   *
   * Note that we don't currently support Huge pages. On Linux,
   * regular data files cannot use Huge pages, and in general
   * Huge pages aren't actually pageable. We rely on the OS
   * demand-pager to read our data and page it out when memory
   * pressure from other processes is high. So until OSs have
   * actual paging support for Huge pages, they're not viable. */
  #define MAX_PAGESIZE MDBX_MAX_PAGESIZE
  #define MIN_PAGESIZE MDBX_MIN_PAGESIZE
  
  #define MIN_MAPSIZE (MIN_PAGESIZE * MIN_PAGENO)
  #if defined(_WIN32) || defined(_WIN64)
  #define MAX_MAPSIZE32 UINT32_C(0x38000000)
  #else
  #define MAX_MAPSIZE32 UINT32_C(0x7f000000)
  #endif
  #define MAX_MAPSIZE64 (MAX_PAGENO * (uint64_t)MAX_PAGESIZE)
  
  #if MDBX_WORDBITS >= 64
  #define MAX_MAPSIZE MAX_MAPSIZE64
  #define MDBX_READERS_LIMIT                                                     \
    ((65536 - sizeof(MDBX_lockinfo)) / sizeof(MDBX_reader))
  #else
  #define MDBX_READERS_LIMIT 1024
  #define MAX_MAPSIZE MAX_MAPSIZE32
  #endif /* MDBX_WORDBITS */
  
  /*----------------------------------------------------------------------------*/
  /* Two kind lists of pages (aka PNL) */
  
  /* An PNL is an Page Number List, a sorted array of IDs. The first element of
   * the array is a counter for how many actual page-numbers are in the list.
   * PNLs are sorted in descending order, this allow cut off a page with lowest
   * pgno (at the tail) just truncating the list */
  #define MDBX_PNL_ASCENDING 0
  typedef pgno_t *MDBX_PNL;
  
  #if MDBX_PNL_ASCENDING
  #define MDBX_PNL_ORDERED(first, last) ((first) < (last))
  #define MDBX_PNL_DISORDERED(first, last) ((first) >= (last))
  #else
  #define MDBX_PNL_ORDERED(first, last) ((first) > (last))
  #define MDBX_PNL_DISORDERED(first, last) ((first) <= (last))
  #endif
  
  /* List of txnid, only for MDBX_txn.tw.lifo_reclaimed */
  typedef txnid_t *MDBX_TXL;
  
  /* An Dirty-Page list item is an pgno/pointer pair. */
  typedef union MDBX_DP {
    __anonymous_struct_extension__ struct {
      pgno_t pgno;
      MDBX_page *ptr;
    };
    __anonymous_struct_extension__ struct {
      unsigned sorted;
      unsigned length;
    };
  } MDBX_DP;
  
  /* An DPL (dirty-page list) is a sorted array of MDBX_DPs.
   * The first element's length member is a count of how many actual
   * elements are in the array. */
  typedef MDBX_DP *MDBX_DPL;
  
  /* PNL sizes */
  #define MDBX_PNL_GRANULATE 1024
  #define MDBX_PNL_INITIAL                                                       \
    (MDBX_PNL_GRANULATE - 2 - MDBX_ASSUME_MALLOC_OVERHEAD / sizeof(pgno_t))
  
  #if MDBX_HUGE_TRANSACTIONS
  #define MDBX_PNL_MAX                                                           \
    ((1u << 26) - 2 - MDBX_ASSUME_MALLOC_OVERHEAD / sizeof(pgno_t))
  #define MDBX_DPL_TXNFULL (MDBX_PNL_MAX / 2)
  #else
  #define MDBX_PNL_MAX                                                           \
    ((1u << 24) - 2 - MDBX_ASSUME_MALLOC_OVERHEAD / sizeof(pgno_t))
  #define MDBX_DPL_TXNFULL (MDBX_PNL_MAX / 4)
  #endif /* MDBX_HUGE_TRANSACTIONS */
  
  #define MDBX_TXL_GRANULATE 32
  #define MDBX_TXL_INITIAL                                                       \
    (MDBX_TXL_GRANULATE - 2 - MDBX_ASSUME_MALLOC_OVERHEAD / sizeof(txnid_t))
  #define MDBX_TXL_MAX                                                           \
    ((1u << 17) - 2 - MDBX_ASSUME_MALLOC_OVERHEAD / sizeof(txnid_t))
  
  #define MDBX_PNL_ALLOCLEN(pl) ((pl)[-1])
  #define MDBX_PNL_SIZE(pl) ((pl)[0])
  #define MDBX_PNL_FIRST(pl) ((pl)[1])
  #define MDBX_PNL_LAST(pl) ((pl)[MDBX_PNL_SIZE(pl)])
  #define MDBX_PNL_BEGIN(pl) (&(pl)[1])
  #define MDBX_PNL_END(pl) (&(pl)[MDBX_PNL_SIZE(pl) + 1])
  
  #if MDBX_PNL_ASCENDING
  #define MDBX_PNL_LEAST(pl) MDBX_PNL_FIRST(pl)
  #define MDBX_PNL_MOST(pl) MDBX_PNL_LAST(pl)
  #else
  #define MDBX_PNL_LEAST(pl) MDBX_PNL_LAST(pl)
  #define MDBX_PNL_MOST(pl) MDBX_PNL_FIRST(pl)
  #endif
  
  #define MDBX_PNL_SIZEOF(pl) ((MDBX_PNL_SIZE(pl) + 1) * sizeof(pgno_t))
  #define MDBX_PNL_IS_EMPTY(pl) (MDBX_PNL_SIZE(pl) == 0)
  
  /*----------------------------------------------------------------------------*/
  /* Internal structures */
  
  /* Auxiliary DB info.
   * The information here is mostly static/read-only. There is
   * only a single copy of this record in the environment. */
  typedef struct MDBX_dbx {
    MDBX_val md_name;                /* name of the database */
    MDBX_cmp_func *md_cmp;           /* function for comparing keys */
    MDBX_cmp_func *md_dcmp;          /* function for comparing data items */
    size_t md_klen_min, md_klen_max; /* min/max key length for the database */
    size_t md_vlen_min,
        md_vlen_max; /* min/max value/data length for the database */
  } MDBX_dbx;
  
  /* A database transaction.
   * Every operation requires a transaction handle. */
  struct MDBX_txn {
  #define MDBX_MT_SIGNATURE UINT32_C(0x93D53A31)
    size_t mt_signature;
    MDBX_txn *mt_parent; /* parent of a nested txn */
    /* Nested txn under this txn, set together with flag MDBX_TXN_HAS_CHILD */
    MDBX_txn *mt_child;
    mdbx_geo_t mt_geo;
    /* next unallocated page */
  #define mt_next_pgno mt_geo.next
    /* corresponding to the current size of datafile */
  #define mt_end_pgno mt_geo.now
  
    /* Transaction Flags */
    /* mdbx_txn_begin() flags */
  #define MDBX_TXN_RO_BEGIN_FLAGS (MDBX_TXN_RDONLY | MDBX_TXN_RDONLY_PREPARE)
  #define MDBX_TXN_RW_BEGIN_FLAGS                                                \
    (MDBX_TXN_NOMETASYNC | MDBX_TXN_NOSYNC | MDBX_TXN_TRY)
    /* Additional flag for mdbx_sync_locked() */
  #define MDBX_SHRINK_ALLOWED UINT32_C(0x40000000)
  
    /* internal txn flags */
  #define MDBX_TXN_FINISHED 0x01  /* txn is finished or never began */
  #define MDBX_TXN_ERROR 0x02     /* txn is unusable after an error */
  #define MDBX_TXN_DIRTY 0x04     /* must write, even if dirty list is empty */
  #define MDBX_TXN_SPILLS 0x08    /* txn or a parent has spilled pages */
  #define MDBX_TXN_HAS_CHILD 0x10 /* txn has an MDBX_txn.mt_child */
    /* most operations on the txn are currently illegal */
  #define MDBX_TXN_BLOCKED                                                       \
    (MDBX_TXN_FINISHED | MDBX_TXN_ERROR | MDBX_TXN_HAS_CHILD)
  
  #define TXN_FLAGS                                                              \
    (MDBX_TXN_FINISHED | MDBX_TXN_ERROR | MDBX_TXN_DIRTY | MDBX_TXN_SPILLS |     \
     MDBX_TXN_HAS_CHILD)
  
  #if (TXN_FLAGS & (MDBX_TXN_RW_BEGIN_FLAGS | MDBX_TXN_RO_BEGIN_FLAGS)) ||       \
      ((MDBX_TXN_RW_BEGIN_FLAGS | MDBX_TXN_RO_BEGIN_FLAGS | TXN_FLAGS) &         \
       MDBX_SHRINK_ALLOWED)
  #error "Oops, some flags overlapped or wrong"
  #endif
  
    unsigned mt_flags;
    /* The ID of this transaction. IDs are integers incrementing from 1.
     * Only committed write transactions increment the ID. If a transaction
     * aborts, the ID may be re-used by the next writer. */
    txnid_t mt_txnid;
    MDBX_env *mt_env; /* the DB environment */
    /* Array of records for each DB known in the environment. */
    MDBX_dbx *mt_dbxs;
    /* Array of MDBX_db records for each known DB */
    MDBX_db *mt_dbs;
    /* Array of sequence numbers for each DB handle */
    unsigned *mt_dbiseqs;
  
    /* Transaction DBI Flags */
  #define DBI_DIRTY MDBX_DBI_DIRTY /* DB was written in this txn */
  #define DBI_STALE MDBX_DBI_STALE /* Named-DB record is older than txnID */
  #define DBI_FRESH MDBX_DBI_FRESH /* Named-DB handle opened in this txn */
  #define DBI_CREAT MDBX_DBI_CREAT /* Named-DB handle created in this txn */
  #define DBI_VALID 0x10           /* DB handle is valid, see also DB_VALID */
  #define DBI_USRVALID 0x20        /* As DB_VALID, but not set for FREE_DBI */
  #define DBI_DUPDATA 0x40         /* DB is MDBX_DUPSORT data */
  #define DBI_AUDITED 0x80         /* Internal flag for accounting during audit */
    /* Array of flags for each DB */
    uint8_t *mt_dbistate;
    /* Number of DB records in use, or 0 when the txn is finished.
     * This number only ever increments until the txn finishes; we
     * don't decrement it when individual DB handles are closed. */
    MDBX_dbi mt_numdbs;
    size_t mt_owner; /* thread ID that owns this transaction */
    MDBX_canary mt_canary;
    void *mt_userctx; /* User-settable context */
  
    union {
      struct {
        /* For read txns: This thread/txn's reader table slot, or NULL. */
        MDBX_reader *reader;
      } to;
      struct {
        /* In write txns, array of cursors for each DB */
        MDBX_cursor **cursors;
        pgno_t *reclaimed_pglist; /* Reclaimed GC pages */
        txnid_t last_reclaimed;   /* ID of last used record */
        pgno_t loose_refund_wl /* FIXME: describe */;
        /* dirtylist room: Dirty array size - dirty pages visible to this txn.
         * Includes ancestor txns' dirty pages not hidden by other txns'
         * dirty/spilled pages. Thus commit(nested txn) has room to merge
         * dirtylist into mt_parent after freeing hidden mt_parent pages. */
        unsigned dirtyroom;
        /* For write txns: Modified pages. Sorted when not MDBX_WRITEMAP. */
        MDBX_DPL dirtylist;
        /* The list of reclaimed txns from GC */
        MDBX_TXL lifo_reclaimed;
        /* The list of pages that became unused during this transaction. */
        MDBX_PNL retired_pages;
        /* The list of loose pages that became unused and may be reused
         * in this transaction, linked through `mp_next`. */
        MDBX_page *loose_pages;
        /* Number of loose pages (tw.loose_pages) */
        unsigned loose_count;
        /* Number of retired to parent pages (tw.retired2parent_pages) */
        unsigned retired2parent_count;
        /* The list of parent's txn dirty pages that retired (became unused)
         * in this transaction, linked through `mp_next`. */
        MDBX_page *retired2parent_pages;
        /* The sorted list of dirty pages we temporarily wrote to disk
         * because the dirty list was full. page numbers in here are
         * shifted left by 1, deleted slots have the LSB set. */
        MDBX_PNL spill_pages;
      } tw;
    };
  };
  
  /* Enough space for 2^32 nodes with minimum of 2 keys per node. I.e., plenty.
   * At 4 keys per node, enough for 2^64 nodes, so there's probably no need to
   * raise this on a 64 bit machine. */
  #if MDBX_WORDBITS >= 64
  #define CURSOR_STACK 28
  #else
  #define CURSOR_STACK 20
  #endif
  
  struct MDBX_xcursor;
  
  /* Cursors are used for all DB operations.
   * A cursor holds a path of (page pointer, key index) from the DB
   * root to a position in the DB, plus other state. MDBX_DUPSORT
   * cursors include an xcursor to the current data item. Write txns
   * track their cursors and keep them up to date when data moves.
   * Exception: An xcursor's pointer to a P_SUBP page can be stale.
   * (A node with F_DUPDATA but no F_SUBDATA contains a subpage). */
  struct MDBX_cursor {
  #define MDBX_MC_LIVE UINT32_C(0xFE05D5B1)
  #define MDBX_MC_READY4CLOSE UINT32_C(0x2817A047)
  #define MDBX_MC_WAIT4EOT UINT32_C(0x90E297A7)
    uint32_t mc_signature;
    /* The database handle this cursor operates on */
    MDBX_dbi mc_dbi;
    /* Next cursor on this DB in this txn */
    MDBX_cursor *mc_next;
    /* Backup of the original cursor if this cursor is a shadow */
    MDBX_cursor *mc_backup;
    /* Context used for databases with MDBX_DUPSORT, otherwise NULL */
    struct MDBX_xcursor *mc_xcursor;
    /* The transaction that owns this cursor */
    MDBX_txn *mc_txn;
    /* The database record for this cursor */
    MDBX_db *mc_db;
    /* The database auxiliary record for this cursor */
    MDBX_dbx *mc_dbx;
    /* The mt_dbistate for this database */
    uint8_t *mc_dbistate;
    unsigned mc_snum; /* number of pushed pages */
    unsigned mc_top;  /* index of top page, normally mc_snum-1 */
  
    /* Cursor state flags. */
  #define C_INITIALIZED 0x01 /* cursor has been initialized and is valid */
  #define C_EOF 0x02         /* No more data */
  #define C_SUB 0x04         /* Cursor is a sub-cursor */
  #define C_DEL 0x08         /* last op was a cursor_del */
  #define C_UNTRACK 0x10     /* Un-track cursor when closing */
  #define C_RECLAIMING 0x20  /* GC lookup is prohibited */
  #define C_GCFREEZE 0x40    /* reclaimed_pglist must not be updated */
  
    /* Cursor checking flags. */
  #define C_COPYING 0x100  /* skip key-value length check (copying simplify) */
  #define C_UPDATING 0x200 /* update/rebalance pending */
  #define C_RETIRING 0x400 /* refs to child pages may be invalid */
  #define C_SKIPORD 0x800  /* don't check keys ordering */
  
    unsigned mc_flags;              /* see mdbx_cursor */
    MDBX_page *mc_pg[CURSOR_STACK]; /* stack of pushed pages */
    indx_t mc_ki[CURSOR_STACK];     /* stack of page indices */
  };
  
  /* Context for sorted-dup records.
   * We could have gone to a fully recursive design, with arbitrarily
   * deep nesting of sub-databases. But for now we only handle these
   * levels - main DB, optional sub-DB, sorted-duplicate DB. */
  typedef struct MDBX_xcursor {
    /* A sub-cursor for traversing the Dup DB */
    MDBX_cursor mx_cursor;
    /* The database record for this Dup DB */
    MDBX_db mx_db;
    /* The auxiliary DB record for this Dup DB */
    MDBX_dbx mx_dbx;
    /* The mt_dbistate for this Dup DB */
    uint8_t mx_dbistate;
  } MDBX_xcursor;
  
  typedef struct MDBX_cursor_couple {
    MDBX_cursor outer;
    void *mc_userctx; /* User-settable context */
    MDBX_xcursor inner;
  } MDBX_cursor_couple;
  
  /* The database environment. */
  struct MDBX_env {
  #define MDBX_ME_SIGNATURE UINT32_C(0x9A899641)
    uint32_t me_signature;
    /* Failed to update the meta page. Probably an I/O error. */
  #define MDBX_FATAL_ERROR UINT32_C(0x80000000)
    /* Some fields are initialized. */
  #define MDBX_ENV_ACTIVE UINT32_C(0x20000000)
    /* me_txkey is set */
  #define MDBX_ENV_TXKEY UINT32_C(0x10000000)
    /* Legacy MDBX_MAPASYNC (prior v0.9) */
  #define MDBX_DEPRECATED_MAPASYNC UINT32_C(0x100000)
  #define ENV_INTERNAL_FLAGS (MDBX_FATAL_ERROR | MDBX_ENV_ACTIVE | MDBX_ENV_TXKEY)
    uint32_t me_flags;
    mdbx_mmap_t me_dxb_mmap; /* The main data file */
  #define me_map me_dxb_mmap.dxb
  #define me_lazy_fd me_dxb_mmap.fd
    mdbx_filehandle_t me_dsync_fd;
    mdbx_mmap_t me_lck_mmap; /* The lock file */
  #define me_lfd me_lck_mmap.fd
  #define me_lck me_lck_mmap.lck
  
    unsigned me_psize;    /* DB page size, initialized from me_os_psize */
    uint8_t me_psize2log; /* log2 of DB page size */
    int8_t me_stuck_meta; /* recovery-only: target meta page or less that zero */
    unsigned me_os_psize; /* OS page size, from mdbx_syspagesize() */
    unsigned me_maxreaders; /* size of the reader table */
    mdbx_fastmutex_t me_dbi_lock;
    MDBX_dbi me_numdbs;         /* number of DBs opened */
    MDBX_dbi me_maxdbs;         /* size of the DB table */
    uint32_t me_pid;            /* process ID of this env */
    mdbx_thread_key_t me_txkey; /* thread-key for readers */
    char *me_pathname;          /* path to the DB files */
    void *me_pbuf;              /* scratch area for DUPSORT put() */
    MDBX_txn *me_txn;           /* current write transaction */
    MDBX_txn *me_txn0;          /* prealloc'd write transaction */
  
    /* write-txn lock */
  #if MDBX_LOCKING == MDBX_LOCKING_SYSV
    union {
      key_t key;
      int semid;
    } me_sysv_ipc;
  #endif /* MDBX_LOCKING == MDBX_LOCKING_SYSV */
  
  #if MDBX_LOCKING > 0
    mdbx_ipclock_t *me_wlock;
  #endif /* MDBX_LOCKING > 0 */
  
    MDBX_dbx *me_dbxs;           /* array of static DB info */
    uint16_t *me_dbflags;        /* array of flags from MDBX_db.md_flags */
    unsigned *me_dbiseqs;        /* array of dbi sequence numbers */
    volatile txnid_t *me_oldest; /* ID of oldest reader last time we looked */
    MDBX_page *me_dpages;        /* list of malloc'd blocks for re-use */
    /* PNL of pages that became unused in a write txn */
    MDBX_PNL me_retired_pages;
    /* MDBX_DP of pages written during a write txn. */
    MDBX_DPL me_dirtylist;
    /* Number of freelist items that can fit in a single overflow page */
    unsigned me_maxgc_ov1page;
    unsigned me_branch_nodemax; /* max size of a branch-node */
    uint32_t me_live_reader;    /* have liveness lock in reader table */
    void *me_userctx;           /* User-settable context */
    volatile uint64_t *me_sync_timestamp;
    volatile uint64_t *me_autosync_period;
    volatile pgno_t *me_unsynced_pages;
    volatile pgno_t *me_autosync_threshold;
    volatile pgno_t *me_discarded_tail;
    volatile uint32_t *me_meta_sync_txnid;
    MDBX_hsr_func *me_hsr_callback; /* Callback for kicking laggard readers */
    struct {
  #if MDBX_LOCKING > 0
      mdbx_ipclock_t wlock;
  #endif /* MDBX_LOCKING > 0 */
      txnid_t oldest;
      uint64_t sync_timestamp;
      uint64_t autosync_period;
      pgno_t autosync_pending;
      pgno_t autosync_threshold;
      pgno_t discarded_tail;
      uint32_t meta_sync_txnid;
    } me_lckless_stub;
  #if MDBX_DEBUG
    MDBX_assert_func *me_assert_func; /*  Callback for assertion failures */
  #endif
  #ifdef MDBX_USE_VALGRIND
    int me_valgrind_handle;
  #endif
  #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
    pgno_t me_poison_edge;
  #endif /* MDBX_USE_VALGRIND || __SANITIZE_ADDRESS__ */
    MDBX_env *me_lcklist_next;
  
    /* struct me_dbgeo used for accepting db-geo params from user for the new
     * database creation, i.e. when mdbx_env_set_geometry() was called before
     * mdbx_env_open(). */
    struct {
      size_t lower;  /* minimal size of datafile */
      size_t upper;  /* maximal size of datafile */
      size_t now;    /* current size of datafile */
      size_t grow;   /* step to grow datafile */
      size_t shrink; /* threshold to shrink datafile */
    } me_dbgeo;
  
  #if defined(_WIN32) || defined(_WIN64)
    MDBX_srwlock me_remap_guard;
    /* Workaround for LockFileEx and WriteFile multithread bug */
    CRITICAL_SECTION me_windowsbug_lock;
  #else
    mdbx_fastmutex_t me_remap_guard;
  #endif
  };
  
  #ifndef __cplusplus
  /*----------------------------------------------------------------------------*/
  /* Debug and Logging stuff */
  
  #define MDBX_RUNTIME_FLAGS_INIT                                                \
    ((MDBX_DEBUG) > 0) * MDBX_DBG_ASSERT + ((MDBX_DEBUG) > 1) * MDBX_DBG_AUDIT
  
  extern uint8_t mdbx_runtime_flags;
  extern uint8_t mdbx_loglevel;
  extern MDBX_debug_func *mdbx_debug_logger;
  
  MDBX_INTERNAL_FUNC void MDBX_PRINTF_ARGS(4, 5)
      mdbx_debug_log(int level, const char *function, int line, const char *fmt,
                     ...) MDBX_PRINTF_ARGS(4, 5);
  MDBX_INTERNAL_FUNC void mdbx_debug_log_va(int level, const char *function,
                                            int line, const char *fmt,
                                            va_list args);
  
  #define mdbx_log_enabled(msg) unlikely(msg <= mdbx_loglevel)
  
  #if MDBX_DEBUG
  
  #define mdbx_assert_enabled() unlikely(mdbx_runtime_flags &MDBX_DBG_ASSERT)
  
  #define mdbx_audit_enabled() unlikely(mdbx_runtime_flags &MDBX_DBG_AUDIT)
  
  #else /* MDBX_DEBUG */
  
  #define mdbx_audit_enabled() (0)
  
  #if !defined(NDEBUG) || defined(MDBX_FORCE_ASSERTIONS)
  #define mdbx_assert_enabled() (1)
  #else
  #define mdbx_assert_enabled() (0)
  #endif /* NDEBUG */
  
  #endif /* MDBX_DEBUG */
  
  #if !MDBX_DEBUG && defined(__ANDROID_API__)
  #define mdbx_assert_fail(env, msg, func, line)                                 \
    __android_log_assert(msg, "mdbx", "%s:%u", func, line)
  #else
  void mdbx_assert_fail(const MDBX_env *env, const char *msg, const char *func,
                        int line);
  #endif
  
  #define mdbx_debug_extra(fmt, ...)                                             \
    do {                                                                         \
      if (MDBX_DEBUG && mdbx_log_enabled(MDBX_LOG_EXTRA))                        \
        mdbx_debug_log(MDBX_LOG_EXTRA, __func__, __LINE__, fmt, __VA_ARGS__);    \
    } while (0)
  
  #define mdbx_debug_extra_print(fmt, ...)                                       \
    do {                                                                         \
      if (MDBX_DEBUG && mdbx_log_enabled(MDBX_LOG_EXTRA))                        \
        mdbx_debug_log(MDBX_LOG_EXTRA, NULL, 0, fmt, __VA_ARGS__);               \
    } while (0)
  
  #define mdbx_trace(fmt, ...)                                                   \
    do {                                                                         \
      if (MDBX_DEBUG && mdbx_log_enabled(MDBX_LOG_TRACE))                        \
        mdbx_debug_log(MDBX_LOG_TRACE, __func__, __LINE__, fmt "\n",             \
                       __VA_ARGS__);                                             \
    } while (0)
  
  #define mdbx_debug(fmt, ...)                                                   \
    do {                                                                         \
      if (MDBX_DEBUG && mdbx_log_enabled(MDBX_LOG_DEBUG))                        \
        mdbx_debug_log(MDBX_LOG_DEBUG, __func__, __LINE__, fmt "\n",             \
                       __VA_ARGS__);                                             \
    } while (0)
  
  #define mdbx_verbose(fmt, ...)                                                 \
    do {                                                                         \
      if (MDBX_DEBUG && mdbx_log_enabled(MDBX_LOG_VERBOSE))                      \
        mdbx_debug_log(MDBX_LOG_VERBOSE, __func__, __LINE__, fmt "\n",           \
                       __VA_ARGS__);                                             \
    } while (0)
  
  #define mdbx_notice(fmt, ...)                                                  \
    do {                                                                         \
      if (mdbx_log_enabled(MDBX_LOG_NOTICE))                                     \
        mdbx_debug_log(MDBX_LOG_NOTICE, __func__, __LINE__, fmt "\n",            \
                       __VA_ARGS__);                                             \
    } while (0)
  
  #define mdbx_warning(fmt, ...)                                                 \
    do {                                                                         \
      if (mdbx_log_enabled(MDBX_LOG_WARN))                                       \
        mdbx_debug_log(MDBX_LOG_WARN, __func__, __LINE__, fmt "\n",              \
                       __VA_ARGS__);                                             \
    } while (0)
  
  #define mdbx_error(fmt, ...)                                                   \
    do {                                                                         \
      if (mdbx_log_enabled(MDBX_LOG_ERROR))                                      \
        mdbx_debug_log(MDBX_LOG_ERROR, __func__, __LINE__, fmt "\n",             \
                       __VA_ARGS__);                                             \
    } while (0)
  
  #define mdbx_fatal(fmt, ...)                                                   \
    mdbx_debug_log(MDBX_LOG_FATAL, __func__, __LINE__, fmt "\n", __VA_ARGS__);
  
  #define mdbx_ensure_msg(env, expr, msg)                                        \
    do {                                                                         \
      if (unlikely(!(expr)))                                                     \
        mdbx_assert_fail(env, msg, __func__, __LINE__);                          \
    } while (0)
  
  #define mdbx_ensure(env, expr) mdbx_ensure_msg(env, expr, #expr)
  
  /* assert(3) variant in environment context */
  #define mdbx_assert(env, expr)                                                 \
    do {                                                                         \
      if (mdbx_assert_enabled())                                                 \
        mdbx_ensure(env, expr);                                                  \
    } while (0)
  
  /* assert(3) variant in cursor context */
  #define mdbx_cassert(mc, expr) mdbx_assert((mc)->mc_txn->mt_env, expr)
  
  /* assert(3) variant in transaction context */
  #define mdbx_tassert(txn, expr) mdbx_assert((txn)->mt_env, expr)
  
  #ifndef MDBX_TOOLS /* Avoid using internal mdbx_assert() */
  #undef assert
  #define assert(expr) mdbx_assert(NULL, expr)
  #endif
  
  /*----------------------------------------------------------------------------*/
  /* Cache coherence and mmap invalidation */
  
  #if MDBX_CPU_WRITEBACK_INCOHERENT
  #define mdbx_flush_incoherent_cpu_writeback() mdbx_memory_barrier()
  #else
  #define mdbx_flush_incoherent_cpu_writeback() mdbx_compiler_barrier()
  #endif /* MDBX_CPU_WRITEBACK_INCOHERENT */
  
  static __maybe_unused __inline void
  mdbx_flush_incoherent_mmap(void *addr, size_t nbytes, const intptr_t pagesize) {
  #if MDBX_MMAP_INCOHERENT_FILE_WRITE
    char *const begin = (char *)(-pagesize & (intptr_t)addr);
    char *const end =
        (char *)(-pagesize & (intptr_t)((char *)addr + nbytes + pagesize - 1));
    int err = msync(begin, end - begin, MS_SYNC | MS_INVALIDATE) ? errno : 0;
    mdbx_assert(nullptr, err == 0);
    (void)err;
  #else
    (void)pagesize;
  #endif /* MDBX_MMAP_INCOHERENT_FILE_WRITE */
  
  #if MDBX_MMAP_INCOHERENT_CPU_CACHE
  #ifdef DCACHE
    /* MIPS has cache coherency issues.
     * Note: for any nbytes >= on-chip cache size, entire is flushed. */
    cacheflush(addr, nbytes, DCACHE);
  #else
  #error "Oops, cacheflush() not available"
  #endif /* DCACHE */
  #endif /* MDBX_MMAP_INCOHERENT_CPU_CACHE */
  
  #if !MDBX_MMAP_INCOHERENT_FILE_WRITE && !MDBX_MMAP_INCOHERENT_CPU_CACHE
    (void)addr;
    (void)nbytes;
  #endif
  }
  
  /*----------------------------------------------------------------------------*/
  /* Internal prototypes */
  
  MDBX_INTERNAL_FUNC int mdbx_cleanup_dead_readers(MDBX_env *env, int rlocked,
                                                   int *dead);
  MDBX_INTERNAL_FUNC int mdbx_rthc_alloc(mdbx_thread_key_t *key,
                                         MDBX_reader *begin, MDBX_reader *end);
  MDBX_INTERNAL_FUNC void mdbx_rthc_remove(const mdbx_thread_key_t key);
  
  MDBX_INTERNAL_FUNC void mdbx_rthc_global_init(void);
  MDBX_INTERNAL_FUNC void mdbx_rthc_global_dtor(void);
  MDBX_INTERNAL_FUNC void mdbx_rthc_thread_dtor(void *ptr);
  
  static __maybe_unused __inline void mdbx_jitter4testing(bool tiny) {
  #if MDBX_DEBUG
    if (MDBX_DBG_JITTER & mdbx_runtime_flags)
      mdbx_osal_jitter(tiny);
  #else
    (void)tiny;
  #endif
  }
  
  #endif /* !__cplusplus */
  
  #define MDBX_IS_ERROR(rc)                                                      \
    ((rc) != MDBX_RESULT_TRUE && (rc) != MDBX_RESULT_FALSE)
  
  /* Internal error codes, not exposed outside libmdbx */
  #define MDBX_NO_ROOT (MDBX_LAST_ADDED_ERRCODE + 10)
  
  /* Debugging output value of a cursor DBI: Negative in a sub-cursor. */
  #define DDBI(mc)                                                               \
    (((mc)->mc_flags & C_SUB) ? -(int)(mc)->mc_dbi : (int)(mc)->mc_dbi)
  
  /* Key size which fits in a DKBUF. */
  #define DKBUF_MAXKEYSIZE 511 /* FIXME */
  
  #if MDBX_DEBUG
  #define DKBUF char _kbuf[DKBUF_MAXKEYSIZE * 4 + 2]
  #define DKEY(x) mdbx_dump_val(x, _kbuf, DKBUF_MAXKEYSIZE * 2 + 1)
  #define DVAL(x)                                                                \
    mdbx_dump_val(x, _kbuf + DKBUF_MAXKEYSIZE * 2 + 1, DKBUF_MAXKEYSIZE * 2 + 1)
  #else
  #define DKBUF ((void)(0))
  #define DKEY(x) ("-")
  #define DVAL(x) ("-")
  #endif
  
  /* An invalid page number.
   * Mainly used to denote an empty tree. */
  #define P_INVALID (~(pgno_t)0)
  
  /* Test if the flags f are set in a flag word w. */
  #define F_ISSET(w, f) (((w) & (f)) == (f))
  
  /* Round n up to an even number. */
  #define EVEN(n) (((n) + 1U) & -2) /* sign-extending -2 to match n+1U */
  
  /* Default size of memory map.
   * This is certainly too small for any actual applications. Apps should
   * always set  the size explicitly using mdbx_env_set_mapsize(). */
  #define DEFAULT_MAPSIZE MEGABYTE
  
  /* Number of slots in the reader table.
   * This value was chosen somewhat arbitrarily. The 61 is a prime number,
   * and such readers plus a couple mutexes fit into single 4KB page.
   * Applications should set the table size using mdbx_env_set_maxreaders(). */
  #define DEFAULT_READERS 61
  
  /* Test if a page is a leaf page */
  #define IS_LEAF(p) (((p)->mp_flags & P_LEAF) != 0)
  /* Test if a page is a LEAF2 page */
  #define IS_LEAF2(p) unlikely(((p)->mp_flags & P_LEAF2) != 0)
  /* Test if a page is a branch page */
  #define IS_BRANCH(p) (((p)->mp_flags & P_BRANCH) != 0)
  /* Test if a page is an overflow page */
  #define IS_OVERFLOW(p) unlikely(((p)->mp_flags & P_OVERFLOW) != 0)
  /* Test if a page is a sub page */
  #define IS_SUBP(p) (((p)->mp_flags & P_SUBP) != 0)
  /* Test if a page is dirty */
  #define IS_DIRTY(p) (((p)->mp_flags & P_DIRTY) != 0)
  
  #define PAGETYPE(p) ((p)->mp_flags & (P_BRANCH | P_LEAF | P_LEAF2 | P_OVERFLOW))
  
  /* Header for a single key/data pair within a page.
   * Used in pages of type P_BRANCH and P_LEAF without P_LEAF2.
   * We guarantee 2-byte alignment for 'MDBX_node's.
   *
   * Leaf node flags describe node contents.  F_BIGDATA says the node's
   * data part is the page number of an overflow page with actual data.
   * F_DUPDATA and F_SUBDATA can be combined giving duplicate data in
   * a sub-page/sub-database, and named databases (just F_SUBDATA). */
  typedef struct MDBX_node {
  #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
    union {
      uint32_t mn_dsize;
      uint32_t mn_pgno32;
    };
    uint8_t mn_flags; /* see mdbx_node flags */
    uint8_t mn_extra;
    uint16_t mn_ksize; /* key size */
  #else
    uint16_t mn_ksize; /* key size */
    uint8_t mn_extra;
    uint8_t mn_flags; /* see mdbx_node flags */
    union {
      uint32_t mn_pgno32;
      uint32_t mn_dsize;
    };
  #endif /* __BYTE_ORDER__ */
  
    /* mdbx_node Flags */
  #define F_BIGDATA 0x01 /* data put on overflow page */
  #define F_SUBDATA 0x02 /* data is a sub-database */
  #define F_DUPDATA 0x04 /* data has duplicates */
  
    /* valid flags for mdbx_node_add() */
  #define NODE_ADD_FLAGS (F_DUPDATA | F_SUBDATA | MDBX_RESERVE | MDBX_APPEND)
  
  #if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
      (!defined(__cplusplus) && defined(_MSC_VER))
    uint8_t mn_data[] /* key and data are appended here */;
  #endif /* C99 */
  } MDBX_node;
  
  #define DB_PERSISTENT_FLAGS                                                    \
    (MDBX_REVERSEKEY | MDBX_DUPSORT | MDBX_INTEGERKEY | MDBX_DUPFIXED |          \
     MDBX_INTEGERDUP | MDBX_REVERSEDUP)
  
  /* mdbx_dbi_open() flags */
  #define DB_USABLE_FLAGS (DB_PERSISTENT_FLAGS | MDBX_CREATE | MDBX_DB_ACCEDE)
  
  #define DB_VALID 0x8000 /* DB handle is valid, for me_dbflags */
  #define DB_INTERNAL_FLAGS DB_VALID
  
  #if DB_INTERNAL_FLAGS & DB_USABLE_FLAGS
  #error "Oops, some flags overlapped or wrong"
  #endif
  #if DB_PERSISTENT_FLAGS & ~DB_USABLE_FLAGS
  #error "Oops, some flags overlapped or wrong"
  #endif
  
  /* max number of pages to commit in one writev() call */
  #define MDBX_COMMIT_PAGES 64
  #if defined(IOV_MAX) && IOV_MAX < MDBX_COMMIT_PAGES /* sysconf(_SC_IOV_MAX) */
  #undef MDBX_COMMIT_PAGES
  #define MDBX_COMMIT_PAGES IOV_MAX
  #endif
  
  /*
   *                /
   *                | -1, a < b
   * CMP2INT(a,b) = <  0, a == b
   *                |  1, a > b
   *                \
   */
  #if 1
  /* LY: fast enough on most systems */
  #define CMP2INT(a, b) (((b) > (a)) ? -1 : (a) > (b))
  #else
  #define CMP2INT(a, b) (((a) > (b)) - ((b) > (a)))
  #endif
  
  /* Do not spill pages to disk if txn is getting full, may fail instead */
  #define MDBX_NOSPILL 0x8000
  
  MDBX_NOTHROW_CONST_FUNCTION static __maybe_unused __inline pgno_t
  pgno_add(pgno_t base, pgno_t augend) {
    assert(base <= MAX_PAGENO);
    return (augend < MAX_PAGENO - base) ? base + augend : MAX_PAGENO;
  }
  
  MDBX_NOTHROW_CONST_FUNCTION static __maybe_unused __inline pgno_t
  pgno_sub(pgno_t base, pgno_t subtrahend) {
    assert(base >= MIN_PAGENO);
    return (subtrahend < base - MIN_PAGENO) ? base - subtrahend : MIN_PAGENO;
  }
  
  MDBX_NOTHROW_CONST_FUNCTION static __always_inline __maybe_unused bool
  is_powerof2(size_t x) {
    return (x & (x - 1)) == 0;
  }
  
  MDBX_NOTHROW_CONST_FUNCTION static __always_inline __maybe_unused size_t
  floor_powerof2(size_t value, size_t granularity) {
    assert(is_powerof2(granularity));
    return value & ~(granularity - 1);
  }
  
  MDBX_NOTHROW_CONST_FUNCTION static __always_inline __maybe_unused size_t
  ceil_powerof2(size_t value, size_t granularity) {
    return floor_powerof2(value + granularity - 1, granularity);
  }
  
  /* Only a subset of the mdbx_env flags can be changed
   * at runtime. Changing other flags requires closing the
   * environment and re-opening it with the new flags. */
  #define ENV_CHANGEABLE_FLAGS                                                   \
    (MDBX_SAFE_NOSYNC | MDBX_NOMETASYNC | MDBX_DEPRECATED_MAPASYNC |             \
     MDBX_NOMEMINIT | MDBX_COALESCE | MDBX_PAGEPERTURB | MDBX_ACCEDE)
  #define ENV_CHANGELESS_FLAGS                                                   \
    (MDBX_NOSUBDIR | MDBX_RDONLY | MDBX_WRITEMAP | MDBX_NOTLS | MDBX_NORDAHEAD | \
     MDBX_LIFORECLAIM | MDBX_EXCLUSIVE)
  #define ENV_USABLE_FLAGS (ENV_CHANGEABLE_FLAGS | ENV_CHANGELESS_FLAGS)
  
  #if !defined(__cplusplus) || defined(__cpp_constexpr)
  static __maybe_unused void static_checks(void) {
    STATIC_ASSERT_MSG(INT16_MAX - CORE_DBS == MDBX_MAX_DBI,
                      "Oops, MDBX_MAX_DBI or CORE_DBS?");
    STATIC_ASSERT_MSG((unsigned)(MDBX_DB_ACCEDE | MDBX_CREATE) ==
                          ((DB_USABLE_FLAGS | DB_INTERNAL_FLAGS) &
                           (ENV_USABLE_FLAGS | ENV_INTERNAL_FLAGS)),
                      "Oops, some flags overlapped or wrong");
    STATIC_ASSERT_MSG((ENV_INTERNAL_FLAGS & ENV_USABLE_FLAGS) == 0,
                      "Oops, some flags overlapped or wrong");
  }
  #endif /* Disabled for MSVC 19.0 (VisualStudio 2015) */
  
  #ifdef __cplusplus
  }
  #endif
  /*
   * Copyright 2015-2020 Leonid Yuriev <leo@yuriev.ru>.
   * and other libmdbx authors: please see AUTHORS file.
   * All rights reserved.
   *
   * This code is derived from "LMDB engine" written by
   * Howard Chu (Symas Corporation), which itself derived from btree.c
   * written by Martin Hedenfalk.
   *
   * ---
   *
   * Portions Copyright 2011-2015 Howard Chu, Symas Corp. All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted only as authorized by the OpenLDAP
   * Public License.
   *
   * A copy of this license is available in the file LICENSE in the
   * top-level directory of the distribution or, alternatively, at
   * <http://www.OpenLDAP.org/license.html>.
   *
   * ---
   *
   * Portions Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
   *
   * Permission to use, copy, modify, and distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
   * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
  
  
  /*------------------------------------------------------------------------------
   * Internal inline functions */
  
  MDBX_NOTHROW_CONST_FUNCTION static unsigned log2n(size_t value) {
    assert(value > 0 && value < INT32_MAX && is_powerof2(value));
    assert((value & -(int32_t)value) == value);
  #if __GNUC_PREREQ(4, 1) || __has_builtin(__builtin_ctzl)
    return __builtin_ctzl(value);
  #elif defined(_MSC_VER)
    unsigned long index;
    _BitScanForward(&index, (unsigned long)value);
    return index;
  #else
    static const uint8_t debruijn_ctz32[32] = {
        0,  1,  28, 2,  29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4,  8,
        31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6,  11, 5,  10, 9};
    return debruijn_ctz32[(uint32_t)(value * 0x077CB531u) >> 27];
  #endif
  }
  
  /*------------------------------------------------------------------------------
   * Unaligned access */
  
  MDBX_NOTHROW_CONST_FUNCTION static __maybe_unused __always_inline unsigned
  field_alignment(unsigned alignment_baseline, size_t field_offset) {
    unsigned merge = alignment_baseline | (unsigned)field_offset;
    return merge & -(int)merge;
  }
  
  /* read-thunk for UB-sanitizer */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline uint8_t
  peek_u8(const uint8_t *const __restrict ptr) {
    return *ptr;
  }
  
  /* write-thunk for UB-sanitizer */
  static __always_inline void poke_u8(uint8_t *const __restrict ptr,
                                      const uint8_t v) {
    *ptr = v;
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline uint16_t
  unaligned_peek_u16(const unsigned expected_alignment, const void *const ptr) {
    assert((uintptr_t)ptr % expected_alignment == 0);
    if (MDBX_UNALIGNED_OK || (expected_alignment % sizeof(uint16_t)) == 0)
      return *(const uint16_t *)ptr;
    else {
      uint16_t v;
      memcpy(&v, ptr, sizeof(v));
      return v;
    }
  }
  
  static __always_inline void
  unaligned_poke_u16(const unsigned expected_alignment,
                     void *const __restrict ptr, const uint16_t v) {
    assert((uintptr_t)ptr % expected_alignment == 0);
    if (MDBX_UNALIGNED_OK || (expected_alignment % sizeof(v)) == 0)
      *(uint16_t *)ptr = v;
    else
      memcpy(ptr, &v, sizeof(v));
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline uint32_t unaligned_peek_u32(
      const unsigned expected_alignment, const void *const __restrict ptr) {
    assert((uintptr_t)ptr % expected_alignment == 0);
    if (MDBX_UNALIGNED_OK || (expected_alignment % sizeof(uint32_t)) == 0)
      return *(const uint32_t *)ptr;
    else if ((expected_alignment % sizeof(uint16_t)) == 0) {
      const uint16_t lo =
          ((const uint16_t *)ptr)[__BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__];
      const uint16_t hi =
          ((const uint16_t *)ptr)[__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__];
      return lo | (uint32_t)hi << 16;
    } else {
      uint32_t v;
      memcpy(&v, ptr, sizeof(v));
      return v;
    }
  }
  
  static __always_inline void
  unaligned_poke_u32(const unsigned expected_alignment,
                     void *const __restrict ptr, const uint32_t v) {
    assert((uintptr_t)ptr % expected_alignment == 0);
    if (MDBX_UNALIGNED_OK || (expected_alignment % sizeof(v)) == 0)
      *(uint32_t *)ptr = v;
    else if ((expected_alignment % sizeof(uint16_t)) == 0) {
      ((uint16_t *)ptr)[__BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__] = (uint16_t)v;
      ((uint16_t *)ptr)[__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__] =
          (uint16_t)(v >> 16);
    } else
      memcpy(ptr, &v, sizeof(v));
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline uint64_t unaligned_peek_u64(
      const unsigned expected_alignment, const void *const __restrict ptr) {
    assert((uintptr_t)ptr % expected_alignment == 0);
    if (MDBX_UNALIGNED_OK || (expected_alignment % sizeof(uint64_t)) == 0)
      return *(const uint64_t *)ptr;
    else if ((expected_alignment % sizeof(uint32_t)) == 0) {
      const uint32_t lo =
          ((const uint32_t *)ptr)[__BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__];
      const uint32_t hi =
          ((const uint32_t *)ptr)[__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__];
      return lo | (uint64_t)hi << 32;
    } else {
      uint64_t v;
      memcpy(&v, ptr, sizeof(v));
      return v;
    }
  }
  
  static __always_inline void
  unaligned_poke_u64(const unsigned expected_alignment,
                     void *const __restrict ptr, const uint64_t v) {
    assert((uintptr_t)ptr % expected_alignment == 0);
    if (MDBX_UNALIGNED_OK || (expected_alignment % sizeof(v)) == 0)
      *(uint64_t *)ptr = v;
    else if ((expected_alignment % sizeof(uint32_t)) == 0) {
      ((uint32_t *)ptr)[__BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__] = (uint32_t)v;
      ((uint32_t *)ptr)[__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__] =
          (uint32_t)(v >> 32);
    } else
      memcpy(ptr, &v, sizeof(v));
  }
  
  #define UNALIGNED_PEEK_8(ptr, struct, field)                                   \
    peek_u8((const uint8_t *)(ptr) + offsetof(struct, field))
  #define UNALIGNED_POKE_8(ptr, struct, field, value)                            \
    poke_u8((uint8_t *)(ptr) + offsetof(struct, field), value)
  
  #define UNALIGNED_PEEK_16(ptr, struct, field)                                  \
    unaligned_peek_u16(1, (const char *)(ptr) + offsetof(struct, field))
  #define UNALIGNED_POKE_16(ptr, struct, field, value)                           \
    unaligned_poke_u16(1, (char *)(ptr) + offsetof(struct, field), value)
  
  #define UNALIGNED_PEEK_32(ptr, struct, field)                                  \
    unaligned_peek_u32(1, (const char *)(ptr) + offsetof(struct, field))
  #define UNALIGNED_POKE_32(ptr, struct, field, value)                           \
    unaligned_poke_u32(1, (char *)(ptr) + offsetof(struct, field), value)
  
  #define UNALIGNED_PEEK_64(ptr, struct, field)                                  \
    unaligned_peek_u64(1, (const char *)(ptr) + offsetof(struct, field))
  #define UNALIGNED_POKE_64(ptr, struct, field, value)                           \
    unaligned_poke_u64(1, (char *)(ptr) + offsetof(struct, field), value)
  
  /* Get the page number pointed to by a branch node */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline pgno_t
  node_pgno(const MDBX_node *const __restrict node) {
    pgno_t pgno = UNALIGNED_PEEK_32(node, MDBX_node, mn_pgno32);
    if (sizeof(pgno) > 4)
      pgno |= ((uint64_t)UNALIGNED_PEEK_8(node, MDBX_node, mn_extra)) << 32;
    return pgno;
  }
  
  /* Set the page number in a branch node */
  static __always_inline void node_set_pgno(MDBX_node *const __restrict node,
                                            pgno_t pgno) {
    assert(pgno >= MIN_PAGENO && pgno <= MAX_PAGENO);
  
    UNALIGNED_POKE_32(node, MDBX_node, mn_pgno32, (uint32_t)pgno);
    if (sizeof(pgno) > 4)
      UNALIGNED_POKE_8(node, MDBX_node, mn_extra,
                       (uint8_t)((uint64_t)pgno >> 32));
  }
  
  /* Get the size of the data in a leaf node */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline size_t
  node_ds(const MDBX_node *const __restrict node) {
    return UNALIGNED_PEEK_32(node, MDBX_node, mn_dsize);
  }
  
  /* Set the size of the data for a leaf node */
  static __always_inline void node_set_ds(MDBX_node *const __restrict node,
                                          size_t size) {
    assert(size < INT_MAX);
    UNALIGNED_POKE_32(node, MDBX_node, mn_dsize, (uint32_t)size);
  }
  
  /* The size of a key in a node */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline size_t
  node_ks(const MDBX_node *const __restrict node) {
    return UNALIGNED_PEEK_16(node, MDBX_node, mn_ksize);
  }
  
  /* Set the size of the key for a leaf node */
  static __always_inline void node_set_ks(MDBX_node *const __restrict node,
                                          size_t size) {
    assert(size < INT16_MAX);
    UNALIGNED_POKE_16(node, MDBX_node, mn_ksize, (uint16_t)size);
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline uint8_t
  node_flags(const MDBX_node *const __restrict node) {
    return UNALIGNED_PEEK_8(node, MDBX_node, mn_flags);
  }
  
  static __always_inline void node_set_flags(MDBX_node *const __restrict node,
                                             uint8_t flags) {
    UNALIGNED_POKE_8(node, MDBX_node, mn_flags, flags);
  }
  
  /* Size of the node header, excluding dynamic data at the end */
  #define NODESIZE offsetof(MDBX_node, mn_data)
  
  /* Address of the key for the node */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline void *
  node_key(const MDBX_node *const __restrict node) {
    return (char *)node + NODESIZE;
  }
  
  /* Address of the data for a node */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline void *
  node_data(const MDBX_node *const __restrict node) {
    return (char *)node_key(node) + node_ks(node);
  }
  
  /* Size of a node in a leaf page with a given key and data.
   * This is node header plus key plus data size. */
  MDBX_NOTHROW_CONST_FUNCTION static __always_inline size_t
  node_size_len(const size_t key_len, const size_t value_len) {
    return NODESIZE + EVEN(key_len + value_len);
  }
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline size_t
  node_size(const MDBX_val *key, const MDBX_val *value) {
    return node_size_len(key ? key->iov_len : 0, value ? value->iov_len : 0);
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline pgno_t
  peek_pgno(const void *const __restrict ptr) {
    if (sizeof(pgno_t) == sizeof(uint32_t))
      return (pgno_t)unaligned_peek_u32(1, ptr);
    else if (sizeof(pgno_t) == sizeof(uint64_t))
      return (pgno_t)unaligned_peek_u64(1, ptr);
    else {
      pgno_t pgno;
      memcpy(&pgno, ptr, sizeof(pgno));
      return pgno;
    }
  }
  
  static __always_inline void poke_pgno(void *const __restrict ptr,
                                        const pgno_t pgno) {
    if (sizeof(pgno) == sizeof(uint32_t))
      unaligned_poke_u32(1, ptr, pgno);
    else if (sizeof(pgno) == sizeof(uint64_t))
      unaligned_poke_u64(1, ptr, pgno);
    else
      memcpy(ptr, &pgno, sizeof(pgno));
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline pgno_t
  node_largedata_pgno(const MDBX_node *const __restrict node) {
    assert(node_flags(node) & F_BIGDATA);
    return peek_pgno(node_data(node));
  }
  
  /*------------------------------------------------------------------------------
   * Key length limitation factors:
   *
   *  - Branch-page must contain at least two (MDBX_MINKEYS) nodes,
   *    within each a key and a child page number. But we can't split a page if
   *    it contains less that 4 keys. Therefore, at least 3 branch-node should
   *    fit in the single branch-page:
   *      pageroom = pagesize - page_hdr_len;
   *      branch.maxnode = even_floor(pageroom / 3 - sizeof(indx_t));
   *      branch.maxkey = branch.maxnode - node_hdr_len;
   *
   *  - Leaf-node of non-dupsort database must fit into one leaf-page,
   *    where a value could be placed on a large/overflow page:
   *      leaf.maxnode = even_floor(pageroom - sizeof(indx_t));
   *      leaf.maxkey = leaf.maxnode - node_hdr_len - sizeof(pgno_t);
   *
   *  - SubDatabase-node must fit into one leaf-page:
   *      subdb.maxname = leaf.maxnode - node_hdr_len - sizeof(MDBX_db);
   *
   *  - Dupsort values itself are a keys in a dupsort-subdb and couldn't be
   *    longer than the branch.maxkey. But dupsort node must fit into one
   *    leaf-page, since dupsort value couldn't be placed on a large/overflow
   *    page.
   *
   * - So, the simplest solution is to use half of branch.maxkey as
   *   a common maxkey value. Nevertheless, the actual values of maxkey are:
   *     nondupsort.maxkey = even_floor(pageroom / 3)
   *                           - sizeof(indx_t) - node_hdr_len;
   *     dupsort.maxkey(value) = min(nondupsort.maxkey,
   *                                 leaf.maxnode - even_ceil(length(value)));
   */
  
  #define PAGEROOM(pagesize) ((pagesize)-PAGEHDRSZ)
  #define EVEN_FLOOR(n) ((n) & ~(size_t)1)
  #define BRANCH_NODEMAX(pagesize)                                               \
    (EVEN_FLOOR(PAGEROOM(pagesize) / (MDBX_MINKEYS * 2 - 1)) - sizeof(indx_t))
  #define LEAF_NODEMAX(pagesize) (PAGEROOM(pagesize) - sizeof(indx_t))
  #define MAX_GC1OVPAGE(pagesize) (PAGEROOM(pagesize) / sizeof(pgno_t) - 1)
  
  __cold int mdbx_env_get_maxkeysize(const MDBX_env *env) {
    return mdbx_env_get_maxkeysize_ex(env, MDBX_DUPSORT);
  }
  
  __cold int mdbx_env_get_maxkeysize_ex(const MDBX_env *env,
                                        MDBX_db_flags_t flags) {
    if (unlikely(!env || env->me_signature != MDBX_ME_SIGNATURE))
      return -1;
  
    return (int)mdbx_limits_keysize_max((intptr_t)env->me_psize, flags);
  }
  
  __cold intptr_t mdbx_limits_keysize_max(intptr_t pagesize,
                                          MDBX_db_flags_t flags) {
    if (pagesize < 1)
      pagesize = (intptr_t)mdbx_syspagesize();
    if (unlikely(pagesize < (intptr_t)MIN_PAGESIZE ||
                 pagesize > (intptr_t)MAX_PAGESIZE ||
                 !is_powerof2((size_t)pagesize)))
      return -1;
  
    STATIC_ASSERT(BRANCH_NODEMAX(MIN_PAGESIZE) - NODESIZE - sizeof(pgno_t) >= 8);
    STATIC_ASSERT(LEAF_NODEMAX(MIN_PAGESIZE) - NODESIZE - sizeof(pgno_t) >= 8);
    STATIC_ASSERT(LEAF_NODEMAX(MIN_PAGESIZE) - NODESIZE >= sizeof(MDBX_db));
    if (flags & MDBX_INTEGERKEY)
      return 8 /* sizeof(uint64_t) */;
  
    STATIC_ASSERT(BRANCH_NODEMAX(MAX_PAGESIZE) - NODESIZE - sizeof(pgno_t) <
                  LEAF_NODEMAX(MAX_PAGESIZE) - NODESIZE - sizeof(MDBX_db));
    STATIC_ASSERT(BRANCH_NODEMAX(MIN_PAGESIZE) - NODESIZE - sizeof(pgno_t) <
                  LEAF_NODEMAX(MIN_PAGESIZE) - NODESIZE - sizeof(MDBX_db));
    if (flags &
        (MDBX_DUPSORT | MDBX_DUPFIXED | MDBX_INTEGERDUP | MDBX_REVERSEDUP))
      return BRANCH_NODEMAX(pagesize) - NODESIZE - sizeof(MDBX_db);
  
    return BRANCH_NODEMAX(pagesize) - NODESIZE - sizeof(pgno_t);
  }
  
  __cold int mdbx_env_get_maxvalsize_ex(const MDBX_env *env,
                                        MDBX_db_flags_t flags) {
    if (unlikely(!env || env->me_signature != MDBX_ME_SIGNATURE))
      return -1;
  
    return (int)mdbx_limits_valsize_max((intptr_t)env->me_psize, flags);
  }
  
  __cold intptr_t mdbx_limits_valsize_max(intptr_t pagesize,
                                          MDBX_db_flags_t flags) {
    if (pagesize < 1)
      pagesize = (intptr_t)mdbx_syspagesize();
    if (unlikely(pagesize < (intptr_t)MIN_PAGESIZE ||
                 pagesize > (intptr_t)MAX_PAGESIZE ||
                 !is_powerof2((size_t)pagesize)))
      return -1;
  
    if (flags & MDBX_INTEGERDUP)
      return 8 /* sizeof(uint64_t) */;
  
    if (flags & (MDBX_DUPSORT | MDBX_DUPFIXED | MDBX_REVERSEDUP))
      return BRANCH_NODEMAX(pagesize) - NODESIZE;
  
    const unsigned page_ln2 = log2n(pagesize);
    const size_t hard = 0x7FF00000ul;
    const size_t hard_pages = hard >> page_ln2;
    const size_t limit = (hard_pages < MDBX_DPL_TXNFULL / 3)
                             ? hard
                             : ((size_t)MDBX_DPL_TXNFULL / 3 << page_ln2);
    return (limit < MAX_MAPSIZE) ? limit / 2 : MAX_MAPSIZE / 2;
  }
  
  /* Calculate the size of a leaf node.
   *
   * The size depends on the environment's page size; if a data item
   * is too large it will be put onto an overflow page and the node
   * size will only include the key and not the data. Sizes are always
   * rounded up to an even number of bytes, to guarantee 2-byte alignment
   * of the MDBX_node headers. */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline size_t
  leaf_size(const MDBX_env *env, const MDBX_val *key, const MDBX_val *data) {
    size_t node_bytes = node_size(key, data);
    /* NOTE: The actual limit is LEAF_NODEMAX(env->me_psize), but it reasonable to
     * use env->me_branch_nodemax (which is 3 times less) as the threshold
     * because:
     *  - Large threshold implies that any insertion/update could result split
     *    a single leaf page to THREE, which requires TWO insertion into parent
     *    branch page, then could leads to split parent page and so on up to
     *    the root. Such double-splitting is complex, ie costly (in case simple
     *    clear implementation) either dangerous (in case high-optimized
     *    implementation).
     *  - This does not affect capabilities, i.e. it does not limit the maximum
     *    key size.
     *  - At a lower threshold, on average, the density of keys on leaf pages
     *    increases and the height of the tree decreases. Thus, this lead the
     *    less number of pages participating in the search, and the search
     *    speed increases.
     *  - On the other hand, there is no universal gold ratio here and with a
     *    smaller threshold, we will create more overflows/large pages,
     *    i.e. the database size will be larger as will the IOPS volume.
     *
     * So, the lower threshold is not a silver bullet, but it allow implementation
     * to be much simple and robust, without adding a flaws. */
    if (node_bytes > env->me_branch_nodemax) {
      /* put on overflow page */
      node_bytes = node_size(key, nullptr) + sizeof(pgno_t);
    }
  
    return node_bytes + sizeof(indx_t);
  }
  
  /* Calculate the size of a branch node.
   *
   * The size should depend on the environment's page size but since
   * we currently don't support spilling large keys onto overflow
   * pages, it's simply the size of the MDBX_node header plus the
   * size of the key. Sizes are always rounded up to an even number
   * of bytes, to guarantee 2-byte alignment of the MDBX_node headers.
   *
   * [in] env The environment handle.
   * [in] key The key for the node.
   *
   * Returns The number of bytes needed to store the node. */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline size_t
  branch_size(const MDBX_env *env, const MDBX_val *key) {
    /* Size of a node in a branch page with a given key.
     * This is just the node header plus the key, there is no data. */
    size_t node_bytes = node_size(key, nullptr);
    if (unlikely(node_bytes > env->me_branch_nodemax)) {
      /* put on overflow page */
      /* not implemented */
      mdbx_assert_fail(env, "INDXSIZE(key) <= env->me_nodemax", __func__,
                       __LINE__);
      node_bytes = node_size(key, nullptr) + sizeof(pgno_t);
    }
  
    return node_bytes + sizeof(indx_t);
  }
  
  MDBX_NOTHROW_CONST_FUNCTION static __always_inline uint16_t
  flags_db2sub(uint16_t db_flags) {
    uint16_t sub_flags = db_flags & MDBX_DUPFIXED;
  
    /* MDBX_INTEGERDUP => MDBX_INTEGERKEY */
  #define SHIFT_INTEGERDUP_TO_INTEGERKEY 2
    STATIC_ASSERT((MDBX_INTEGERDUP >> SHIFT_INTEGERDUP_TO_INTEGERKEY) ==
                  MDBX_INTEGERKEY);
    sub_flags |= (db_flags & MDBX_INTEGERDUP) >> SHIFT_INTEGERDUP_TO_INTEGERKEY;
  
    /* MDBX_REVERSEDUP => MDBX_REVERSEKEY */
  #define SHIFT_REVERSEDUP_TO_REVERSEKEY 5
    STATIC_ASSERT((MDBX_REVERSEDUP >> SHIFT_REVERSEDUP_TO_REVERSEKEY) ==
                  MDBX_REVERSEKEY);
    sub_flags |= (db_flags & MDBX_REVERSEDUP) >> SHIFT_REVERSEDUP_TO_REVERSEKEY;
  
    return sub_flags;
  }
  
  /*----------------------------------------------------------------------------*/
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline size_t
  pgno2bytes(const MDBX_env *env, pgno_t pgno) {
    mdbx_assert(env, (1u << env->me_psize2log) == env->me_psize);
    return ((size_t)pgno) << env->me_psize2log;
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline MDBX_page *
  pgno2page(const MDBX_env *env, pgno_t pgno) {
    return (MDBX_page *)(env->me_map + pgno2bytes(env, pgno));
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline pgno_t
  bytes2pgno(const MDBX_env *env, size_t bytes) {
    mdbx_assert(env, (env->me_psize >> env->me_psize2log) == 1);
    return (pgno_t)(bytes >> env->me_psize2log);
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static size_t
  pgno_align2os_bytes(const MDBX_env *env, pgno_t pgno) {
    return ceil_powerof2(pgno2bytes(env, pgno), env->me_os_psize);
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static pgno_t pgno_align2os_pgno(const MDBX_env *env,
                                                              pgno_t pgno) {
    return bytes2pgno(env, pgno_align2os_bytes(env, pgno));
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static size_t
  bytes_align2os_bytes(const MDBX_env *env, size_t bytes) {
    return ceil_powerof2(ceil_powerof2(bytes, env->me_psize), env->me_os_psize);
  }
  
  /* Address of first usable data byte in a page, after the header */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline void *
  page_data(const MDBX_page *mp) {
    return (char *)mp + PAGEHDRSZ;
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline const MDBX_page *
  data_page(const void *data) {
    return container_of(data, MDBX_page, mp_ptrs);
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline MDBX_meta *
  page_meta(MDBX_page *mp) {
    return (MDBX_meta *)page_data(mp);
  }
  
  /* Number of nodes on a page */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline unsigned
  page_numkeys(const MDBX_page *mp) {
    return mp->mp_lower >> 1;
  }
  
  /* The amount of space remaining in the page */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline unsigned
  page_room(const MDBX_page *mp) {
    return mp->mp_upper - mp->mp_lower;
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline unsigned
  page_space(const MDBX_env *env) {
    STATIC_ASSERT(PAGEHDRSZ % 2 == 0);
    return env->me_psize - PAGEHDRSZ;
  }
  
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline unsigned
  page_used(const MDBX_env *env, const MDBX_page *mp) {
    return page_space(env) - page_room(mp);
  }
  
  /* The percentage of space used in the page, in a percents. */
  MDBX_NOTHROW_PURE_FUNCTION static __maybe_unused __inline double
  page_fill(const MDBX_env *env, const MDBX_page *mp) {
    return page_used(env, mp) * 100.0 / page_space(env);
  }
  
  /* The number of overflow pages needed to store the given size. */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline pgno_t
  number_of_ovpages(const MDBX_env *env, size_t bytes) {
    return bytes2pgno(env, PAGEHDRSZ - 1 + bytes) + 1;
  }
  
  __cold static int MDBX_PRINTF_ARGS(2, 3)
      bad_page(const MDBX_page *mp, const char *fmt, ...) {
    if (mdbx_log_enabled(MDBX_LOG_ERROR)) {
      static const MDBX_page *prev;
      if (prev != mp) {
        prev = mp;
        mdbx_debug_log(MDBX_LOG_ERROR, "badpage", 0,
                       "corrupted page #%u, mod-txnid %" PRIaTXN " \n",
                       mp->mp_pgno, mp->mp_txnid);
      }
  
      va_list args;
      va_start(args, fmt);
      mdbx_debug_log_va(MDBX_LOG_ERROR, "badpage", 0, fmt, args);
      va_end(args);
    }
    return MDBX_CORRUPTED;
  }
  
  /* Address of node i in page p */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline MDBX_node *
  page_node(const MDBX_page *mp, unsigned i) {
    assert((mp->mp_flags & (P_LEAF2 | P_OVERFLOW | P_META)) == 0);
    assert(page_numkeys(mp) > (unsigned)(i));
    assert(mp->mp_ptrs[i] % 2 == 0);
    return (MDBX_node *)((char *)mp + mp->mp_ptrs[i] + PAGEHDRSZ);
  }
  
  /* The address of a key in a LEAF2 page.
   * LEAF2 pages are used for MDBX_DUPFIXED sorted-duplicate sub-DBs.
   * There are no node headers, keys are stored contiguously. */
  MDBX_NOTHROW_PURE_FUNCTION static __always_inline void *
  page_leaf2key(const MDBX_page *mp, unsigned i, size_t keysize) {
    assert((mp->mp_flags & (P_BRANCH | P_LEAF | P_LEAF2 | P_OVERFLOW | P_META)) ==
           (P_LEAF | P_LEAF2));
    assert(mp->mp_leaf2_ksize == keysize);
    (void)keysize;
    return (char *)mp + PAGEHDRSZ + (i * mp->mp_leaf2_ksize);
  }
  
  /* Set the node's key into keyptr. */
  static __always_inline void get_key(const MDBX_node *node, MDBX_val *keyptr) {
    keyptr->iov_len = node_ks(node);
    keyptr->iov_base = node_key(node);
  }
  
  /* Set the node's key into keyptr, if requested. */
  static __always_inline void
  get_key_optional(const MDBX_node *node, MDBX_val *keyptr /* __may_null */) {
    if (keyptr)
      get_key(node, keyptr);
  }
  
  /*------------------------------------------------------------------------------
   * Workaround for mmaped-lookahead-cross-page-boundary bug
   * in an obsolete versions of Elbrus's libc and kernels. */
  #if defined(__e2k__) && defined(MDBX_E2K_MLHCPB_WORKAROUND) &&                 \
      MDBX_E2K_MLHCPB_WORKAROUND
  int __hot mdbx_e2k_memcmp_bug_workaround(const void *s1, const void *s2,
                                           size_t n) {
    if (unlikely(n > 42
                 /* LY: align followed access if reasonable possible */
                 && (((uintptr_t)s1) & 7) != 0 &&
                 (((uintptr_t)s1) & 7) == (((uintptr_t)s2) & 7))) {
      if (((uintptr_t)s1) & 1) {
        const int diff = *(uint8_t *)s1 - *(uint8_t *)s2;
        if (diff)
          return diff;
        s1 = (char *)s1 + 1;
        s2 = (char *)s2 + 1;
        n -= 1;
      }
  
      if (((uintptr_t)s1) & 2) {
        const uint16_t a = *(uint16_t *)s1;
        const uint16_t b = *(uint16_t *)s2;
        if (likely(a != b))
          return (__builtin_bswap16(a) > __builtin_bswap16(b)) ? 1 : -1;
        s1 = (char *)s1 + 2;
        s2 = (char *)s2 + 2;
        n -= 2;
      }
  
      if (((uintptr_t)s1) & 4) {
        const uint32_t a = *(uint32_t *)s1;
        const uint32_t b = *(uint32_t *)s2;
        if (likely(a != b))
          return (__builtin_bswap32(a) > __builtin_bswap32(b)) ? 1 : -1;
        s1 = (char *)s1 + 4;
        s2 = (char *)s2 + 4;
        n -= 4;
      }
    }
  
    while (n >= 8) {
      const uint64_t a = *(uint64_t *)s1;
      const uint64_t b = *(uint64_t *)s2;
      if (likely(a != b))
        return (__builtin_bswap64(a) > __builtin_bswap64(b)) ? 1 : -1;
      s1 = (char *)s1 + 8;
      s2 = (char *)s2 + 8;
      n -= 8;
    }
  
    if (n & 4) {
      const uint32_t a = *(uint32_t *)s1;
      const uint32_t b = *(uint32_t *)s2;
      if (likely(a != b))
        return (__builtin_bswap32(a) > __builtin_bswap32(b)) ? 1 : -1;
      s1 = (char *)s1 + 4;
      s2 = (char *)s2 + 4;
    }
  
    if (n & 2) {
      const uint16_t a = *(uint16_t *)s1;
      const uint16_t b = *(uint16_t *)s2;
      if (likely(a != b))
        return (__builtin_bswap16(a) > __builtin_bswap16(b)) ? 1 : -1;
      s1 = (char *)s1 + 2;
      s2 = (char *)s2 + 2;
    }
  
    return (n & 1) ? *(uint8_t *)s1 - *(uint8_t *)s2 : 0;
  }
  
  int __hot mdbx_e2k_strcmp_bug_workaround(const char *s1, const char *s2) {
    while (true) {
      int diff = *(uint8_t *)s1 - *(uint8_t *)s2;
      if (likely(diff != 0) || *s1 == '\0')
        return diff;
      s1 += 1;
      s2 += 1;
    }
  }
  
  int __hot mdbx_e2k_strncmp_bug_workaround(const char *s1, const char *s2,
                                            size_t n) {
    while (n > 0) {
      int diff = *(uint8_t *)s1 - *(uint8_t *)s2;
      if (likely(diff != 0) || *s1 == '\0')
        return diff;
      s1 += 1;
      s2 += 1;
      n -= 1;
    }
    return 0;
  }
  
  size_t __hot mdbx_e2k_strlen_bug_workaround(const char *s) {
    size_t n = 0;
    while (*s) {
      s += 1;
      n += 1;
    }
    return n;
  }
  
  size_t __hot mdbx_e2k_strnlen_bug_workaround(const char *s, size_t maxlen) {
    size_t n = 0;
    while (maxlen > n && *s) {
      s += 1;
      n += 1;
    }
    return n;
  }
  #endif /* MDBX_E2K_MLHCPB_WORKAROUND */
  
  /*------------------------------------------------------------------------------
   * safe read/write volatile 64-bit fields on 32-bit architectures. */
  
  static __always_inline void atomic_yield(void) {
  #if defined(_WIN32) || defined(_WIN64)
    YieldProcessor();
  #elif defined(__x86_64__) || defined(__i386__) || defined(__e2k__)
    __builtin_ia32_pause();
  #elif defined(__ia64__)
  #if defined(__HP_cc__) || defined(__HP_aCC__)
    _Asm_hint(_HINT_PAUSE);
  #else
    __asm__ __volatile__("hint @pause");
  #endif
  #elif defined(__aarch64__) || (defined(__ARM_ARCH) && __ARM_ARCH > 6) ||       \
      defined(__ARM_ARCH_6K__)
  #ifdef __CC_ARM
    __yield();
  #else
    __asm__ __volatile__("yield");
  #endif
  #elif (defined(__mips64) || defined(__mips64__)) && defined(__mips_isa_rev) && \
      __mips_isa_rev >= 2
    __asm__ __volatile__("pause");
  #elif defined(__mips) || defined(__mips__) || defined(__mips64) ||             \
      defined(__mips64__) || defined(_M_MRX000) || defined(_MIPS_) ||            \
      defined(__MWERKS__) || defined(__sgi)
    __asm__ __volatile__(".word 0x00000140");
  #elif defined(__linux__) || defined(__gnu_linux__) || defined(_UNIX03_SOURCE)
    sched_yield();
  #elif (defined(_GNU_SOURCE) && __GLIBC_PREREQ(2, 1)) || defined(_OPEN_THREADS)
    pthread_yield();
  #endif
  }
  
  #if MDBX_64BIT_CAS
  static __always_inline bool atomic_cas64(volatile uint64_t *p, uint64_t c,
                                           uint64_t v) {
  #if !defined(__STDC_NO_ATOMICS__) &&                                           \
      (defined(ATOMIC_VAR_INIT) || defined(ATOMIC_LLONG_LOCK_FREE) ||            \
       __has_extension(c_atomic))
    STATIC_ASSERT(sizeof(long long) >= sizeof(uint64_t));
  #ifdef ATOMIC_LLONG_LOCK_FREE
    STATIC_ASSERT(ATOMIC_LLONG_LOCK_FREE > 0);
  #if ATOMIC_LLONG_LOCK_FREE < 2
    assert(atomic_is_lock_free(p));
  #endif
  #else
    assert(atomic_is_lock_free(p));
  #endif
  #ifdef __clang__
    STATIC_ASSERT(sizeof(_Atomic uint64_t) == sizeof(uint64_t));
    return atomic_compare_exchange_strong((_Atomic volatile uint64_t *)p, &c, v);
  #else
    return atomic_compare_exchange_strong(p, &c, v);
  #endif
  #elif defined(__GNUC__) || defined(__clang__)
    return __sync_bool_compare_and_swap(p, c, v);
  #elif defined(_MSC_VER)
    return c ==
           (uint64_t)_InterlockedCompareExchange64((volatile int64_t *)p, v, c);
  #elif defined(__APPLE__)
    return OSAtomicCompareAndSwap64Barrier(c, v, (volatile uint64_t *)p);
  #else
  #error FIXME: Unsupported compiler
  #endif
  }
  #endif /* MDBX_64BIT_CAS */
  
  static __always_inline bool atomic_cas32(volatile uint32_t *p, uint32_t c,
                                           uint32_t v) {
  #if !defined(__STDC_NO_ATOMICS__) &&                                           \
      (defined(ATOMIC_VAR_INIT) || defined(ATOMIC_INT_LOCK_FREE) ||              \
       __has_extension(c_atomic))
    STATIC_ASSERT(sizeof(int) >= sizeof(uint32_t));
  #ifdef ATOMIC_INT_LOCK_FREE
    STATIC_ASSERT(ATOMIC_INT_LOCK_FREE > 0);
  #if ATOMIC_INT_LOCK_FREE < 2
    assert(atomic_is_lock_free(p));
  #endif
  #else
    assert(atomic_is_lock_free(p));
  #endif
  #ifdef __clang__
    STATIC_ASSERT(sizeof(_Atomic uint32_t) == sizeof(uint32_t));
    return atomic_compare_exchange_strong((_Atomic volatile uint32_t *)p, &c, v);
  #else
    return atomic_compare_exchange_strong(p, &c, v);
  #endif
  #elif defined(__GNUC__) || defined(__clang__)
    return __sync_bool_compare_and_swap(p, c, v);
  #elif defined(_MSC_VER)
    STATIC_ASSERT(sizeof(volatile long) == sizeof(volatile uint32_t));
    return c == (uint32_t)_InterlockedCompareExchange((volatile long *)p, v, c);
  #elif defined(__APPLE__)
    return OSAtomicCompareAndSwap32Barrier(c, v, (volatile int32_t *)p);
  #else
  #error FIXME: Unsupported compiler
  #endif
  }
  
  static __always_inline uint32_t atomic_add32(volatile uint32_t *p, uint32_t v) {
  #if !defined(__STDC_NO_ATOMICS__) &&                                           \
      (defined(ATOMIC_VAR_INIT) || defined(ATOMIC_INT_LOCK_FREE) ||              \
       __has_extension(c_atomic))
    STATIC_ASSERT(sizeof(int) >= sizeof(uint32_t));
  #ifdef ATOMIC_INT_LOCK_FREE
    STATIC_ASSERT(ATOMIC_INT_LOCK_FREE > 0);
  #if ATOMIC_INT_LOCK_FREE < 2
    assert(atomic_is_lock_free(p));
  #endif
  #else
    assert(atomic_is_lock_free(p));
  #endif
  #ifdef __clang__
    STATIC_ASSERT(sizeof(_Atomic uint32_t) == sizeof(uint32_t));
    return atomic_fetch_add((_Atomic volatile uint32_t *)p, v);
  #else
    return atomic_fetch_add(p, v);
  #endif
  #elif defined(__GNUC__) || defined(__clang__)
    return __sync_fetch_and_add(p, v);
  #elif defined(_MSC_VER)
    STATIC_ASSERT(sizeof(volatile long) == sizeof(volatile uint32_t));
    return _InterlockedExchangeAdd((volatile long *)p, v);
  #elif defined(__APPLE__)
    return OSAtomicAdd32Barrier(v, (volatile int32_t *)p);
  #else
  #error FIXME: Unsupported compiler
  #endif
  }
  
  #define atomic_sub32(p, v) atomic_add32(p, 0 - (v))
  
  static __maybe_unused __always_inline bool safe64_is_valid(uint64_t v) {
  #if MDBX_WORDBITS >= 64
    return v < SAFE64_INVALID_THRESHOLD;
  #else
    return (v >> 32) != UINT32_MAX;
  #endif /* MDBX_WORDBITS */
  }
  
  static __maybe_unused __always_inline bool
  safe64_is_valid_ptr(const mdbx_safe64_t *ptr) {
    mdbx_compiler_barrier();
  #if MDBX_64BIT_ATOMIC
    return ptr->atomic < SAFE64_INVALID_THRESHOLD;
  #else
    return ptr->high != UINT32_MAX;
  #endif /* MDBX_64BIT_ATOMIC */
  }
  
  static __always_inline uint64_t safe64_txnid_next(uint64_t txnid) {
    txnid += MDBX_TXNID_STEP;
  #if !MDBX_64BIT_CAS
    /* avoid overflow of low-part in safe64_reset() */
    txnid += (UINT32_MAX == (uint32_t)txnid);
  #endif
    return txnid;
  }
  
  static __always_inline void safe64_reset(mdbx_safe64_t *ptr,
                                           bool single_writer) {
    mdbx_compiler_barrier();
  #if !MDBX_64BIT_CAS
    if (!single_writer) {
      STATIC_ASSERT(MDBX_TXNID_STEP > 1);
      /* it is safe to increment low-part to avoid ABA, since MDBX_TXNID_STEP > 1
       * and overflow was preserved in safe64_txnid_next() */
      atomic_add32(&ptr->low, 1) /* avoid ABA in safe64_reset_compare() */;
      ptr->high = UINT32_MAX /* atomically make >= SAFE64_INVALID_THRESHOLD */;
      atomic_add32(&ptr->low, 1) /* avoid ABA in safe64_reset_compare() */;
    } else
  #else
    (void)single_writer;
  #endif /* !MDBX_64BIT_CAS */
  #if MDBX_64BIT_ATOMIC
      ptr->atomic = UINT64_MAX;
  #else
    /* atomically make value >= SAFE64_INVALID_THRESHOLD */
    ptr->high = UINT32_MAX;
  #endif /* MDBX_64BIT_ATOMIC */
    assert(ptr->inconsistent >= SAFE64_INVALID_THRESHOLD);
    mdbx_flush_incoherent_cpu_writeback();
    mdbx_jitter4testing(true);
  }
  
  static __always_inline bool safe64_reset_compare(mdbx_safe64_t *ptr,
                                                   txnid_t compare) {
    mdbx_compiler_barrier();
    /* LY: This function is used to reset `mr_txnid` from hsr-handler in case
     *     the asynchronously cancellation of read transaction. Therefore,
     *     there may be a collision between the cleanup performed here and
     *     asynchronous termination and restarting of the read transaction
     *     in another proces/thread. In general we MUST NOT reset the `mr_txnid`
     *     if a new transaction was started (i.e. if `mr_txnid` was changed). */
  #if MDBX_64BIT_CAS
    bool rc = atomic_cas64(&ptr->inconsistent, compare, UINT64_MAX);
    mdbx_flush_incoherent_cpu_writeback();
  #else
    /* LY: There is no gold ratio here since shared mutex is too costly,
     *     in such way we must acquire/release it for every update of mr_txnid,
     *     i.e. twice for each read transaction). */
    bool rc = false;
    if (likely(ptr->low == (uint32_t)compare &&
               atomic_cas32(&ptr->high, (uint32_t)(compare >> 32), UINT32_MAX))) {
      if (unlikely(ptr->low != (uint32_t)compare))
        atomic_cas32(&ptr->high, UINT32_MAX, (uint32_t)(compare >> 32));
      else
        rc = true;
    }
  #endif /* MDBX_64BIT_CAS */
    mdbx_jitter4testing(true);
    return rc;
  }
  
  static __always_inline void safe64_write(mdbx_safe64_t *ptr, const uint64_t v) {
    mdbx_compiler_barrier();
    assert(ptr->inconsistent >= SAFE64_INVALID_THRESHOLD);
  #if MDBX_64BIT_ATOMIC
    ptr->atomic = v;
  #else  /* MDBX_64BIT_ATOMIC */
    /* update low-part but still value >= SAFE64_INVALID_THRESHOLD */
    ptr->low = (uint32_t)v;
    assert(ptr->inconsistent >= SAFE64_INVALID_THRESHOLD);
    mdbx_flush_incoherent_cpu_writeback();
    mdbx_jitter4testing(true);
    /* update high-part from SAFE64_INVALID_THRESHOLD to actual value */
    ptr->high = (uint32_t)(v >> 32);
  #endif /* MDBX_64BIT_ATOMIC */
    assert(ptr->inconsistent == v);
    mdbx_flush_incoherent_cpu_writeback();
    mdbx_jitter4testing(true);
  }
  
  static __always_inline uint64_t safe64_read(const mdbx_safe64_t *ptr) {
    mdbx_compiler_barrier();
    mdbx_jitter4testing(true);
    uint64_t v;
  #if MDBX_64BIT_ATOMIC
    v = ptr->atomic;
  #else  /* MDBX_64BIT_ATOMIC */
    uint32_t hi, lo;
    do {
      hi = ptr->high;
      mdbx_compiler_barrier();
      mdbx_jitter4testing(true);
      lo = ptr->low;
      mdbx_compiler_barrier();
      mdbx_jitter4testing(true);
    } while (unlikely(hi != ptr->high));
    v = lo | (uint64_t)hi << 32;
  #endif /* MDBX_64BIT_ATOMIC */
    mdbx_jitter4testing(true);
    return v;
  }
  
  static __always_inline void safe64_update(mdbx_safe64_t *ptr,
                                            const uint64_t v) {
    safe64_reset(ptr, true);
    safe64_write(ptr, v);
  }
  
  /*----------------------------------------------------------------------------*/
  /* rthc (tls keys and destructors) */
  
  typedef struct rthc_entry_t {
    MDBX_reader *begin;
    MDBX_reader *end;
    mdbx_thread_key_t thr_tls_key;
    bool key_valid;
  } rthc_entry_t;
  
  #if MDBX_DEBUG
  #define RTHC_INITIAL_LIMIT 1
  #else
  #define RTHC_INITIAL_LIMIT 16
  #endif
  
  static bin128_t bootid;
  
  #if defined(_WIN32) || defined(_WIN64)
  static CRITICAL_SECTION rthc_critical_section;
  static CRITICAL_SECTION lcklist_critical_section;
  #else
  int __cxa_thread_atexit_impl(void (*dtor)(void *), void *obj, void *dso_symbol)
      __attribute__((__weak__));
  #ifdef __APPLE__ /* FIXME: Thread-Local Storage destructors & DSO-unloading */
  int __cxa_thread_atexit_impl(void (*dtor)(void *), void *obj,
                               void *dso_symbol) {
    (void)dtor;
    (void)obj;
    (void)dso_symbol;
    return -1;
  }
  #endif           /* __APPLE__ */
  
  static pthread_mutex_t lcklist_mutex = PTHREAD_MUTEX_INITIALIZER;
  static pthread_mutex_t rthc_mutex = PTHREAD_MUTEX_INITIALIZER;
  static pthread_cond_t rthc_cond = PTHREAD_COND_INITIALIZER;
  static mdbx_thread_key_t rthc_key;
  static volatile uint32_t rthc_pending;
  
  static void __cold workaround_glibc_bug21031(void) {
    /* Workaround for https://sourceware.org/bugzilla/show_bug.cgi?id=21031
     *
     * Due race between pthread_key_delete() and __nptl_deallocate_tsd()
     * The destructor(s) of thread-local-storage object(s) may be running
     * in another thread(s) and be blocked or not finished yet.
     * In such case we get a SEGFAULT after unload this library DSO.
     *
     * So just by yielding a few timeslices we give a chance
     * to such destructor(s) for completion and avoids segfault. */
    sched_yield();
    sched_yield();
    sched_yield();
  }
  #endif
  
  static unsigned rthc_count, rthc_limit;
  static rthc_entry_t *rthc_table;
  static rthc_entry_t rthc_table_static[RTHC_INITIAL_LIMIT];
  
  static __inline void rthc_lock(void) {
  #if defined(_WIN32) || defined(_WIN64)
    EnterCriticalSection(&rthc_critical_section);
  #else
    mdbx_ensure(nullptr, pthread_mutex_lock(&rthc_mutex) == 0);
  #endif
  }
  
  static __inline void rthc_unlock(void) {
  #if defined(_WIN32) || defined(_WIN64)
    LeaveCriticalSection(&rthc_critical_section);
  #else
    mdbx_ensure(nullptr, pthread_mutex_unlock(&rthc_mutex) == 0);
  #endif
  }
  
  static __inline int thread_key_create(mdbx_thread_key_t *key) {
    int rc;
  #if defined(_WIN32) || defined(_WIN64)
    *key = TlsAlloc();
    rc = (*key != TLS_OUT_OF_INDEXES) ? MDBX_SUCCESS : GetLastError();
  #else
    rc = pthread_key_create(key, nullptr);
  #endif
    mdbx_trace("&key = %p, value %" PRIuPTR ", rc %d",
               __Wpedantic_format_voidptr(key), (uintptr_t)*key, rc);
    return rc;
  }
  
  static __inline void thread_key_delete(mdbx_thread_key_t key) {
    mdbx_trace("key = %" PRIuPTR, (uintptr_t)key);
  #if defined(_WIN32) || defined(_WIN64)
    mdbx_ensure(nullptr, TlsFree(key));
  #else
    mdbx_ensure(nullptr, pthread_key_delete(key) == 0);
    workaround_glibc_bug21031();
  #endif
  }
  
  static __inline void *thread_rthc_get(mdbx_thread_key_t key) {
  #if defined(_WIN32) || defined(_WIN64)
    return TlsGetValue(key);
  #else
    return pthread_getspecific(key);
  #endif
  }
  
  static void thread_rthc_set(mdbx_thread_key_t key, const void *value) {
  #if defined(_WIN32) || defined(_WIN64)
    mdbx_ensure(nullptr, TlsSetValue(key, (void *)value));
  #else
  #define MDBX_THREAD_RTHC_ZERO 0
  #define MDBX_THREAD_RTHC_REGISTERED 1
  #define MDBX_THREAD_RTHC_COUNTED 2
    static __thread uint32_t thread_registration_state;
    if (value && unlikely(thread_registration_state == MDBX_THREAD_RTHC_ZERO)) {
      thread_registration_state = MDBX_THREAD_RTHC_REGISTERED;
      mdbx_trace("thread registered 0x%" PRIxPTR, mdbx_thread_self());
      if (&__cxa_thread_atexit_impl == nullptr ||
          __cxa_thread_atexit_impl(mdbx_rthc_thread_dtor,
                                   &thread_registration_state,
                                   (void *)&mdbx_version /* dso_anchor */)) {
        mdbx_ensure(nullptr, pthread_setspecific(
                                 rthc_key, &thread_registration_state) == 0);
        thread_registration_state = MDBX_THREAD_RTHC_COUNTED;
        const unsigned count_before = atomic_add32(&rthc_pending, 1);
        mdbx_ensure(nullptr, count_before < INT_MAX);
        mdbx_trace("fallback to pthreads' tsd, key %" PRIuPTR ", count %u",
                   (uintptr_t)rthc_key, count_before);
        (void)count_before;
      }
    }
    mdbx_ensure(nullptr, pthread_setspecific(key, value) == 0);
  #endif
  }
  
  __cold void mdbx_rthc_global_init(void) {
    rthc_limit = RTHC_INITIAL_LIMIT;
    rthc_table = rthc_table_static;
  #if defined(_WIN32) || defined(_WIN64)
    InitializeCriticalSection(&rthc_critical_section);
    InitializeCriticalSection(&lcklist_critical_section);
  #else
    mdbx_ensure(nullptr,
                pthread_key_create(&rthc_key, mdbx_rthc_thread_dtor) == 0);
    mdbx_trace("pid %d, &mdbx_rthc_key = %p, value 0x%x", mdbx_getpid(),
               __Wpedantic_format_voidptr(&rthc_key), (unsigned)rthc_key);
  #endif
    /* checking time conversion, this also avoids racing on 32-bit architectures
     * during writing calculated 64-bit ratio(s) into memory. */
    uint32_t proba = UINT32_MAX;
    while (true) {
      unsigned time_conversion_checkup =
          mdbx_osal_monotime_to_16dot16(mdbx_osal_16dot16_to_monotime(proba));
      unsigned one_more = (proba < UINT32_MAX) ? proba + 1 : proba;
      unsigned one_less = (proba > 0) ? proba - 1 : proba;
      mdbx_ensure(nullptr, time_conversion_checkup >= one_less &&
                               time_conversion_checkup <= one_more);
      if (proba == 0)
        break;
      proba >>= 1;
    }
  
    bootid = mdbx_osal_bootid();
  }
  
  /* dtor called for thread, i.e. for all mdbx's environment objects */
  __cold void mdbx_rthc_thread_dtor(void *ptr) {
    rthc_lock();
    mdbx_trace(">> pid %d, thread 0x%" PRIxPTR ", rthc %p", mdbx_getpid(),
               mdbx_thread_self(), ptr);
  
    const uint32_t self_pid = mdbx_getpid();
    for (unsigned i = 0; i < rthc_count; ++i) {
      if (!rthc_table[i].key_valid)
        continue;
      const mdbx_thread_key_t key = rthc_table[i].thr_tls_key;
      MDBX_reader *const rthc = thread_rthc_get(key);
      if (rthc < rthc_table[i].begin || rthc >= rthc_table[i].end)
        continue;
  #if !defined(_WIN32) && !defined(_WIN64)
      if (pthread_setspecific(key, nullptr) != 0) {
        mdbx_trace("== thread 0x%" PRIxPTR
                   ", rthc %p: ignore race with tsd-key deletion",
                   mdbx_thread_self(), ptr);
        continue /* ignore race with tsd-key deletion by mdbx_env_close() */;
      }
  #endif
  
      mdbx_trace("== thread 0x%" PRIxPTR
                 ", rthc %p, [%i], %p ... %p (%+i), rtch-pid %i, "
                 "current-pid %i",
                 mdbx_thread_self(), __Wpedantic_format_voidptr(rthc), i,
                 __Wpedantic_format_voidptr(rthc_table[i].begin),
                 __Wpedantic_format_voidptr(rthc_table[i].end),
                 (int)(rthc - rthc_table[i].begin), rthc->mr_pid, self_pid);
      if (rthc->mr_pid == self_pid) {
        mdbx_trace("==== thread 0x%" PRIxPTR ", rthc %p, cleanup",
                   mdbx_thread_self(), __Wpedantic_format_voidptr(rthc));
        rthc->mr_pid = 0;
      }
    }
  
  #if defined(_WIN32) || defined(_WIN64)
    mdbx_trace("<< thread 0x%" PRIxPTR ", rthc %p", mdbx_thread_self(), ptr);
    rthc_unlock();
  #else
    const char self_registration = *(char *)ptr;
    *(char *)ptr = MDBX_THREAD_RTHC_ZERO;
    mdbx_trace("== thread 0x%" PRIxPTR ", rthc %p, pid %d, self-status %d",
               mdbx_thread_self(), ptr, mdbx_getpid(), self_registration);
    if (self_registration == MDBX_THREAD_RTHC_COUNTED)
      mdbx_ensure(nullptr, atomic_sub32(&rthc_pending, 1) > 0);
  
    if (rthc_pending == 0) {
      mdbx_trace("== thread 0x%" PRIxPTR ", rthc %p, pid %d, wake",
                 mdbx_thread_self(), ptr, mdbx_getpid());
      mdbx_ensure(nullptr, pthread_cond_broadcast(&rthc_cond) == 0);
    }
  
    mdbx_trace("<< thread 0x%" PRIxPTR ", rthc %p", mdbx_thread_self(), ptr);
    /* Allow tail call optimization, i.e. gcc should generate the jmp instruction
     * instead of a call for pthread_mutex_unlock() and therefore CPU could not
     * return to current DSO's code section, which may be unloaded immediately
     * after the mutex got released. */
    pthread_mutex_unlock(&rthc_mutex);
  #endif
  }
  
  __cold void mdbx_rthc_global_dtor(void) {
    mdbx_trace(">> pid %d", mdbx_getpid());
  
    rthc_lock();
  #if !defined(_WIN32) && !defined(_WIN64)
    char *rthc = (char *)pthread_getspecific(rthc_key);
    mdbx_trace("== thread 0x%" PRIxPTR ", rthc %p, pid %d, self-status %d",
               mdbx_thread_self(), __Wpedantic_format_voidptr(rthc),
               mdbx_getpid(), rthc ? *rthc : -1);
    if (rthc) {
      const char self_registration = *(char *)rthc;
      *rthc = MDBX_THREAD_RTHC_ZERO;
      if (self_registration == MDBX_THREAD_RTHC_COUNTED)
        mdbx_ensure(nullptr, atomic_sub32(&rthc_pending, 1) > 0);
    }
  
    struct timespec abstime;
    mdbx_ensure(nullptr, clock_gettime(CLOCK_REALTIME, &abstime) == 0);
    abstime.tv_nsec += 1000000000l / 10;
    if (abstime.tv_nsec >= 1000000000l) {
      abstime.tv_nsec -= 1000000000l;
      abstime.tv_sec += 1;
    }
  #if MDBX_DEBUG > 0
    abstime.tv_sec += 600;
  #endif
  
    for (unsigned left; (left = rthc_pending) > 0;) {
      mdbx_trace("pid %d, pending %u, wait for...", mdbx_getpid(), left);
      const int rc = pthread_cond_timedwait(&rthc_cond, &rthc_mutex, &abstime);
      if (rc && rc != EINTR)
        break;
    }
    thread_key_delete(rthc_key);
  #endif
  
    const uint32_t self_pid = mdbx_getpid();
    for (unsigned i = 0; i < rthc_count; ++i) {
      if (!rthc_table[i].key_valid)
        continue;
      const mdbx_thread_key_t key = rthc_table[i].thr_tls_key;
      thread_key_delete(key);
      for (MDBX_reader *rthc = rthc_table[i].begin; rthc < rthc_table[i].end;
           ++rthc) {
        mdbx_trace("== [%i] = key %" PRIuPTR ", %p ... %p, rthc %p (%+i), "
                   "rthc-pid %i, current-pid %i",
                   i, (uintptr_t)key,
                   __Wpedantic_format_voidptr(rthc_table[i].begin),
                   __Wpedantic_format_voidptr(rthc_table[i].end),
                   __Wpedantic_format_voidptr(rthc),
                   (int)(rthc - rthc_table[i].begin), rthc->mr_pid, self_pid);
        if (rthc->mr_pid == self_pid) {
          rthc->mr_pid = 0;
          mdbx_trace("== cleanup %p", __Wpedantic_format_voidptr(rthc));
        }
      }
    }
  
    rthc_limit = rthc_count = 0;
    if (rthc_table != rthc_table_static)
      mdbx_free(rthc_table);
    rthc_table = nullptr;
    rthc_unlock();
  
  #if defined(_WIN32) || defined(_WIN64)
    DeleteCriticalSection(&lcklist_critical_section);
    DeleteCriticalSection(&rthc_critical_section);
  #else
    /* LY: yielding a few timeslices to give a more chance
     * to racing destructor(s) for completion. */
    workaround_glibc_bug21031();
  #endif
  
    mdbx_trace("<< pid %d\n", mdbx_getpid());
  }
  
  __cold int mdbx_rthc_alloc(mdbx_thread_key_t *key, MDBX_reader *begin,
                             MDBX_reader *end) {
    int rc;
    if (key) {
  #ifndef NDEBUG
      *key = (mdbx_thread_key_t)0xBADBADBAD;
  #endif /* NDEBUG */
      rc = thread_key_create(key);
      if (rc != MDBX_SUCCESS)
        return rc;
    }
  
    rthc_lock();
    const mdbx_thread_key_t new_key = key ? *key : 0;
    mdbx_trace(">> key %" PRIuPTR ", rthc_count %u, rthc_limit %u",
               (uintptr_t)new_key, rthc_count, rthc_limit);
    if (rthc_count == rthc_limit) {
      rthc_entry_t *new_table =
          mdbx_realloc((rthc_table == rthc_table_static) ? nullptr : rthc_table,
                       sizeof(rthc_entry_t) * rthc_limit * 2);
      if (new_table == nullptr) {
        rc = MDBX_ENOMEM;
        goto bailout;
      }
      if (rthc_table == rthc_table_static)
        memcpy(new_table, rthc_table_static, sizeof(rthc_table_static));
      rthc_table = new_table;
      rthc_limit *= 2;
    }
    mdbx_trace("== [%i] = key %" PRIuPTR ", %p ... %p", rthc_count,
               (uintptr_t)new_key, __Wpedantic_format_voidptr(begin),
               __Wpedantic_format_voidptr(end));
    rthc_table[rthc_count].key_valid = key ? true : false;
    rthc_table[rthc_count].thr_tls_key = key ? new_key : 0;
    rthc_table[rthc_count].begin = begin;
    rthc_table[rthc_count].end = end;
    ++rthc_count;
    mdbx_trace("<< key %" PRIuPTR ", rthc_count %u, rthc_limit %u",
               (uintptr_t)new_key, rthc_count, rthc_limit);
    rthc_unlock();
    return MDBX_SUCCESS;
  
  bailout:
    if (key)
      thread_key_delete(*key);
    rthc_unlock();
    return rc;
  }
  
  __cold void mdbx_rthc_remove(const mdbx_thread_key_t key) {
    thread_key_delete(key);
    rthc_lock();
    mdbx_trace(">> key %zu, rthc_count %u, rthc_limit %u", (size_t)key,
               rthc_count, rthc_limit);
  
    for (unsigned i = 0; i < rthc_count; ++i) {
      if (rthc_table[i].key_valid && key == rthc_table[i].thr_tls_key) {
        const uint32_t self_pid = mdbx_getpid();
        mdbx_trace("== [%i], %p ...%p, current-pid %d", i,
                   __Wpedantic_format_voidptr(rthc_table[i].begin),
                   __Wpedantic_format_voidptr(rthc_table[i].end), self_pid);
  
        for (MDBX_reader *rthc = rthc_table[i].begin; rthc < rthc_table[i].end;
             ++rthc) {
          if (rthc->mr_pid == self_pid) {
            rthc->mr_pid = 0;
            mdbx_trace("== cleanup %p", __Wpedantic_format_voidptr(rthc));
          }
        }
        if (--rthc_count > 0)
          rthc_table[i] = rthc_table[rthc_count];
        else if (rthc_table != rthc_table_static) {
          mdbx_free(rthc_table);
          rthc_table = rthc_table_static;
          rthc_limit = RTHC_INITIAL_LIMIT;
        }
        break;
      }
    }
  
    mdbx_trace("<< key %zu, rthc_count %u, rthc_limit %u", (size_t)key,
               rthc_count, rthc_limit);
    rthc_unlock();
  }
  
  //------------------------------------------------------------------------------
  
  #define RTHC_ENVLIST_END ((MDBX_env *)((uintptr_t)50459))
  static MDBX_env *inprocess_lcklist_head = RTHC_ENVLIST_END;
  
  static __inline void lcklist_lock(void) {
  #if defined(_WIN32) || defined(_WIN64)
    EnterCriticalSection(&lcklist_critical_section);
  #else
    mdbx_ensure(nullptr, pthread_mutex_lock(&lcklist_mutex) == 0);
  #endif
  }
  
  static __inline void lcklist_unlock(void) {
  #if defined(_WIN32) || defined(_WIN64)
    LeaveCriticalSection(&lcklist_critical_section);
  #else
    mdbx_ensure(nullptr, pthread_mutex_unlock(&lcklist_mutex) == 0);
  #endif
  }
  
  MDBX_NOTHROW_CONST_FUNCTION static uint64_t rrxmrrxmsx_0(uint64_t v) {
    /* Pelle Evensen's mixer, https://bit.ly/2HOfynt */
    v ^= (v << 39 | v >> 25) ^ (v << 14 | v >> 50);
    v *= UINT64_C(0xA24BAED4963EE407);
    v ^= (v << 40 | v >> 24) ^ (v << 15 | v >> 49);
    v *= UINT64_C(0x9FB21C651E98DF25);
    return v ^ v >> 28;
  }
  
  static int uniq_peek(const mdbx_mmap_t *pending, mdbx_mmap_t *scan) {
    int rc;
    uint64_t bait;
    if (pending->address) {
      bait = pending->lck->mti_bait_uniqueness;
      rc = MDBX_SUCCESS;
    } else {
      bait = 0 /* hush MSVC warning */;
      rc = mdbx_msync(scan, 0, sizeof(MDBX_lockinfo), true);
      if (rc == MDBX_SUCCESS)
        rc =
            mdbx_pread(pending->fd, &bait, sizeof(scan->lck->mti_bait_uniqueness),
                       offsetof(MDBX_lockinfo, mti_bait_uniqueness));
    }
    if (likely(rc == MDBX_SUCCESS) && bait == scan->lck->mti_bait_uniqueness)
      rc = MDBX_RESULT_TRUE;
  
    mdbx_trace("uniq-peek: %s, bait 0x%016" PRIx64 ",%s rc %d",
               pending->lck ? "mem" : "file", bait,
               (rc == MDBX_RESULT_TRUE) ? " found," : (rc ? " FAILED," : ""), rc);
    return rc;
  }
  
  static int uniq_poke(const mdbx_mmap_t *pending, mdbx_mmap_t *scan,
                       uint64_t *abra) {
    if (*abra == 0) {
      const uintptr_t tid = mdbx_thread_self();
      uintptr_t uit = 0;
      memcpy(&uit, &tid, (sizeof(tid) < sizeof(uit)) ? sizeof(tid) : sizeof(uit));
      *abra =
          rrxmrrxmsx_0(mdbx_osal_monotime() + UINT64_C(5873865991930747) * uit);
    }
    const uint64_t cadabra =
        rrxmrrxmsx_0(*abra + UINT64_C(7680760450171793) * (unsigned)mdbx_getpid())
            << 24 |
        *abra >> 40;
    scan->lck->mti_bait_uniqueness = cadabra;
    mdbx_flush_incoherent_cpu_writeback();
    *abra = *abra * UINT64_C(6364136223846793005) + 1;
    return uniq_peek(pending, scan);
  }
  
  __cold static int uniq_check(const mdbx_mmap_t *pending, MDBX_env **found) {
    *found = nullptr;
    uint64_t salt = 0;
    for (MDBX_env *scan = inprocess_lcklist_head; scan != RTHC_ENVLIST_END;
         scan = scan->me_lcklist_next) {
      int err = scan->me_lck_mmap.lck->mti_bait_uniqueness
                    ? uniq_peek(pending, &scan->me_lck_mmap)
                    : uniq_poke(pending, &scan->me_lck_mmap, &salt);
      if (err == MDBX_ENODATA) {
        uint64_t length;
        if (likely(mdbx_filesize(pending->fd, &length) == MDBX_SUCCESS &&
                   length == 0)) {
          /* LY: skip checking since LCK-file is empty, i.e. just created. */
          mdbx_debug("uniq-probe: %s", "unique (new/empty lck)");
          return MDBX_RESULT_TRUE;
        }
      }
      if (err == MDBX_RESULT_TRUE)
        err = uniq_poke(pending, &scan->me_lck_mmap, &salt);
      if (err == MDBX_RESULT_TRUE) {
        (void)mdbx_msync(&scan->me_lck_mmap, 0, sizeof(MDBX_lockinfo), false);
        err = uniq_poke(pending, &scan->me_lck_mmap, &salt);
      }
      if (err == MDBX_RESULT_TRUE) {
        err = uniq_poke(pending, &scan->me_lck_mmap, &salt);
        *found = scan;
        mdbx_debug("uniq-probe: found %p", __Wpedantic_format_voidptr(*found));
        return MDBX_RESULT_FALSE;
      }
      if (unlikely(err != MDBX_SUCCESS)) {
        mdbx_debug("uniq-probe: failed rc %d", err);
        return err;
      }
    }
  
    mdbx_debug("uniq-probe: %s", "unique");
    return MDBX_RESULT_TRUE;
  }
  
  static int lcklist_detach_locked(MDBX_env *env) {
    MDBX_env *inprocess_neighbor = nullptr;
    int rc = MDBX_SUCCESS;
    if (env->me_lcklist_next != nullptr) {
      mdbx_ensure(env, env->me_lcklist_next != nullptr);
      mdbx_ensure(env, inprocess_lcklist_head != RTHC_ENVLIST_END);
      for (MDBX_env **ptr = &inprocess_lcklist_head; *ptr != RTHC_ENVLIST_END;
           ptr = &(*ptr)->me_lcklist_next) {
        if (*ptr == env) {
          *ptr = env->me_lcklist_next;
          env->me_lcklist_next = nullptr;
          break;
        }
      }
      mdbx_ensure(env, env->me_lcklist_next == nullptr);
    }
  
    rc = likely(mdbx_getpid() == env->me_pid)
             ? uniq_check(&env->me_lck_mmap, &inprocess_neighbor)
             : MDBX_PANIC;
    if (!inprocess_neighbor && env->me_live_reader)
      (void)mdbx_rpid_clear(env);
    if (!MDBX_IS_ERROR(rc))
      rc = mdbx_lck_destroy(env, inprocess_neighbor);
    return rc;
  }
  
  /*------------------------------------------------------------------------------
   * LY: State of the art quicksort-based sorting, with internal stack
   * and network-sort for small chunks.
   * Thanks to John M. Gamble for the http://pages.ripco.net/~jgamble/nw.html */
  
  #define SORT_CMP_SWAP(TYPE, CMP, a, b)                                         \
    do {                                                                         \
      const TYPE swap_tmp = (a);                                                 \
      const bool swap_cmp = CMP(swap_tmp, b);                                    \
      (a) = swap_cmp ? swap_tmp : b;                                             \
      (b) = swap_cmp ? b : swap_tmp;                                             \
    } while (0)
  
  //  3 comparators, 3 parallel operations
  //  o-----^--^--o
  //        |  |
  //  o--^--|--v--o
  //     |  |
  //  o--v--v-----o
  //
  //  [[1,2]]
  //  [[0,2]]
  //  [[0,1]]
  #define SORT_NETWORK_3(TYPE, CMP, begin)                                       \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
    } while (0)
  
  //  5 comparators, 3 parallel operations
  //  o--^--^--------o
  //     |  |
  //  o--v--|--^--^--o
  //        |  |  |
  //  o--^--v--|--v--o
  //     |     |
  //  o--v-----v-----o
  //
  //  [[0,1],[2,3]]
  //  [[0,2],[1,3]]
  //  [[1,2]]
  #define SORT_NETWORK_4(TYPE, CMP, begin)                                       \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
    } while (0)
  
  //  9 comparators, 5 parallel operations
  //  o--^--^-----^-----------o
  //     |  |     |
  //  o--|--|--^--v-----^--^--o
  //     |  |  |        |  |
  //  o--|--v--|--^--^--|--v--o
  //     |     |  |  |  |
  //  o--|-----v--|--v--|--^--o
  //     |        |     |  |
  //  o--v--------v-----v--v--o
  //
  //  [[0,4],[1,3]]
  //  [[0,2]]
  //  [[2,4],[0,1]]
  //  [[2,3],[1,4]]
  //  [[1,2],[3,4]]
  #define SORT_NETWORK_5(TYPE, CMP, begin)                                       \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
    } while (0)
  
  //  12 comparators, 6 parallel operations
  //  o-----^--^--^-----------------o
  //        |  |  |
  //  o--^--|--v--|--^--------^-----o
  //     |  |     |  |        |
  //  o--v--v-----|--|--^--^--|--^--o
  //              |  |  |  |  |  |
  //  o-----^--^--v--|--|--|--v--v--o
  //        |  |     |  |  |
  //  o--^--|--v-----v--|--v--------o
  //     |  |           |
  //  o--v--v-----------v-----------o
  //
  //  [[1,2],[4,5]]
  //  [[0,2],[3,5]]
  //  [[0,1],[3,4],[2,5]]
  //  [[0,3],[1,4]]
  //  [[2,4],[1,3]]
  //  [[2,3]]
  #define SORT_NETWORK_6(TYPE, CMP, begin)                                       \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
    } while (0)
  
  //  16 comparators, 6 parallel operations
  //  o--^--------^-----^-----------------o
  //     |        |     |
  //  o--|--^-----|--^--v--------^--^-----o
  //     |  |     |  |           |  |
  //  o--|--|--^--v--|--^-----^--|--v-----o
  //     |  |  |     |  |     |  |
  //  o--|--|--|-----v--|--^--v--|--^--^--o
  //     |  |  |        |  |     |  |  |
  //  o--v--|--|--^-----v--|--^--v--|--v--o
  //        |  |  |        |  |     |
  //  o-----v--|--|--------v--v-----|--^--o
  //           |  |                 |  |
  //  o--------v--v-----------------v--v--o
  //
  //  [[0,4],[1,5],[2,6]]
  //  [[0,2],[1,3],[4,6]]
  //  [[2,4],[3,5],[0,1]]
  //  [[2,3],[4,5]]
  //  [[1,4],[3,6]]
  //  [[1,2],[3,4],[5,6]]
  #define SORT_NETWORK_7(TYPE, CMP, begin)                                       \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
    } while (0)
  
  //  19 comparators, 6 parallel operations
  //  o--^--------^-----^-----------------o
  //     |        |     |
  //  o--|--^-----|--^--v--------^--^-----o
  //     |  |     |  |           |  |
  //  o--|--|--^--v--|--^-----^--|--v-----o
  //     |  |  |     |  |     |  |
  //  o--|--|--|--^--v--|--^--v--|--^--^--o
  //     |  |  |  |     |  |     |  |  |
  //  o--v--|--|--|--^--v--|--^--v--|--v--o
  //        |  |  |  |     |  |     |
  //  o-----v--|--|--|--^--v--v-----|--^--o
  //           |  |  |  |           |  |
  //  o--------v--|--v--|--^--------v--v--o
  //              |     |  |
  //  o-----------v-----v--v--------------o
  //
  //  [[0,4],[1,5],[2,6],[3,7]]
  //  [[0,2],[1,3],[4,6],[5,7]]
  //  [[2,4],[3,5],[0,1],[6,7]]
  //  [[2,3],[4,5]]
  //  [[1,4],[3,6]]
  //  [[1,2],[3,4],[5,6]]
  #define SORT_NETWORK_8(TYPE, CMP, begin)                                       \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
    } while (0)
  
  //  25 comparators, 9 parallel operations
  //  o--^-----^--^-----^-----------------------------------o
  //     |     |  |     |
  //  o--v--^--v--|-----|--^-----^-----------^--------------o
  //        |     |     |  |     |           |
  //  o-----v-----|-----|--|-----|--^-----^--|--^-----^--^--o
  //              |     |  |     |  |     |  |  |     |  |
  //  o--^-----^--v--^--v--|-----|--|-----|--v--|-----|--v--o
  //     |     |     |     |     |  |     |     |     |
  //  o--v--^--v-----|-----v--^--v--|-----|-----|--^--v-----o
  //        |        |        |     |     |     |  |
  //  o-----v--------|--------|-----v--^--v--^--|--|--^-----o
  //                 |        |        |     |  |  |  |
  //  o--^-----^-----v--------|--------|-----|--v--v--v-----o
  //     |     |              |        |     |
  //  o--v--^--v--------------v--------|-----v--------------o
  //        |                          |
  //  o-----v--------------------------v--------------------o
  //
  //  [[0,1],[3,4],[6,7]]
  //  [[1,2],[4,5],[7,8]]
  //  [[0,1],[3,4],[6,7],[2,5]]
  //  [[0,3],[1,4],[5,8]]
  //  [[3,6],[4,7],[2,5]]
  //  [[0,3],[1,4],[5,7],[2,6]]
  //  [[1,3],[4,6]]
  //  [[2,4],[5,6]]
  //  [[2,3]]
  #define SORT_NETWORK_9(TYPE, CMP, begin)                                       \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
    } while (0)
  
  //  29 comparators, 9 parallel operations
  //  o--------------^-----^--^--^-----------------------o
  //                 |     |  |  |
  //  o-----------^--|--^--|--|--v--^--------^-----------o
  //              |  |  |  |  |     |        |
  //  o--------^--|--|--|--|--v--^--v-----^--|--^--------o
  //           |  |  |  |  |     |        |  |  |
  //  o-----^--|--|--|--|--v--^--|-----^--|--v--v--^-----o
  //        |  |  |  |  |     |  |     |  |        |
  //  o--^--|--|--|--|--v-----|--v--^--|--|--^-----v--^--o
  //     |  |  |  |  |        |     |  |  |  |        |
  //  o--|--|--|--|--v--^-----|--^--|--v--v--|-----^--v--o
  //     |  |  |  |     |     |  |  |        |     |
  //  o--|--|--|--v--^--|-----v--|--v--^-----|--^--v-----o
  //     |  |  |     |  |        |     |     |  |
  //  o--|--|--v-----|--|--^-----v--^--|-----v--v--------o
  //     |  |        |  |  |        |  |
  //  o--|--v--------|--v--|--^-----v--v-----------------o
  //     |           |     |  |
  //  o--v-----------v-----v--v--------------------------o
  //
  //  [[4,9],[3,8],[2,7],[1,6],[0,5]]
  //  [[1,4],[6,9],[0,3],[5,8]]
  //  [[0,2],[3,6],[7,9]]
  //  [[0,1],[2,4],[5,7],[8,9]]
  //  [[1,2],[4,6],[7,8],[3,5]]
  //  [[2,5],[6,8],[1,3],[4,7]]
  //  [[2,3],[6,7]]
  //  [[3,4],[5,6]]
  //  [[4,5]]
  #define SORT_NETWORK_10(TYPE, CMP, begin)                                      \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
    } while (0)
  
  //  35 comparators, 9 parallel operations
  //  o--^-----^-----------------^--------^--------------------o
  //     |     |                 |        |
  //  o--v--^--|--^--^--------^--|--------|--^-----------------o
  //        |  |  |  |        |  |        |  |
  //  o--^--|--v--v--|-----^--|--|--------|--|-----^--^--------o
  //     |  |        |     |  |  |        |  |     |  |
  //  o--v--v--------|-----|--|--|--^-----|--|--^--v--|--^--^--o
  //                 |     |  |  |  |     |  |  |     |  |  |
  //  o--^-----^-----|-----|--|--v--|--^--v--v--|-----v--|--v--o
  //     |     |     |     |  |     |  |        |        |
  //  o--v--^--|--^--v--^--|--v-----|--|--------|--------v--^--o
  //        |  |  |     |  |        |  |        |           |
  //  o--^--|--v--v--^--|--v--^-----|--|--------|--------^--v--o
  //     |  |        |  |     |     |  |        |        |
  //  o--v--v--------|--|-----|-----v--|--^-----|-----^--|--^--o
  //                 |  |     |        |  |     |     |  |  |
  //  o--^--^--------|--|-----|--------v--|-----v--^--|--v--v--o
  //     |  |        |  |     |           |        |  |
  //  o--v--|--^-----|--v-----|-----------|--------v--v--------o
  //        |  |     |        |           |
  //  o-----v--v-----v--------v-----------v--------------------o
  //
  //  [[0,1],[2,3],[4,5],[6,7],[8,9]]
  //  [[1,3],[5,7],[0,2],[4,6],[8,10]]
  //  [[1,2],[5,6],[9,10],[0,4],[3,7]]
  //  [[1,5],[6,10],[4,8]]
  //  [[5,9],[2,6],[0,4],[3,8]]
  //  [[1,5],[6,10],[2,3],[8,9]]
  //  [[1,4],[7,10],[3,5],[6,8]]
  //  [[2,4],[7,9],[5,6]]
  //  [[3,4],[7,8]]
  #define SORT_NETWORK_11(TYPE, CMP, begin)                                      \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[8]);                              \
    } while (0)
  
  //  39 comparators, parallel operations
  //  o--^-----^-----------------^--------^--------------------o
  //     |     |                 |        |
  //  o--v--^--|--^--^--------^--|--------|--^-----------------o
  //        |  |  |  |        |  |        |  |
  //  o--^--|--v--v--|-----^--|--|--------|--|-----^--^--------o
  //     |  |        |     |  |  |        |  |     |  |
  //  o--v--v--------|-----|--|--|--^-----|--|--^--v--|--^--^--o
  //                 |     |  |  |  |     |  |  |     |  |  |
  //  o--^-----^-----|-----|--|--v--|--^--v--v--|-----v--|--v--o
  //     |     |     |     |  |     |  |        |        |
  //  o--v--^--|--^--v--^--|--v-----|--|--------|--------v--^--o
  //        |  |  |     |  |        |  |        |           |
  //  o--^--|--v--v--^--|--v--^-----|--|--------|--------^--v--o
  //     |  |        |  |     |     |  |        |        |
  //  o--v--v--------|--|-----|--^--v--|--^--^--|-----^--|--^--o
  //                 |  |     |  |     |  |  |  |     |  |  |
  //  o--^-----^-----|--|-----|--|-----v--|--|--v--^--|--v--v--o
  //     |     |     |  |     |  |        |  |     |  |
  //  o--v--^--|--^--|--v-----|--|--------|--|-----v--v--------o
  //        |  |  |  |        |  |        |  |
  //  o--^--|--v--v--v--------v--|--------|--v-----------------o
  //     |  |                    |        |
  //  o--v--v--------------------v--------v--------------------o
  //
  //  [[0,1],[2,3],[4,5],[6,7],[8,9],[10,11]]
  //  [[1,3],[5,7],[9,11],[0,2],[4,6],[8,10]]
  //  [[1,2],[5,6],[9,10],[0,4],[7,11]]
  //  [[1,5],[6,10],[3,7],[4,8]]
  //  [[5,9],[2,6],[0,4],[7,11],[3,8]]
  //  [[1,5],[6,10],[2,3],[8,9]]
  //  [[1,4],[7,10],[3,5],[6,8]]
  //  [[2,4],[7,9],[5,6]]
  //  [[3,4],[7,8]]
  #define SORT_NETWORK_12(TYPE, CMP, begin)                                      \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[11]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[8]);                              \
    } while (0)
  
  //  45 comparators, 10 parallel operations
  //  o--------^--^-----^-----------------------------^-----------------o
  //           |  |     |                             |
  //  o--^-----|--v-----|-----^--------------^-----^--|-----^-----------o
  //     |     |        |     |              |     |  |     |
  //  o--|-----|--^--^--v-----|--------------|--^--|--|--^--v--^--------o
  //     |     |  |  |        |              |  |  |  |  |     |
  //  o--|--^--|--|--v-----^--|--------^-----|--|--v--|--|--^--v-----^--o
  //     |  |  |  |        |  |        |     |  |     |  |  |        |
  //  o--|--v--|--|--^-----|--v-----^--v-----|--|--^--|--|--|--^--^--v--o
  //     |     |  |  |     |        |        |  |  |  |  |  |  |  |
  //  o--|--^--|--|--|--^--|--------|-----^--|--|--|--v--v--v--|--v--^--o
  //     |  |  |  |  |  |  |        |     |  |  |  |           |     |
  //  o--|--|--|--v--v--|--|--^-----|--^--v--|--v--|--^--------v--^--v--o
  //     |  |  |        |  |  |     |  |     |     |  |           |
  //  o--v--|--|-----^--|--v--|--^--|--|-----v-----v--|--^--------v-----o
  //        |  |     |  |     |  |  |  |              |  |
  //  o-----v--|--^--|--|-----|--v--|--|--^-----^-----v--v--^-----------o
  //           |  |  |  |     |     |  |  |     |           |
  //  o--^-----|--|--|--v-----|-----v--|--v--^--|--^--------v-----------o
  //     |     |  |  |        |        |     |  |  |
  //  o--|-----|--|--|--^-----|--------v--^--|--v--v--------------------o
  //     |     |  |  |  |     |           |  |
  //  o--v-----|--v--|--v-----|--^--------v--v--------------------------o
  //           |     |        |  |
  //  o--------v-----v--------v--v--------------------------------------o
  //
  //  [[1,7],[9,11],[3,4],[5,8],[0,12],[2,6]]
  //  [[0,1],[2,3],[4,6],[8,11],[7,12],[5,9]]
  //  [[0,2],[3,7],[10,11],[1,4],[6,12]]
  //  [[7,8],[11,12],[4,9],[6,10]]
  //  [[3,4],[5,6],[8,9],[10,11],[1,7]]
  //  [[2,6],[9,11],[1,3],[4,7],[8,10],[0,5]]
  //  [[2,5],[6,8],[9,10]]
  //  [[1,2],[3,5],[7,8],[4,6]]
  //  [[2,3],[4,5],[6,7],[8,9]]
  //  [[3,4],[5,6]]
  #define SORT_NETWORK_13(TYPE, CMP, begin)                                      \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[11]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[11], begin[12]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[11]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
    } while (0)
  
  /* *INDENT-OFF* */
  /* clang-format off */
  
  //  51 comparators, 10 parallel operations
  //  o--^--^-----^-----------^-----------------------------------------------------------o
  //     |  |     |           |
  //  o--v--|--^--|--^--------|--^-----^-----------------------^--------------------------o
  //        |  |  |  |        |  |     |                       |
  //  o--^--v--|--|--|--^-----|--|--^--v-----------------------|--^--^--------------------o
  //     |     |  |  |  |     |  |  |                          |  |  |
  //  o--v-----v--|--|--|--^--|--|--|--^--------------^--------|--|--|--^--^--^-----------o
  //              |  |  |  |  |  |  |  |              |        |  |  |  |  |  |
  //  o--^--^-----v--|--|--|--|--|--|--|--^-----------|-----^--v--|--v--|--|--v-----------o
  //     |  |        |  |  |  |  |  |  |  |           |     |     |     |  |
  //  o--v--|--^-----v--|--|--|--|--|--|--|--^--^-----|-----|-----|--^--|--v-----^--------o
  //        |  |        |  |  |  |  |  |  |  |  |     |     |     |  |  |        |
  //  o--^--v--|--------v--|--|--|--|--|--|--|--|--^--|-----|-----|--v--|-----^--v-----^--o
  //     |     |           |  |  |  |  |  |  |  |  |  |     |     |     |     |        |
  //  o--v-----v-----------v--|--|--|--|--|--|--|--|--|--^--|--^--|-----|--^--|--^--^--v--o
  //                          |  |  |  |  |  |  |  |  |  |  |  |  |     |  |  |  |  |
  //  o--^--^-----^-----------v--|--|--|--|--|--|--|--|--|--v--|--v-----v--|--v--|--v--^--o
  //     |  |     |              |  |  |  |  |  |  |  |  |     |           |     |     |
  //  o--v--|--^--|--^-----------v--|--|--|--|--|--v--|--|-----|--^--------|-----v--^--v--o
  //        |  |  |  |              |  |  |  |  |     |  |     |  |        |        |
  //  o--^--v--|--|--|--------------v--|--|--|--v-----|--|-----|--v--------|--^-----v-----o
  //     |     |  |  |                 |  |  |        |  |     |           |  |
  //  o--v-----v--|--|-----------------v--|--|--------|--v-----|--^--------|--|--^--------o
  //              |  |                    |  |        |        |  |        |  |  |
  //  o--^--------v--|--------------------v--|--------v--------|--|--------v--v--v--------o
  //     |           |                       |                 |  |
  //  o--v-----------v-----------------------v-----------------v--v-----------------------o
  //
  //  [[0,1],[2,3],[4,5],[6,7],[8,9],[10,11],[12,13]]
  //  [[0,2],[4,6],[8,10],[1,3],[5,7],[9,11]]
  //  [[0,4],[8,12],[1,5],[9,13],[2,6],[3,7]]
  //  [[0,8],[1,9],[2,10],[3,11],[4,12],[5,13]]
  //  [[5,10],[6,9],[3,12],[7,11],[1,2],[4,8]]
  //  [[1,4],[7,13],[2,8],[5,6],[9,10]]
  //  [[2,4],[11,13],[3,8],[7,12]]
  //  [[6,8],[10,12],[3,5],[7,9]]
  //  [[3,4],[5,6],[7,8],[9,10],[11,12]]
  //  [[6,7],[8,9]]
  
  /* *INDENT-ON* */
  /* clang-format on */
  
  #define SORT_NETWORK_14(TYPE, CMP, begin)                                      \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[11]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[12], begin[13]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[13]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[13]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[13]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[11], begin[13]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[12]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[11], begin[12]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
    } while (0)
  
  /* *INDENT-OFF* */
  /* clang-format off */
  
  //  56 comparators, 10 parallel operations
  //  o--^--^-----^-----------^--------------------------------------------------------------o
  //     |  |     |           |
  //  o--v--|--^--|--^--------|--^-----^--------------------------^--------------------------o
  //        |  |  |  |        |  |     |                          |
  //  o--^--v--|--|--|--^-----|--|--^--v--------------------------|--^--^--------------------o
  //     |     |  |  |  |     |  |  |                             |  |  |
  //  o--v-----v--|--|--|--^--|--|--|--^-----------------^--------|--|--|--^--^--^-----------o
  //              |  |  |  |  |  |  |  |                 |        |  |  |  |  |  |
  //  o--^--^-----v--|--|--|--|--|--|--|--^--------------|-----^--v--|--v--|--|--v-----------o
  //     |  |        |  |  |  |  |  |  |  |              |     |     |     |  |
  //  o--v--|--^-----v--|--|--|--|--|--|--|--^-----^-----|-----|-----|--^--|--v-----^--------o
  //        |  |        |  |  |  |  |  |  |  |     |     |     |     |  |  |        |
  //  o--^--v--|--------v--|--|--|--|--|--|--|--^--|--^--|-----|-----|--v--|-----^--v-----^--o
  //     |     |           |  |  |  |  |  |  |  |  |  |  |     |     |     |     |        |
  //  o--v-----v-----------v--|--|--|--|--|--|--|--|--|--|--^--|--^--|-----|--^--|--^--^--v--o
  //                          |  |  |  |  |  |  |  |  |  |  |  |  |  |     |  |  |  |  |
  //  o--^--^-----^-----------v--|--|--|--|--|--|--|--|--|--|--v--|--v-----v--|--v--|--v--^--o
  //     |  |     |              |  |  |  |  |  |  |  |  |  |     |           |     |     |
  //  o--v--|--^--|--^-----------v--|--|--|--|--|--|--v--|--|-----|--^--------|-----v--^--v--o
  //        |  |  |  |              |  |  |  |  |  |     |  |     |  |        |        |
  //  o--^--v--|--|--|--^-----------v--|--|--|--|--v-----|--|-----|--v--------|--^-----v-----o
  //     |     |  |  |  |              |  |  |  |        |  |     |           |  |
  //  o--v-----v--|--|--|--------------v--|--|--|--------|--v-----|--^--^-----|--|--^--------o
  //              |  |  |                 |  |  |        |        |  |  |     |  |  |
  //  o--^--^-----v--|--|-----------------v--|--|--------v--------|--|--|-----v--v--v--------o
  //     |  |        |  |                    |  |                 |  |  |
  //  o--v--|--------v--|--------------------v--|--^--------------v--|--v--------------------o
  //        |           |                       |  |                 |
  //  o-----v-----------v-----------------------v--v-----------------v-----------------------o
  //
  //  [[0,1],[2,3],[4,5],[6,7],[8,9],[10,11],[12,13]]
  //  [[0,2],[4,6],[8,10],[12,14],[1,3],[5,7],[9,11]]
  //  [[0,4],[8,12],[1,5],[9,13],[2,6],[10,14],[3,7]]
  //  [[0,8],[1,9],[2,10],[3,11],[4,12],[5,13],[6,14]]
  //  [[5,10],[6,9],[3,12],[13,14],[7,11],[1,2],[4,8]]
  //  [[1,4],[7,13],[2,8],[11,14],[5,6],[9,10]]
  //  [[2,4],[11,13],[3,8],[7,12]]
  //  [[6,8],[10,12],[3,5],[7,9]]
  //  [[3,4],[5,6],[7,8],[9,10],[11,12]]
  //  [[6,7],[8,9]]
  
  /* *INDENT-ON* */
  /* clang-format on */
  
  #define SORT_NETWORK_15(TYPE, CMP, begin)                                      \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[11]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[12], begin[13]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[12], begin[14]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[13]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[14]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[13]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[14]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[13], begin[14]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[13]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[11], begin[14]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[11], begin[13]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[12]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[11], begin[12]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
    } while (0)
  
  /* *INDENT-OFF* */
  /* clang-format off */
  
  //  60 comparators, 10 parallel operations
  //  o--^--^-----^-----------^-----------------------------------------------------------------o
  //     |  |     |           |
  //  o--v--|--^--|--^--------|--^-----^-----------------------------^--------------------------o
  //        |  |  |  |        |  |     |                             |
  //  o--^--v--|--|--|--^-----|--|--^--v-----------------------------|--^--^--------------------o
  //     |     |  |  |  |     |  |  |                                |  |  |
  //  o--v-----v--|--|--|--^--|--|--|--^--------------------^--------|--|--|--^--^--^-----------o
  //              |  |  |  |  |  |  |  |                    |        |  |  |  |  |  |
  //  o--^--^-----v--|--|--|--|--|--|--|--^-----------------|-----^--v--|--v--|--|--v-----------o
  //     |  |        |  |  |  |  |  |  |  |                 |     |     |     |  |
  //  o--v--|--^-----v--|--|--|--|--|--|--|--^--------^-----|-----|-----|--^--|--v-----^--------o
  //        |  |        |  |  |  |  |  |  |  |        |     |     |     |  |  |        |
  //  o--^--v--|--------v--|--|--|--|--|--|--|--^-----|--^--|-----|-----|--v--|-----^--v-----^--o
  //     |     |           |  |  |  |  |  |  |  |     |  |  |     |     |     |     |        |
  //  o--v-----v-----------v--|--|--|--|--|--|--|--^--|--|--|--^--|--^--|-----|--^--|--^--^--v--o
  //                          |  |  |  |  |  |  |  |  |  |  |  |  |  |  |     |  |  |  |  |
  //  o--^--^-----^-----------v--|--|--|--|--|--|--|--|--|--|--|--v--|--v-----v--|--v--|--v--^--o
  //     |  |     |              |  |  |  |  |  |  |  |  |  |  |     |           |     |     |
  //  o--v--|--^--|--^-----------v--|--|--|--|--|--|--|--v--|--|-----|--^--------|-----v--^--v--o
  //        |  |  |  |              |  |  |  |  |  |  |     |  |     |  |        |        |
  //  o--^--v--|--|--|--^-----------v--|--|--|--|--|--v-----|--|-----|--v--------|--^-----v-----o
  //     |     |  |  |  |              |  |  |  |  |        |  |     |           |  |
  //  o--v-----v--|--|--|--^-----------v--|--|--|--|--------|--v-----|--^--^-----|--|--^--------o
  //              |  |  |  |              |  |  |  |        |        |  |  |     |  |  |
  //  o--^--^-----v--|--|--|--------------v--|--|--|--------v--------|--|--|-----v--v--v--------o
  //     |  |        |  |  |                 |  |  |                 |  |  |
  //  o--v--|--^-----v--|--|-----------------v--|--|--^--------------v--|--v--------------------o
  //        |  |        |  |                    |  |  |                 |
  //  o--^--v--|--------v--|--------------------v--|--v-----------------v-----------------------o
  //     |     |           |                       |
  //  o--v-----v-----------v-----------------------v--------------------------------------------o
  //
  //  [[0,1],[2,3],[4,5],[6,7],[8,9],[10,11],[12,13],[14,15]]
  //  [[0,2],[4,6],[8,10],[12,14],[1,3],[5,7],[9,11],[13,15]]
  //  [[0,4],[8,12],[1,5],[9,13],[2,6],[10,14],[3,7],[11,15]]
  //  [[0,8],[1,9],[2,10],[3,11],[4,12],[5,13],[6,14],[7,15]]
  //  [[5,10],[6,9],[3,12],[13,14],[7,11],[1,2],[4,8]]
  //  [[1,4],[7,13],[2,8],[11,14],[5,6],[9,10]]
  //  [[2,4],[11,13],[3,8],[7,12]]
  //  [[6,8],[10,12],[3,5],[7,9]]
  //  [[3,4],[5,6],[7,8],[9,10],[11,12]]
  //  [[6,7],[8,9]]
  
  /* *INDENT-ON* */
  /* clang-format on */
  
  #define SORT_NETWORK_16(TYPE, CMP, begin)                                      \
    do {                                                                         \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[11]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[12], begin[13]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[14], begin[15]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[12], begin[14]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[3]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[13], begin[15]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[13]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[14]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[11], begin[15]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[13]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[14]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[15]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[13], begin[14]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[11]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[2]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[4], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[1], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[13]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[11], begin[14]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[2], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[11], begin[13]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[12]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[10], begin[12]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[5]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[9]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[3], begin[4]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[5], begin[6]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[7], begin[8]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[9], begin[10]);                             \
      SORT_CMP_SWAP(TYPE, CMP, begin[11], begin[12]);                            \
      SORT_CMP_SWAP(TYPE, CMP, begin[6], begin[7]);                              \
      SORT_CMP_SWAP(TYPE, CMP, begin[8], begin[9]);                              \
    } while (0)
  
  #define SORT_INNER(TYPE, CMP, begin, end, len)                                 \
    switch (len) {                                                               \
    default:                                                                     \
      __unreachable();                                                           \
    case 0:                                                                      \
    case 1:                                                                      \
      break;                                                                     \
    case 2:                                                                      \
      SORT_CMP_SWAP(TYPE, CMP, begin[0], begin[1]);                              \
      break;                                                                     \
    case 3:                                                                      \
      SORT_NETWORK_3(TYPE, CMP, begin);                                          \
      break;                                                                     \
    case 4:                                                                      \
      SORT_NETWORK_4(TYPE, CMP, begin);                                          \
      break;                                                                     \
    case 5:                                                                      \
      SORT_NETWORK_5(TYPE, CMP, begin);                                          \
      break;                                                                     \
    case 6:                                                                      \
      SORT_NETWORK_6(TYPE, CMP, begin);                                          \
      break;                                                                     \
    case 7:                                                                      \
      SORT_NETWORK_7(TYPE, CMP, begin);                                          \
      break;                                                                     \
    case 8:                                                                      \
      SORT_NETWORK_8(TYPE, CMP, begin);                                          \
      break;                                                                     \
    case 9:                                                                      \
      SORT_NETWORK_9(TYPE, CMP, begin);                                          \
      break;                                                                     \
    case 10:                                                                     \
      SORT_NETWORK_10(TYPE, CMP, begin);                                         \
      break;                                                                     \
    case 11:                                                                     \
      SORT_NETWORK_11(TYPE, CMP, begin);                                         \
      break;                                                                     \
    case 12:                                                                     \
      SORT_NETWORK_12(TYPE, CMP, begin);                                         \
      break;                                                                     \
    case 13:                                                                     \
      SORT_NETWORK_13(TYPE, CMP, begin);                                         \
      break;                                                                     \
    case 14:                                                                     \
      SORT_NETWORK_14(TYPE, CMP, begin);                                         \
      break;                                                                     \
    case 15:                                                                     \
      SORT_NETWORK_15(TYPE, CMP, begin);                                         \
      break;                                                                     \
    case 16:                                                                     \
      SORT_NETWORK_16(TYPE, CMP, begin);                                         \
      break;                                                                     \
    }
  
  #define SORT_SWAP(TYPE, a, b)                                                  \
    do {                                                                         \
      const TYPE swap_tmp = (a);                                                 \
      (a) = (b);                                                                 \
      (b) = swap_tmp;                                                            \
    } while (0)
  
  #define SORT_PUSH(low, high)                                                   \
    do {                                                                         \
      top->lo = (low);                                                           \
      top->hi = (high);                                                          \
      ++top;                                                                     \
    } while (0)
  
  #define SORT_POP(low, high)                                                    \
    do {                                                                         \
      --top;                                                                     \
      low = top->lo;                                                             \
      high = top->hi;                                                            \
    } while (0)
  
  #define SORT_IMPL(NAME, EXPECT_LOW_CARDINALITY_OR_PRESORTED, TYPE, CMP)        \
                                                                                 \
    static __inline bool NAME##_is_sorted(const TYPE *first, const TYPE *last) { \
      while (++first <= last)                                                    \
        if (CMP(first[0], first[-1]))                                            \
          return false;                                                          \
      return true;                                                               \
    }                                                                            \
                                                                                 \
    typedef struct {                                                             \
      TYPE *lo, *hi;                                                             \
    } NAME##_stack;                                                              \
                                                                                 \
    static __hot void NAME(TYPE *const begin, TYPE *const end) {                 \
      NAME##_stack stack[sizeof(unsigned) * CHAR_BIT], *top = stack;             \
                                                                                 \
      TYPE *hi = end - 1;                                                        \
      TYPE *lo = begin;                                                          \
      while (true) {                                                             \
        const ptrdiff_t len = hi - lo;                                           \
        if (len < 16) {                                                          \
          SORT_INNER(TYPE, CMP, lo, hi + 1, len + 1);                            \
          if (unlikely(top == stack))                                            \
            break;                                                               \
          SORT_POP(lo, hi);                                                      \
          continue;                                                              \
        }                                                                        \
                                                                                 \
        TYPE *mid = lo + (len >> 1);                                             \
        SORT_CMP_SWAP(TYPE, CMP, *lo, *mid);                                     \
        SORT_CMP_SWAP(TYPE, CMP, *mid, *hi);                                     \
        SORT_CMP_SWAP(TYPE, CMP, *lo, *mid);                                     \
                                                                                 \
        TYPE *right = hi - 1;                                                    \
        TYPE *left = lo + 1;                                                     \
        while (1) {                                                              \
          while (CMP(*left, *mid))                                               \
            ++left;                                                              \
          while (CMP(*mid, *right))                                              \
            --right;                                                             \
          if (unlikely(left > right)) {                                          \
            if (EXPECT_LOW_CARDINALITY_OR_PRESORTED) {                           \
              if (NAME##_is_sorted(lo, right))                                   \
                lo = right + 1;                                                  \
              if (NAME##_is_sorted(left, hi))                                    \
                hi = left;                                                       \
            }                                                                    \
            break;                                                               \
          }                                                                      \
          SORT_SWAP(TYPE, *left, *right);                                        \
          mid = (mid == left) ? right : (mid == right) ? left : mid;             \
          ++left;                                                                \
          --right;                                                               \
        }                                                                        \
                                                                                 \
        if (right - lo > hi - left) {                                            \
          SORT_PUSH(lo, right);                                                  \
          lo = left;                                                             \
        } else {                                                                 \
          SORT_PUSH(left, hi);                                                   \
          hi = right;                                                            \
        }                                                                        \
      }                                                                          \
                                                                                 \
      if (mdbx_audit_enabled()) {                                                \
        for (TYPE *scan = begin + 1; scan < end; ++scan)                         \
          assert(CMP(scan[-1], scan[0]));                                        \
      }                                                                          \
    }
  
  /*------------------------------------------------------------------------------
   * LY: Binary search */
  
  #define SEARCH_IMPL(NAME, TYPE_LIST, TYPE_ARG, CMP)                            \
    static __always_inline TYPE_LIST *NAME(TYPE_LIST *first, unsigned length,    \
                                           const TYPE_ARG item) {                \
      TYPE_LIST *const begin = first, *const end = begin + length;               \
                                                                                 \
      while (length > 3) {                                                       \
        const unsigned whole = length;                                           \
        length >>= 1;                                                            \
        TYPE_LIST *const middle = first + length;                                \
        if (CMP(*middle, item)) {                                                \
          first = middle + 1;                                                    \
          length = whole - length - 1;                                           \
        }                                                                        \
      }                                                                          \
                                                                                 \
      switch (length) {                                                          \
      case 3:                                                                    \
        if (!CMP(*first, item))                                                  \
          break;                                                                 \
        ++first;                                                                 \
        __fallthrough /* fall through */;                                        \
      case 2:                                                                    \
        if (!CMP(*first, item))                                                  \
          break;                                                                 \
        ++first;                                                                 \
        __fallthrough /* fall through */;                                        \
      case 1:                                                                    \
        if (!CMP(*first, item))                                                  \
          break;                                                                 \
        ++first;                                                                 \
        __fallthrough /* fall through */;                                        \
      case 0:                                                                    \
        break;                                                                   \
      default:                                                                   \
        __unreachable();                                                         \
      }                                                                          \
                                                                                 \
      if (mdbx_audit_enabled()) {                                                \
        for (TYPE_LIST *scan = begin; scan < first; ++scan)                      \
          assert(CMP(*scan, item));                                              \
        for (TYPE_LIST *scan = first; scan < end; ++scan)                        \
          assert(!CMP(*scan, item));                                             \
        (void)begin, (void)end;                                                  \
      }                                                                          \
                                                                                 \
      return first;                                                              \
    }
  
  /*----------------------------------------------------------------------------*/
  
  static __always_inline size_t pnl2bytes(const size_t size) {
    assert(size > 0 && size <= MDBX_PNL_MAX * 2);
    size_t bytes =
        ceil_powerof2(MDBX_ASSUME_MALLOC_OVERHEAD + sizeof(pgno_t) * (size + 2),
                      MDBX_PNL_GRANULATE * sizeof(pgno_t)) -
        MDBX_ASSUME_MALLOC_OVERHEAD;
    return bytes;
  }
  
  static __always_inline pgno_t bytes2pnl(const size_t bytes) {
    size_t size = bytes / sizeof(pgno_t);
    assert(size > 2 && size <= MDBX_PNL_MAX * 2);
    return (pgno_t)size - 2;
  }
  
  static MDBX_PNL mdbx_pnl_alloc(size_t size) {
    size_t bytes = pnl2bytes(size);
    MDBX_PNL pl = mdbx_malloc(bytes);
    if (likely(pl)) {
  #if __GLIBC_PREREQ(2, 12) || defined(__FreeBSD__) || defined(malloc_usable_size)
      bytes = malloc_usable_size(pl);
  #endif /* malloc_usable_size */
      pl[0] = bytes2pnl(bytes);
      assert(pl[0] >= size);
      pl[1] = 0;
      pl += 1;
    }
    return pl;
  }
  
  static void mdbx_pnl_free(MDBX_PNL pl) {
    if (likely(pl))
      mdbx_free(pl - 1);
  }
  
  /* Shrink the PNL to the default size if it has grown larger */
  static void mdbx_pnl_shrink(MDBX_PNL *ppl) {
    assert(bytes2pnl(pnl2bytes(MDBX_PNL_INITIAL)) == MDBX_PNL_INITIAL);
    assert(MDBX_PNL_SIZE(*ppl) <= MDBX_PNL_MAX &&
           MDBX_PNL_ALLOCLEN(*ppl) >= MDBX_PNL_SIZE(*ppl));
    MDBX_PNL_SIZE(*ppl) = 0;
    if (unlikely(MDBX_PNL_ALLOCLEN(*ppl) >
                 MDBX_PNL_INITIAL * 2 - MDBX_CACHELINE_SIZE / sizeof(pgno_t))) {
      size_t bytes = pnl2bytes(MDBX_PNL_INITIAL);
      MDBX_PNL pl = mdbx_realloc(*ppl - 1, bytes);
      if (likely(pl)) {
  #if __GLIBC_PREREQ(2, 12) || defined(__FreeBSD__) || defined(malloc_usable_size)
        bytes = malloc_usable_size(pl);
  #endif /* malloc_usable_size */
        *pl = bytes2pnl(bytes);
        *ppl = pl + 1;
      }
    }
  }
  
  /* Grow the PNL to the size growed to at least given size */
  static int mdbx_pnl_reserve(MDBX_PNL *ppl, const size_t wanna) {
    const size_t allocated = MDBX_PNL_ALLOCLEN(*ppl);
    assert(MDBX_PNL_SIZE(*ppl) <= MDBX_PNL_MAX &&
           MDBX_PNL_ALLOCLEN(*ppl) >= MDBX_PNL_SIZE(*ppl));
    if (likely(allocated >= wanna))
      return MDBX_SUCCESS;
  
    if (unlikely(wanna > /* paranoia */ MDBX_PNL_MAX))
      return MDBX_TXN_FULL;
  
    const size_t size = (wanna + wanna - allocated < MDBX_PNL_MAX)
                            ? wanna + wanna - allocated
                            : MDBX_PNL_MAX;
    size_t bytes = pnl2bytes(size);
    MDBX_PNL pl = mdbx_realloc(*ppl - 1, bytes);
    if (likely(pl)) {
  #if __GLIBC_PREREQ(2, 12) || defined(__FreeBSD__) || defined(malloc_usable_size)
      bytes = malloc_usable_size(pl);
  #endif /* malloc_usable_size */
      *pl = bytes2pnl(bytes);
      assert(*pl >= wanna);
      *ppl = pl + 1;
      return MDBX_SUCCESS;
    }
    return MDBX_ENOMEM;
  }
  
  /* Make room for num additional elements in an PNL */
  static __always_inline int __must_check_result mdbx_pnl_need(MDBX_PNL *ppl,
                                                               size_t num) {
    assert(MDBX_PNL_SIZE(*ppl) <= MDBX_PNL_MAX &&
           MDBX_PNL_ALLOCLEN(*ppl) >= MDBX_PNL_SIZE(*ppl));
    assert(num <= MDBX_PNL_MAX);
    const size_t wanna = MDBX_PNL_SIZE(*ppl) + num;
    return likely(MDBX_PNL_ALLOCLEN(*ppl) >= wanna)
               ? MDBX_SUCCESS
               : mdbx_pnl_reserve(ppl, wanna);
  }
  
  static __always_inline void mdbx_pnl_xappend(MDBX_PNL pl, pgno_t pgno) {
    assert(MDBX_PNL_SIZE(pl) < MDBX_PNL_ALLOCLEN(pl));
    if (mdbx_audit_enabled()) {
      for (unsigned i = MDBX_PNL_SIZE(pl); i > 0; --i)
        assert(pgno != pl[i]);
    }
    MDBX_PNL_SIZE(pl) += 1;
    MDBX_PNL_LAST(pl) = pgno;
  }
  
  /* Append an pgno onto an unsorted PNL */
  static __hot int __must_check_result mdbx_pnl_append(MDBX_PNL *ppl,
                                                       pgno_t pgno) {
    /* Too big? */
    if (unlikely(MDBX_PNL_SIZE(*ppl) == MDBX_PNL_ALLOCLEN(*ppl))) {
      int rc = mdbx_pnl_need(ppl, MDBX_PNL_GRANULATE);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
    mdbx_pnl_xappend(*ppl, pgno);
    return MDBX_SUCCESS;
  }
  
  /* Append an PNL onto an unsorted PNL */
  static int __must_check_result mdbx_pnl_append_list(MDBX_PNL *ppl,
                                                      MDBX_PNL append) {
    const unsigned len = MDBX_PNL_SIZE(append);
    if (likely(len)) {
      int rc = mdbx_pnl_need(ppl, MDBX_PNL_SIZE(append));
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
  
      const MDBX_PNL pnl = *ppl;
      unsigned w = MDBX_PNL_SIZE(pnl), r = 1;
      do
        pnl[++w] = append[r];
      while (++r <= len);
      MDBX_PNL_SIZE(pnl) = w;
    }
    return MDBX_SUCCESS;
  }
  
  /* Append an pgno range onto an unsorted PNL */
  static __hot int __must_check_result mdbx_pnl_append_range(MDBX_PNL *ppl,
                                                             pgno_t pgno,
                                                             unsigned n) {
    assert(n > 0);
    int rc = mdbx_pnl_need(ppl, n);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    const MDBX_PNL pnl = *ppl;
  #if MDBX_PNL_ASCENDING
    unsigned w = MDBX_PNL_SIZE(pnl);
    do
      pnl[++w] = pgno++;
    while (--n);
    MDBX_PNL_SIZE(pnl) = w;
  #else
    unsigned w = MDBX_PNL_SIZE(pnl) + n;
    MDBX_PNL_SIZE(pnl) = w;
    do
      pnl[w--] = --n + pgno;
    while (n);
  #endif
  
    return MDBX_SUCCESS;
  }
  
  /* Append an pgno range into the sorted PNL */
  static __hot int __must_check_result mdbx_pnl_insert_range(MDBX_PNL *ppl,
                                                             pgno_t pgno,
                                                             unsigned n) {
    assert(n > 0);
    int rc = mdbx_pnl_need(ppl, n);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    const MDBX_PNL pnl = *ppl;
    unsigned r = MDBX_PNL_SIZE(pnl), w = r + n;
    MDBX_PNL_SIZE(pnl) = w;
    while (r && MDBX_PNL_DISORDERED(pnl[r], pgno))
      pnl[w--] = pnl[r--];
  
    for (pgno_t fill = MDBX_PNL_ASCENDING ? pgno + n : pgno; w > r; --w)
      pnl[w] = MDBX_PNL_ASCENDING ? --fill : fill++;
  
    return MDBX_SUCCESS;
  }
  
  static bool mdbx_pnl_check(const MDBX_PNL pl, const pgno_t limit) {
    assert(limit >= MIN_PAGENO && limit <= MAX_PAGENO + 1);
    if (likely(MDBX_PNL_SIZE(pl))) {
      assert(MDBX_PNL_LEAST(pl) >= MIN_PAGENO);
      assert(MDBX_PNL_MOST(pl) < limit);
      assert(MDBX_PNL_SIZE(pl) <= MDBX_PNL_MAX);
      if (unlikely(MDBX_PNL_SIZE(pl) > MDBX_PNL_MAX * 3 / 2))
        return false;
      if (unlikely(MDBX_PNL_LEAST(pl) < MIN_PAGENO))
        return false;
      if (unlikely(MDBX_PNL_MOST(pl) >= limit))
        return false;
      if (mdbx_audit_enabled()) {
        for (const pgno_t *scan = &MDBX_PNL_LAST(pl); --scan > pl;) {
          assert(MDBX_PNL_ORDERED(scan[0], scan[1]));
          if (unlikely(!MDBX_PNL_ORDERED(scan[0], scan[1])))
            return false;
        }
      }
    }
    return true;
  }
  
  static __always_inline bool mdbx_pnl_check4assert(const MDBX_PNL pl,
                                                    const pgno_t limit) {
    if (unlikely(pl == nullptr))
      return true;
    assert(MDBX_PNL_ALLOCLEN(pl) >= MDBX_PNL_SIZE(pl));
    if (unlikely(MDBX_PNL_ALLOCLEN(pl) < MDBX_PNL_SIZE(pl)))
      return false;
    return mdbx_pnl_check(pl, limit);
  }
  
  /* Merge an PNL onto an PNL. The destination PNL must be big enough */
  static void __hot mdbx_pnl_xmerge(MDBX_PNL dst, const MDBX_PNL src) {
    assert(mdbx_pnl_check4assert(dst, MAX_PAGENO + 1));
    assert(mdbx_pnl_check(src, MAX_PAGENO + 1));
    const size_t total = MDBX_PNL_SIZE(dst) + MDBX_PNL_SIZE(src);
    assert(MDBX_PNL_ALLOCLEN(dst) >= total);
    pgno_t *w = dst + total;
    pgno_t *d = dst + MDBX_PNL_SIZE(dst);
    const pgno_t *s = src + MDBX_PNL_SIZE(src);
    dst[0] = /* detent for scan below */ (MDBX_PNL_ASCENDING ? 0 : ~(pgno_t)0);
    while (s > src) {
      while (MDBX_PNL_ORDERED(*s, *d))
        *w-- = *d--;
      *w-- = *s--;
    }
    MDBX_PNL_SIZE(dst) = (pgno_t)total;
    assert(mdbx_pnl_check4assert(dst, MAX_PAGENO + 1));
  }
  
  SORT_IMPL(pgno_sort, false, pgno_t, MDBX_PNL_ORDERED)
  static __hot void mdbx_pnl_sort(MDBX_PNL pnl) {
    pgno_sort(MDBX_PNL_BEGIN(pnl), MDBX_PNL_END(pnl));
    assert(mdbx_pnl_check(pnl, MAX_PAGENO + 1));
  }
  
  /* Search for an pgno in an PNL.
   * Returns The index of the first item greater than or equal to pgno. */
  SEARCH_IMPL(pgno_bsearch, pgno_t, pgno_t, MDBX_PNL_ORDERED)
  
  static __hot unsigned mdbx_pnl_search(MDBX_PNL pnl, pgno_t id) {
    assert(mdbx_pnl_check4assert(pnl, MAX_PAGENO + 1));
    pgno_t *begin = MDBX_PNL_BEGIN(pnl);
    pgno_t *it = pgno_bsearch(begin, MDBX_PNL_SIZE(pnl), id);
    pgno_t *end = begin + MDBX_PNL_SIZE(pnl);
    assert(it >= begin && it <= end);
    if (it != begin)
      assert(MDBX_PNL_ORDERED(it[-1], id));
    if (it != end)
      assert(!MDBX_PNL_ORDERED(it[0], id));
    return (unsigned)(it - begin + 1);
  }
  
  static __hot unsigned mdbx_pnl_exist(MDBX_PNL pnl, pgno_t id) {
    unsigned n = mdbx_pnl_search(pnl, id);
    return (n <= MDBX_PNL_SIZE(pnl) && pnl[n] == id) ? n : 0;
  }
  
  /*----------------------------------------------------------------------------*/
  
  static __always_inline size_t txl2bytes(const size_t size) {
    assert(size > 0 && size <= MDBX_TXL_MAX * 2);
    size_t bytes =
        ceil_powerof2(MDBX_ASSUME_MALLOC_OVERHEAD + sizeof(txnid_t) * (size + 2),
                      MDBX_TXL_GRANULATE * sizeof(txnid_t)) -
        MDBX_ASSUME_MALLOC_OVERHEAD;
    return bytes;
  }
  
  static __always_inline size_t bytes2txl(const size_t bytes) {
    size_t size = bytes / sizeof(txnid_t);
    assert(size > 2 && size <= MDBX_TXL_MAX * 2);
    return size - 2;
  }
  
  static MDBX_TXL mdbx_txl_alloc(void) {
    size_t bytes = txl2bytes(MDBX_TXL_INITIAL);
    MDBX_TXL tl = mdbx_malloc(bytes);
    if (likely(tl)) {
  #if __GLIBC_PREREQ(2, 12) || defined(__FreeBSD__) || defined(malloc_usable_size)
      bytes = malloc_usable_size(tl);
  #endif /* malloc_usable_size */
      tl[0] = bytes2txl(bytes);
      assert(tl[0] >= MDBX_TXL_INITIAL);
      tl[1] = 0;
      tl += 1;
    }
    return tl;
  }
  
  static void mdbx_txl_free(MDBX_TXL tl) {
    if (likely(tl))
      mdbx_free(tl - 1);
  }
  
  static int mdbx_txl_reserve(MDBX_TXL *ptl, const size_t wanna) {
    const size_t allocated = (size_t)MDBX_PNL_ALLOCLEN(*ptl);
    assert(MDBX_PNL_SIZE(*ptl) <= MDBX_TXL_MAX &&
           MDBX_PNL_ALLOCLEN(*ptl) >= MDBX_PNL_SIZE(*ptl));
    if (likely(allocated >= wanna))
      return MDBX_SUCCESS;
  
    if (unlikely(wanna > /* paranoia */ MDBX_TXL_MAX))
      return MDBX_TXN_FULL;
  
    const size_t size = (wanna + wanna - allocated < MDBX_TXL_MAX)
                            ? wanna + wanna - allocated
                            : MDBX_TXL_MAX;
    size_t bytes = txl2bytes(size);
    MDBX_TXL tl = mdbx_realloc(*ptl - 1, bytes);
    if (likely(tl)) {
  #if __GLIBC_PREREQ(2, 12) || defined(__FreeBSD__) || defined(malloc_usable_size)
      bytes = malloc_usable_size(tl);
  #endif /* malloc_usable_size */
      *tl = bytes2txl(bytes);
      assert(*tl >= wanna);
      *ptl = tl + 1;
      return MDBX_SUCCESS;
    }
    return MDBX_ENOMEM;
  }
  
  static __always_inline int __must_check_result mdbx_txl_need(MDBX_TXL *ptl,
                                                               size_t num) {
    assert(MDBX_PNL_SIZE(*ptl) <= MDBX_TXL_MAX &&
           MDBX_PNL_ALLOCLEN(*ptl) >= MDBX_PNL_SIZE(*ptl));
    assert(num <= MDBX_PNL_MAX);
    const size_t wanna = (size_t)MDBX_PNL_SIZE(*ptl) + num;
    return likely(MDBX_PNL_ALLOCLEN(*ptl) >= wanna)
               ? MDBX_SUCCESS
               : mdbx_txl_reserve(ptl, wanna);
  }
  
  static __always_inline void mdbx_txl_xappend(MDBX_TXL tl, txnid_t id) {
    assert(MDBX_PNL_SIZE(tl) < MDBX_PNL_ALLOCLEN(tl));
    MDBX_PNL_SIZE(tl) += 1;
    MDBX_PNL_LAST(tl) = id;
  }
  
  #define TXNID_SORT_CMP(first, last) ((first) > (last))
  SORT_IMPL(txnid_sort, false, txnid_t, TXNID_SORT_CMP)
  static void mdbx_txl_sort(MDBX_TXL tl) {
    txnid_sort(MDBX_PNL_BEGIN(tl), MDBX_PNL_END(tl));
  }
  
  static int __must_check_result mdbx_txl_append(MDBX_TXL *ptl, txnid_t id) {
    if (unlikely(MDBX_PNL_SIZE(*ptl) == MDBX_PNL_ALLOCLEN(*ptl))) {
      int rc = mdbx_txl_need(ptl, MDBX_TXL_GRANULATE);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
    mdbx_txl_xappend(*ptl, id);
    return MDBX_SUCCESS;
  }
  
  /*----------------------------------------------------------------------------*/
  
  #define DP_SORT_CMP(first, last) ((first).pgno < (last).pgno)
  SORT_IMPL(dp_sort, false, MDBX_DP, DP_SORT_CMP)
  static __always_inline MDBX_DPL mdbx_dpl_sort(MDBX_DPL dl) {
    assert(dl->length <= MDBX_DPL_TXNFULL);
    assert(dl->sorted <= dl->length);
    if (dl->sorted != dl->length) {
      dl->sorted = dl->length;
      dp_sort(dl + 1, dl + dl->length + 1);
    }
    return dl;
  }
  
  /* Returns the index of the first dirty-page whose pgno
   * member is greater than or equal to id. */
  #define DP_SEARCH_CMP(dp, id) ((dp).pgno < (id))
  SEARCH_IMPL(dp_bsearch, MDBX_DP, pgno_t, DP_SEARCH_CMP)
  
  static unsigned __hot mdbx_dpl_search(MDBX_DPL dl, pgno_t pgno) {
    if (mdbx_audit_enabled()) {
      for (const MDBX_DP *ptr = dl + dl->sorted; --ptr > dl;) {
        assert(ptr[0].pgno < ptr[1].pgno);
        assert(ptr[0].pgno >= NUM_METAS);
      }
    }
  
    switch (dl->length - dl->sorted) {
    default:
      /* sort a whole */
      dl->sorted = dl->length;
      dp_sort(dl + 1, dl + dl->length + 1);
      __fallthrough; /* fall through */
    case 0:
      /* whole sorted cases */
      if (mdbx_audit_enabled()) {
        for (const MDBX_DP *ptr = dl + dl->length; --ptr > dl;) {
          assert(ptr[0].pgno < ptr[1].pgno);
          assert(ptr[0].pgno >= NUM_METAS);
        }
      }
      return (unsigned)(dp_bsearch(dl + 1, dl->length, pgno) - dl);
  
  #define LINEAR_SEARCH_CASE(N)                                                  \
    case N:                                                                      \
      if (dl[dl->length - N + 1].pgno == pgno)                                   \
        return dl->length - N + 1;                                               \
      __fallthrough
  
      /* try linear search until the threshold */
      LINEAR_SEARCH_CASE(16); /* fall through */
      LINEAR_SEARCH_CASE(15); /* fall through */
      LINEAR_SEARCH_CASE(14); /* fall through */
      LINEAR_SEARCH_CASE(13); /* fall through */
      LINEAR_SEARCH_CASE(12); /* fall through */
      LINEAR_SEARCH_CASE(11); /* fall through */
      LINEAR_SEARCH_CASE(10); /* fall through */
      LINEAR_SEARCH_CASE(9);  /* fall through */
      LINEAR_SEARCH_CASE(8);  /* fall through */
      LINEAR_SEARCH_CASE(7);  /* fall through */
      LINEAR_SEARCH_CASE(6);  /* fall through */
      LINEAR_SEARCH_CASE(5);  /* fall through */
      LINEAR_SEARCH_CASE(4);  /* fall through */
      LINEAR_SEARCH_CASE(3);  /* fall through */
      LINEAR_SEARCH_CASE(2);  /* fall through */
    case 1:
      if (dl[dl->length].pgno == pgno)
        return dl->length;
      /* continue bsearch on the sorted part */
      return (unsigned)(dp_bsearch(dl + 1, dl->sorted, pgno) - dl);
    }
  }
  
  static __always_inline MDBX_page *mdbx_dpl_find(MDBX_DPL dl, pgno_t pgno) {
    const unsigned i = mdbx_dpl_search(dl, pgno);
    assert((int)i > 0);
    return (i <= dl->length && dl[i].pgno == pgno) ? dl[i].ptr : nullptr;
  }
  
  static __hot MDBX_page *mdbx_dpl_remove(MDBX_DPL dl, pgno_t prno) {
    unsigned i = mdbx_dpl_search(dl, prno);
    assert((int)i > 0);
    MDBX_page *mp = nullptr;
    if (i <= dl->length && dl[i].pgno == prno) {
      dl->sorted -= dl->sorted >= i;
      mp = dl[i].ptr;
      while (i < dl->length) {
        dl[i] = dl[i + 1];
        ++i;
      }
      dl->length -= 1;
    }
    return mp;
  }
  
  static __always_inline int __must_check_result
  mdbx_dpl_append(MDBX_DPL dl, pgno_t pgno, MDBX_page *page) {
    assert(dl->length <= MDBX_DPL_TXNFULL);
    if (mdbx_audit_enabled()) {
      for (unsigned i = dl->length; i > 0; --i) {
        assert(dl[i].pgno != pgno);
        if (unlikely(dl[i].pgno == pgno))
          return MDBX_PROBLEM;
      }
    }
  
    if (unlikely(dl->length == MDBX_DPL_TXNFULL))
      return MDBX_TXN_FULL;
  
    /* append page */
    const unsigned n = dl->length + 1;
    if (n == 1 || (dl->sorted >= dl->length && dl[n - 1].pgno < pgno))
      dl->sorted = n;
    dl->length = n;
    dl[n].pgno = pgno;
    dl[n].ptr = page;
    return MDBX_SUCCESS;
  }
  
  static __always_inline void mdbx_dpl_clear(MDBX_DPL dl) {
    dl->sorted = dl->length = 0;
  }
  
  /*----------------------------------------------------------------------------*/
  
  uint8_t mdbx_runtime_flags = MDBX_RUNTIME_FLAGS_INIT;
  uint8_t mdbx_loglevel = MDBX_LOG_FATAL;
  MDBX_debug_func *mdbx_debug_logger;
  
  static bool mdbx_refund(MDBX_txn *txn);
  static __must_check_result int mdbx_page_retire(MDBX_cursor *mc, MDBX_page *mp);
  static __must_check_result int mdbx_page_loose(MDBX_txn *txn, MDBX_page *mp);
  static int mdbx_page_alloc(MDBX_cursor *mc, const unsigned num,
                             MDBX_page **const mp, int flags);
  static txnid_t mdbx_kick_longlived_readers(MDBX_env *env,
                                             const txnid_t laggard);
  
  static int mdbx_page_new(MDBX_cursor *mc, uint32_t flags, unsigned num,
                           MDBX_page **mp);
  static int mdbx_page_touch(MDBX_cursor *mc);
  static int mdbx_cursor_touch(MDBX_cursor *mc);
  
  #define MDBX_END_NAMES                                                         \
    {                                                                            \
      "committed", "empty-commit", "abort", "reset", "reset-tmp", "fail-begin",  \
          "fail-beginchild"                                                      \
    }
  enum {
    /* mdbx_txn_end operation number, for logging */
    MDBX_END_COMMITTED,
    MDBX_END_EMPTY_COMMIT,
    MDBX_END_ABORT,
    MDBX_END_RESET,
    MDBX_END_RESET_TMP,
    MDBX_END_FAIL_BEGIN,
    MDBX_END_FAIL_BEGINCHILD
  };
  #define MDBX_END_OPMASK 0x0F  /* mask for mdbx_txn_end() operation number */
  #define MDBX_END_UPDATE 0x10  /* update env state (DBIs) */
  #define MDBX_END_FREE 0x20    /* free txn unless it is MDBX_env.me_txn0 */
  #define MDBX_END_EOTDONE 0x40 /* txn's cursors already closed */
  #define MDBX_END_SLOT 0x80    /* release any reader slot if MDBX_NOTLS */
  static int mdbx_txn_end(MDBX_txn *txn, unsigned mode);
  
  static int __must_check_result mdbx_page_get(MDBX_cursor *mc, pgno_t pgno,
                                               MDBX_page **mp, int *lvl,
                                               txnid_t pp_txnid);
  static int __must_check_result mdbx_page_search_root(MDBX_cursor *mc,
                                                       const MDBX_val *key,
                                                       int flags);
  
  #define MDBX_PS_MODIFY 1
  #define MDBX_PS_ROOTONLY 2
  #define MDBX_PS_FIRST 4
  #define MDBX_PS_LAST 8
  static int __must_check_result mdbx_page_search(MDBX_cursor *mc,
                                                  const MDBX_val *key, int flags);
  static int __must_check_result mdbx_page_merge(MDBX_cursor *csrc,
                                                 MDBX_cursor *cdst);
  static int __must_check_result mdbx_page_flush(MDBX_txn *txn,
                                                 const unsigned keep);
  
  #define MDBX_SPLIT_REPLACE MDBX_APPENDDUP /* newkey is not new */
  static int __must_check_result mdbx_page_split(MDBX_cursor *mc,
                                                 const MDBX_val *newkey,
                                                 MDBX_val *newdata,
                                                 pgno_t newpgno, unsigned nflags);
  
  static int __must_check_result mdbx_read_header(MDBX_env *env, MDBX_meta *meta,
                                                  uint64_t *filesize,
                                                  const int lck_exclusive);
  static int __must_check_result mdbx_sync_locked(MDBX_env *env, unsigned flags,
                                                  MDBX_meta *const pending);
  static int mdbx_env_close0(MDBX_env *env);
  
  static MDBX_node *mdbx_node_search(MDBX_cursor *mc, const MDBX_val *key,
                                     int *exactp);
  
  static int __must_check_result mdbx_node_add_branch(MDBX_cursor *mc,
                                                      unsigned indx,
                                                      const MDBX_val *key,
                                                      pgno_t pgno);
  static int __must_check_result mdbx_node_add_leaf(MDBX_cursor *mc,
                                                    unsigned indx,
                                                    const MDBX_val *key,
                                                    MDBX_val *data,
                                                    unsigned flags);
  static int __must_check_result mdbx_node_add_leaf2(MDBX_cursor *mc,
                                                     unsigned indx,
                                                     const MDBX_val *key);
  
  static void mdbx_node_del(MDBX_cursor *mc, size_t ksize);
  static void mdbx_node_shrink(MDBX_page *mp, unsigned indx);
  static int __must_check_result mdbx_node_move(MDBX_cursor *csrc,
                                                MDBX_cursor *cdst, int fromleft);
  static int __must_check_result mdbx_node_read(MDBX_cursor *mc, MDBX_node *leaf,
                                                MDBX_val *data,
                                                const txnid_t pp_txnid);
  static int __must_check_result mdbx_rebalance(MDBX_cursor *mc);
  static int __must_check_result mdbx_update_key(MDBX_cursor *mc,
                                                 const MDBX_val *key);
  
  static void mdbx_cursor_pop(MDBX_cursor *mc);
  static int __must_check_result mdbx_cursor_push(MDBX_cursor *mc, MDBX_page *mp);
  
  static int __must_check_result mdbx_audit_ex(MDBX_txn *txn,
                                               unsigned retired_stored,
                                               bool dont_filter_gc);
  static __maybe_unused __always_inline int __must_check_result
  mdbx_audit(MDBX_txn *txn) {
    return mdbx_audit_ex(txn, 0, (txn->mt_flags & MDBX_TXN_RDONLY) != 0);
  }
  
  static int __must_check_result mdbx_page_check(MDBX_cursor *const mc,
                                                 const MDBX_page *const mp,
                                                 unsigned options);
  static int __must_check_result mdbx_cursor_check(MDBX_cursor *mc,
                                                   unsigned options);
  static int __must_check_result mdbx_cursor_del0(MDBX_cursor *mc);
  static int __must_check_result mdbx_del0(MDBX_txn *txn, MDBX_dbi dbi,
                                           const MDBX_val *key,
                                           const MDBX_val *data, unsigned flags);
  #define SIBLING_LEFT 0
  #define SIBLING_RIGHT 2
  static int __must_check_result mdbx_cursor_sibling(MDBX_cursor *mc, int dir);
  static int __must_check_result mdbx_cursor_next(MDBX_cursor *mc, MDBX_val *key,
                                                  MDBX_val *data,
                                                  MDBX_cursor_op op);
  static int __must_check_result mdbx_cursor_prev(MDBX_cursor *mc, MDBX_val *key,
                                                  MDBX_val *data,
                                                  MDBX_cursor_op op);
  static int __must_check_result mdbx_cursor_set(MDBX_cursor *mc, MDBX_val *key,
                                                 MDBX_val *data,
                                                 MDBX_cursor_op op, int *exactp);
  static int __must_check_result mdbx_cursor_first(MDBX_cursor *mc, MDBX_val *key,
                                                   MDBX_val *data);
  static int __must_check_result mdbx_cursor_last(MDBX_cursor *mc, MDBX_val *key,
                                                  MDBX_val *data);
  
  static int __must_check_result mdbx_cursor_init(MDBX_cursor *mc, MDBX_txn *txn,
                                                  MDBX_dbi dbi);
  static int __must_check_result mdbx_xcursor_init0(MDBX_cursor *mc);
  static int __must_check_result mdbx_xcursor_init1(MDBX_cursor *mc,
                                                    MDBX_node *node,
                                                    const MDBX_page *mp);
  static int __must_check_result mdbx_xcursor_init2(MDBX_cursor *mc,
                                                    MDBX_xcursor *src_mx,
                                                    bool new_dupdata);
  static void cursor_copy_internal(const MDBX_cursor *csrc, MDBX_cursor *cdst);
  
  static int __must_check_result mdbx_drop0(MDBX_cursor *mc, int subs);
  static int __must_check_result mdbx_fetch_sdb(MDBX_txn *txn, MDBX_dbi dbi);
  static int __must_check_result mdbx_setup_dbx(MDBX_dbx *const dbx,
                                                const MDBX_db *const db,
                                                const unsigned pagesize);
  
  static MDBX_cmp_func cmp_lexical, cmp_reverse, cmp_int_align4, cmp_int_align2,
      cmp_int_unaligned, cmp_lenfast;
  
  static __inline MDBX_cmp_func *get_default_keycmp(unsigned flags);
  static __inline MDBX_cmp_func *get_default_datacmp(unsigned flags);
  
  __cold const char *mdbx_liberr2str(int errnum) {
    /* Table of descriptions for MDBX errors */
    static const char *const tbl[] = {
        "MDBX_KEYEXIST: Key/data pair already exists",
        "MDBX_NOTFOUND: No matching key/data pair found",
        "MDBX_PAGE_NOTFOUND: Requested page not found",
        "MDBX_CORRUPTED: Database is corrupted",
        "MDBX_PANIC: Environment had fatal error",
        "MDBX_VERSION_MISMATCH: DB version mismatch libmdbx",
        "MDBX_INVALID: File is not an MDBX file",
        "MDBX_MAP_FULL: Environment mapsize limit reached",
        "MDBX_DBS_FULL: Too many DBI-handles (maxdbs reached)",
        "MDBX_READERS_FULL: Too many readers (maxreaders reached)",
        NULL /* MDBX_TLS_FULL (-30789): unused in MDBX */,
        "MDBX_TXN_FULL: Transaction has too many dirty pages,"
        " i.e transaction is too big",
        "MDBX_CURSOR_FULL: Cursor stack limit reachedn - this usually indicates"
        " corruption, i.e branch-pages loop",
        "MDBX_PAGE_FULL: Internal error - Page has no more space",
        "MDBX_UNABLE_EXTEND_MAPSIZE: Database engine was unable to extend"
        " mapping, e.g. since address space is unavailable or busy,"
        " or Operation system not supported such operations",
        "MDBX_INCOMPATIBLE: Environment or database is not compatible"
        " with the requested operation or the specified flags",
        "MDBX_BAD_RSLOT: Invalid reuse of reader locktable slot,"
        " e.g. read-transaction already run for current thread",
        "MDBX_BAD_TXN: Transaction is not valid for requested operation,"
        " e.g. had errored and be must aborted, has a child, or is invalid",
        "MDBX_BAD_VALSIZE: Invalid size or alignment of key or data"
        " for target database, either invalid subDB name",
        "MDBX_BAD_DBI: The specified DBI-handle is invalid"
        " or changed by another thread/transaction",
        "MDBX_PROBLEM: Unexpected internal error, transaction should be aborted",
        "MDBX_BUSY: Another write transaction is running,"
        " or environment is already used while opening with MDBX_EXCLUSIVE flag",
    };
  
    if (errnum >= MDBX_KEYEXIST && errnum <= MDBX_BUSY) {
      int i = errnum - MDBX_KEYEXIST;
      return tbl[i];
    }
  
    switch (errnum) {
    case MDBX_SUCCESS:
      return "MDBX_SUCCESS: Successful";
    case MDBX_EMULTIVAL:
      return "MDBX_EMULTIVAL: The specified key has"
             " more than one associated value";
    case MDBX_EBADSIGN:
      return "MDBX_EBADSIGN: Wrong signature of a runtime object(s),"
             " e.g. memory corruption or double-free";
    case MDBX_WANNA_RECOVERY:
      return "MDBX_WANNA_RECOVERY: Database should be recovered,"
             " but this could NOT be done automatically for now"
             " since it opened in read-only mode";
    case MDBX_EKEYMISMATCH:
      return "MDBX_EKEYMISMATCH: The given key value is mismatched to the"
             " current cursor position";
    case MDBX_TOO_LARGE:
      return "MDBX_TOO_LARGE: Database is too large for current system,"
             " e.g. could NOT be mapped into RAM";
    case MDBX_THREAD_MISMATCH:
      return "MDBX_THREAD_MISMATCH: A thread has attempted to use a not"
             " owned object, e.g. a transaction that started by another thread";
    case MDBX_TXN_OVERLAPPING:
      return "MDBX_TXN_OVERLAPPING: Overlapping read and write transactions for"
             " the current thread";
    default:
      return NULL;
    }
  }
  
  const char *__cold mdbx_strerror_r(int errnum, char *buf, size_t buflen) {
    const char *msg = mdbx_liberr2str(errnum);
    if (!msg && buflen > 0 && buflen < INT_MAX) {
  #if defined(_WIN32) || defined(_WIN64)
      const DWORD size = FormatMessageA(
          FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL,
          errnum, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), buf, (DWORD)buflen,
          NULL);
      return size ? buf : "FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM) failed";
  #elif defined(_GNU_SOURCE) && defined(__GLIBC__)
      /* GNU-specific */
      if (errnum > 0)
        msg = strerror_r(errnum, buf, buflen);
  #elif (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
      /* XSI-compliant */
      if (errnum > 0 && strerror_r(errnum, buf, buflen) == 0)
        msg = buf;
  #else
      if (errnum > 0) {
        msg = strerror(errnum);
        if (msg) {
          strncpy(buf, msg, buflen);
          msg = buf;
        }
      }
  #endif
      if (!msg) {
        (void)snprintf(buf, buflen, "error %d", errnum);
        msg = buf;
      }
      buf[buflen - 1] = '\0';
    }
    return msg;
  }
  
  const char *__cold mdbx_strerror(int errnum) {
  #if defined(_WIN32) || defined(_WIN64)
    static char buf[1024];
    return mdbx_strerror_r(errnum, buf, sizeof(buf));
  #else
    const char *msg = mdbx_liberr2str(errnum);
    if (!msg) {
      if (errnum > 0)
        msg = strerror(errnum);
      if (!msg) {
        static char buf[32];
        (void)snprintf(buf, sizeof(buf) - 1, "error %d", errnum);
        msg = buf;
      }
    }
    return msg;
  #endif
  }
  
  #if defined(_WIN32) || defined(_WIN64) /* Bit of madness for Windows */
  const char *mdbx_strerror_r_ANSI2OEM(int errnum, char *buf, size_t buflen) {
    const char *msg = mdbx_liberr2str(errnum);
    if (!msg && buflen > 0 && buflen < INT_MAX) {
      const DWORD size = FormatMessageA(
          FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL,
          errnum, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), buf, (DWORD)buflen,
          NULL);
      if (!size)
        msg = "FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM) failed";
      else if (!CharToOemBuffA(buf, buf, size))
        msg = "CharToOemBuffA() failed";
      else
        msg = buf;
    }
    return msg;
  }
  
  const char *mdbx_strerror_ANSI2OEM(int errnum) {
    static char buf[1024];
    return mdbx_strerror_r_ANSI2OEM(errnum, buf, sizeof(buf));
  }
  #endif /* Bit of madness for Windows */
  
  void __cold mdbx_debug_log_va(int level, const char *function, int line,
                                const char *fmt, va_list args) {
    if (mdbx_debug_logger)
      mdbx_debug_logger(level, function, line, fmt, args);
    else {
  #if defined(_WIN32) || defined(_WIN64)
      if (IsDebuggerPresent()) {
        int prefix_len = 0;
        char *prefix = nullptr;
        if (function && line > 0)
          prefix_len = mdbx_asprintf(&prefix, "%s:%d ", function, line);
        else if (function)
          prefix_len = mdbx_asprintf(&prefix, "%s: ", function);
        else if (line > 0)
          prefix_len = mdbx_asprintf(&prefix, "%d: ", line);
        if (prefix_len > 0 && prefix) {
          OutputDebugStringA(prefix);
          mdbx_free(prefix);
        }
        char *msg = nullptr;
        int msg_len = mdbx_vasprintf(&msg, fmt, args);
        if (msg_len > 0 && msg) {
          OutputDebugStringA(msg);
          mdbx_free(msg);
        }
      }
  #else
      if (function && line > 0)
        fprintf(stderr, "%s:%d ", function, line);
      else if (function)
        fprintf(stderr, "%s: ", function);
      else if (line > 0)
        fprintf(stderr, "%d: ", line);
      vfprintf(stderr, fmt, args);
      fflush(stderr);
  #endif
    }
  }
  
  void __cold mdbx_debug_log(int level, const char *function, int line,
                             const char *fmt, ...) {
    va_list args;
    va_start(args, fmt);
    mdbx_debug_log_va(level, function, line, fmt, args);
    va_end(args);
  }
  
  /* Dump a key in ascii or hexadecimal. */
  const char *mdbx_dump_val(const MDBX_val *key, char *const buf,
                            const size_t bufsize) {
    if (!key)
      return "<null>";
    if (!key->iov_len)
      return "<empty>";
    if (!buf || bufsize < 4)
      return nullptr;
  
    bool is_ascii = true;
    const uint8_t *const data = key->iov_base;
    for (unsigned i = 0; i < key->iov_len; i++)
      if (data[i] < ' ' || data[i] > '~') {
        is_ascii = false;
        break;
      }
  
    if (is_ascii) {
      int len =
          snprintf(buf, bufsize, "%.*s",
                   (key->iov_len > INT_MAX) ? INT_MAX : (int)key->iov_len, data);
      assert(len > 0 && (unsigned)len < bufsize);
      (void)len;
    } else {
      char *const detent = buf + bufsize - 2;
      char *ptr = buf;
      *ptr++ = '<';
      for (unsigned i = 0; i < key->iov_len; i++) {
        const ptrdiff_t left = detent - ptr;
        assert(left > 0);
        int len = snprintf(ptr, left, "%02x", data[i]);
        if (len < 0 || len >= left)
          break;
        ptr += len;
      }
      if (ptr < detent) {
        ptr[0] = '>';
        ptr[1] = '\0';
      }
    }
    return buf;
  }
  
  /*------------------------------------------------------------------------------
   LY: debug stuff */
  
  static const char *mdbx_leafnode_type(MDBX_node *n) {
    static const char *const tp[2][2] = {{"", ": DB"},
                                         {": sub-page", ": sub-DB"}};
    return F_ISSET(node_flags(n), F_BIGDATA)
               ? ": overflow page"
               : tp[F_ISSET(node_flags(n), F_DUPDATA)]
                   [F_ISSET(node_flags(n), F_SUBDATA)];
  }
  
  /* Display all the keys in the page. */
  static __maybe_unused void mdbx_page_list(MDBX_page *mp) {
    pgno_t pgno = mp->mp_pgno;
    const char *type, *state = IS_DIRTY(mp) ? ", dirty" : "";
    MDBX_node *node;
    unsigned i, nkeys, nsize, total = 0;
    MDBX_val key;
    DKBUF;
  
    switch (mp->mp_flags &
            (P_BRANCH | P_LEAF | P_LEAF2 | P_META | P_OVERFLOW | P_SUBP)) {
    case P_BRANCH:
      type = "Branch page";
      break;
    case P_LEAF:
      type = "Leaf page";
      break;
    case P_LEAF | P_SUBP:
      type = "Leaf sub-page";
      break;
    case P_LEAF | P_LEAF2:
      type = "Leaf2 page";
      break;
    case P_LEAF | P_LEAF2 | P_SUBP:
      type = "Leaf2 sub-page";
      break;
    case P_OVERFLOW:
      mdbx_verbose("Overflow page %" PRIaPGNO " pages %u%s\n", pgno, mp->mp_pages,
                   state);
      return;
    case P_META:
      mdbx_verbose("Meta-page %" PRIaPGNO " txnid %" PRIu64 "\n", pgno,
                   page_meta(mp)->mm_txnid_a.inconsistent);
      return;
    default:
      mdbx_verbose("Bad page %" PRIaPGNO " flags 0x%X\n", pgno, mp->mp_flags);
      return;
    }
  
    nkeys = page_numkeys(mp);
    mdbx_verbose("%s %" PRIaPGNO " numkeys %u%s\n", type, pgno, nkeys, state);
  
    for (i = 0; i < nkeys; i++) {
      if (IS_LEAF2(mp)) { /* LEAF2 pages have no mp_ptrs[] or node headers */
        key.iov_len = nsize = mp->mp_leaf2_ksize;
        key.iov_base = page_leaf2key(mp, i, nsize);
        total += nsize;
        mdbx_verbose("key %u: nsize %u, %s\n", i, nsize, DKEY(&key));
        continue;
      }
      node = page_node(mp, i);
      key.iov_len = node_ks(node);
      key.iov_base = node->mn_data;
      nsize = (unsigned)(NODESIZE + key.iov_len);
      if (IS_BRANCH(mp)) {
        mdbx_verbose("key %u: page %" PRIaPGNO ", %s\n", i, node_pgno(node),
                     DKEY(&key));
        total += nsize;
      } else {
        if (F_ISSET(node_flags(node), F_BIGDATA))
          nsize += sizeof(pgno_t);
        else
          nsize += (unsigned)node_ds(node);
        total += nsize;
        nsize += sizeof(indx_t);
        mdbx_verbose("key %u: nsize %u, %s%s\n", i, nsize, DKEY(&key),
                     mdbx_leafnode_type(node));
      }
      total = EVEN(total);
    }
    mdbx_verbose("Total: header %u + contents %u + unused %u\n",
                 IS_LEAF2(mp) ? PAGEHDRSZ : PAGEHDRSZ + mp->mp_lower, total,
                 page_room(mp));
  }
  
  /*----------------------------------------------------------------------------*/
  
  /* Check if there is an initialized xcursor, so XCURSOR_REFRESH() is proper */
  #define XCURSOR_INITED(mc)                                                     \
    ((mc)->mc_xcursor && ((mc)->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED))
  
  /* Update sub-page pointer, if any, in mc->mc_xcursor.
   * Needed when the node which contains the sub-page may have moved.
   * Called with mp = mc->mc_pg[mc->mc_top], ki = mc->mc_ki[mc->mc_top]. */
  #define XCURSOR_REFRESH(mc, mp, ki)                                            \
    do {                                                                         \
      MDBX_page *xr_pg = (mp);                                                   \
      MDBX_node *xr_node = page_node(xr_pg, ki);                                 \
      if ((node_flags(xr_node) & (F_DUPDATA | F_SUBDATA)) == F_DUPDATA)          \
        (mc)->mc_xcursor->mx_cursor.mc_pg[0] = node_data(xr_node);               \
    } while (0)
  
  static __maybe_unused bool cursor_is_tracked(const MDBX_cursor *mc) {
    for (MDBX_cursor *scan = mc->mc_txn->tw.cursors[mc->mc_dbi]; scan;
         scan = scan->mc_next)
      if (mc == ((mc->mc_flags & C_SUB) ? &scan->mc_xcursor->mx_cursor : scan))
        return true;
    return false;
  }
  
  /* Perform act while tracking temporary cursor mn */
  #define WITH_CURSOR_TRACKING(mn, act)                                          \
    do {                                                                         \
      mdbx_cassert(&(mn),                                                        \
                   mn.mc_txn->tw.cursors != NULL /* must be not rdonly txt */);  \
      mdbx_cassert(&(mn), !cursor_is_tracked(&(mn)));                            \
      MDBX_cursor mc_dummy;                                                      \
      MDBX_cursor **tracking_head = &(mn).mc_txn->tw.cursors[mn.mc_dbi];         \
      MDBX_cursor *tracked = &(mn);                                              \
      if ((mn).mc_flags & C_SUB) {                                               \
        mc_dummy.mc_flags = C_INITIALIZED;                                       \
        mc_dummy.mc_top = 0;                                                     \
        mc_dummy.mc_xcursor = (MDBX_xcursor *)&(mn);                             \
        tracked = &mc_dummy;                                                     \
      }                                                                          \
      tracked->mc_next = *tracking_head;                                         \
      *tracking_head = tracked;                                                  \
      { act; }                                                                   \
      *tracking_head = tracked->mc_next;                                         \
    } while (0)
  
  int mdbx_cmp(const MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
               const MDBX_val *b) {
    mdbx_assert(NULL, txn->mt_signature == MDBX_MT_SIGNATURE);
    return txn->mt_dbxs[dbi].md_cmp(a, b);
  }
  
  int mdbx_dcmp(const MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
                const MDBX_val *b) {
    mdbx_assert(NULL, txn->mt_signature == MDBX_MT_SIGNATURE);
    return txn->mt_dbxs[dbi].md_dcmp(a, b);
  }
  
  /* Allocate memory for a page.
   * Re-use old malloc'd pages first for singletons, otherwise just malloc.
   * Set MDBX_TXN_ERROR on failure. */
  static MDBX_page *mdbx_page_malloc(MDBX_txn *txn, unsigned num) {
    MDBX_env *env = txn->mt_env;
    MDBX_page *np = env->me_dpages;
    size_t size = env->me_psize;
    if (likely(num == 1 && np)) {
      ASAN_UNPOISON_MEMORY_REGION(np, size);
      VALGRIND_MEMPOOL_ALLOC(env, np, size);
      VALGRIND_MAKE_MEM_DEFINED(&np->mp_next, sizeof(np->mp_next));
      env->me_dpages = np->mp_next;
    } else {
      size = pgno2bytes(env, num);
      np = mdbx_malloc(size);
      if (unlikely(!np)) {
        txn->mt_flags |= MDBX_TXN_ERROR;
        return np;
      }
      VALGRIND_MEMPOOL_ALLOC(env, np, size);
    }
  
    if ((env->me_flags & MDBX_NOMEMINIT) == 0) {
      /* For a single page alloc, we init everything after the page header.
       * For multi-page, we init the final page; if the caller needed that
       * many pages they will be filling in at least up to the last page. */
      size_t skip = PAGEHDRSZ;
      if (num > 1)
        skip += pgno2bytes(env, num - 1);
      memset((char *)np + skip, 0, size - skip);
    }
  #if MDBX_DEBUG
    np->mp_pgno = 0;
  #endif
    VALGRIND_MAKE_MEM_UNDEFINED(np, size);
    np->mp_flags = 0;
    np->mp_pages = num;
    return np;
  }
  
  /* Free a dirty page */
  static void mdbx_dpage_free(MDBX_env *env, MDBX_page *dp, unsigned pages) {
  #if MDBX_DEBUG
    dp->mp_pgno = MAX_PAGENO + 1;
  #endif
    if (pages == 1) {
      dp->mp_next = env->me_dpages;
      VALGRIND_MEMPOOL_FREE(env, dp);
      env->me_dpages = dp;
    } else {
      /* large pages just get freed directly */
      VALGRIND_MEMPOOL_FREE(env, dp);
      mdbx_free(dp);
    }
  }
  
  /* Return all dirty pages to dpage list */
  static void mdbx_dlist_free(MDBX_txn *txn) {
    MDBX_env *env = txn->mt_env;
    const MDBX_DPL dl = txn->tw.dirtylist;
    const size_t n = dl->length;
  
    for (size_t i = 1; i <= n; i++) {
      MDBX_page *dp = dl[i].ptr;
      mdbx_dpage_free(env, dp, IS_OVERFLOW(dp) ? dp->mp_pages : 1);
    }
  
    mdbx_dpl_clear(dl);
  }
  
  static __always_inline MDBX_db *mdbx_outer_db(MDBX_cursor *mc) {
    mdbx_cassert(mc, (mc->mc_flags & C_SUB) != 0);
    MDBX_xcursor *mx = container_of(mc->mc_db, MDBX_xcursor, mx_db);
    MDBX_cursor_couple *couple = container_of(mx, MDBX_cursor_couple, inner);
    mdbx_cassert(mc, mc->mc_db == &couple->outer.mc_xcursor->mx_db);
    mdbx_cassert(mc, mc->mc_dbx == &couple->outer.mc_xcursor->mx_dbx);
    return couple->outer.mc_db;
  }
  
  static __cold __maybe_unused bool mdbx_dirtylist_check(MDBX_txn *txn) {
    if (!mdbx_audit_enabled())
      return true;
  
    unsigned loose = 0;
    for (unsigned i = txn->tw.dirtylist->length; i > 0; --i) {
      const MDBX_page *const dp = txn->tw.dirtylist[i].ptr;
      if (!dp)
        continue;
      mdbx_tassert(txn, dp->mp_pgno == txn->tw.dirtylist[i].pgno);
      if (unlikely(dp->mp_pgno != txn->tw.dirtylist[i].pgno))
        return false;
  
      mdbx_tassert(txn, dp->mp_flags & P_DIRTY);
      if (unlikely((dp->mp_flags & P_DIRTY) == 0))
        return false;
      if (dp->mp_flags & P_LOOSE) {
        mdbx_tassert(txn, dp->mp_flags == (P_LOOSE | P_DIRTY));
        if (unlikely(dp->mp_flags != (P_LOOSE | P_DIRTY)))
          return false;
        loose += 1;
      }
  
      const unsigned num = IS_OVERFLOW(dp) ? dp->mp_pages : 1;
      mdbx_tassert(txn, txn->mt_next_pgno >= dp->mp_pgno + num);
      if (unlikely(txn->mt_next_pgno < dp->mp_pgno + num))
        return false;
  
      if (i < txn->tw.dirtylist->sorted) {
        mdbx_tassert(txn, txn->tw.dirtylist[i + 1].pgno >= dp->mp_pgno + num);
        if (unlikely(txn->tw.dirtylist[i + 1].pgno < dp->mp_pgno + num))
          return false;
      }
  
      const unsigned rpa = mdbx_pnl_search(txn->tw.reclaimed_pglist, dp->mp_pgno);
      mdbx_tassert(txn, rpa > MDBX_PNL_SIZE(txn->tw.reclaimed_pglist) ||
                            txn->tw.reclaimed_pglist[rpa] != dp->mp_pgno);
      if (rpa <= MDBX_PNL_SIZE(txn->tw.reclaimed_pglist) &&
          unlikely(txn->tw.reclaimed_pglist[rpa] == dp->mp_pgno))
        return false;
      if (num > 1) {
        const unsigned rpb =
            mdbx_pnl_search(txn->tw.reclaimed_pglist, dp->mp_pgno + num - 1);
        mdbx_tassert(txn, rpa == rpb);
        if (unlikely(rpa != rpb))
          return false;
      }
    }
  
    mdbx_tassert(txn, loose == txn->tw.loose_count);
    if (unlikely(loose != txn->tw.loose_count))
      return false;
  
    if (txn->tw.dirtylist->length - txn->tw.dirtylist->sorted < 16) {
      for (unsigned i = 1; i <= MDBX_PNL_SIZE(txn->tw.retired_pages); ++i) {
        const MDBX_page *const dp =
            mdbx_dpl_find(txn->tw.dirtylist, txn->tw.retired_pages[i]);
        mdbx_tassert(txn, !dp);
        if (unlikely(dp))
          return false;
      }
    }
  
    return true;
  }
  
  static void mdbx_refund_reclaimed(MDBX_txn *txn) {
    /* Scanning in descend order */
    pgno_t next_pgno = txn->mt_next_pgno;
    const MDBX_PNL pnl = txn->tw.reclaimed_pglist;
    mdbx_tassert(txn, MDBX_PNL_SIZE(pnl) && MDBX_PNL_MOST(pnl) == next_pgno - 1);
  #if MDBX_PNL_ASCENDING
    unsigned i = MDBX_PNL_SIZE(pnl);
    mdbx_tassert(txn, pnl[i] == next_pgno - 1);
    while (--next_pgno, --i > 0 && pnl[i] == next_pgno - 1)
      ;
    MDBX_PNL_SIZE(pnl) = i;
  #else
    unsigned i = 1;
    mdbx_tassert(txn, pnl[i] == next_pgno - 1);
    unsigned len = MDBX_PNL_SIZE(pnl);
    while (--next_pgno, ++i <= len && pnl[i] == next_pgno - 1)
      ;
    MDBX_PNL_SIZE(pnl) = len -= i - 1;
    for (unsigned move = 0; move < len; ++move)
      pnl[1 + move] = pnl[i + move];
  #endif
    mdbx_verbose("refunded %" PRIaPGNO " pages: %" PRIaPGNO " -> %" PRIaPGNO,
                 txn->mt_next_pgno - next_pgno, txn->mt_next_pgno, next_pgno);
    txn->mt_next_pgno = next_pgno;
    mdbx_tassert(
        txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist, txn->mt_next_pgno));
  }
  
  static void mdbx_refund_loose(MDBX_txn *txn) {
    mdbx_tassert(txn, mdbx_dirtylist_check(txn));
    mdbx_tassert(txn, txn->tw.loose_pages != nullptr);
    mdbx_tassert(txn, txn->tw.loose_count > 0);
  
    const MDBX_DPL dl = txn->tw.dirtylist;
    mdbx_tassert(txn, dl->length >= txn->tw.loose_count);
    mdbx_tassert(txn, txn->tw.spill_pages == nullptr ||
                          dl->length >= MDBX_PNL_SIZE(txn->tw.spill_pages));
  
    pgno_t onstack[MDBX_CACHELINE_SIZE * 8 / sizeof(pgno_t)];
    MDBX_PNL suitable = onstack;
  
    if (dl->length - dl->sorted > txn->tw.loose_count) {
      /* Dirty list is useless since unsorted. */
      if (bytes2pnl(sizeof(onstack)) < txn->tw.loose_count) {
        suitable = mdbx_pnl_alloc(txn->tw.loose_count);
        if (unlikely(!suitable))
          return /* this is not a reason for transaction fail */;
      }
  
      /* Collect loose-pages which may be refunded. */
      mdbx_tassert(txn, txn->mt_next_pgno >= MIN_PAGENO + txn->tw.loose_count);
      pgno_t most = MIN_PAGENO;
      unsigned w = 0;
      for (const MDBX_page *dp = txn->tw.loose_pages; dp; dp = dp->mp_next) {
        mdbx_tassert(txn, dp->mp_flags == (P_LOOSE | P_DIRTY));
        mdbx_tassert(txn, txn->mt_next_pgno > dp->mp_pgno);
        if (likely(txn->mt_next_pgno - txn->tw.loose_count <= dp->mp_pgno)) {
          mdbx_tassert(txn,
                       w < ((suitable == onstack) ? bytes2pnl(sizeof(onstack))
                                                  : MDBX_PNL_ALLOCLEN(suitable)));
          suitable[++w] = dp->mp_pgno;
          most = (dp->mp_pgno > most) ? dp->mp_pgno : most;
        }
      }
  
      if (most + 1 == txn->mt_next_pgno) {
        /* Sort suitable list and refund pages at the tail. */
        MDBX_PNL_SIZE(suitable) = w;
        mdbx_pnl_sort(suitable);
  
        /* Scanning in descend order */
        const int step = MDBX_PNL_ASCENDING ? -1 : 1;
        const int begin = MDBX_PNL_ASCENDING ? MDBX_PNL_SIZE(suitable) : 1;
        const int end = MDBX_PNL_ASCENDING ? 0 : MDBX_PNL_SIZE(suitable) + 1;
        mdbx_tassert(txn, suitable[begin] >= suitable[end - step]);
        mdbx_tassert(txn, most == suitable[begin]);
  
        for (int i = begin + step; i != end; i += step) {
          if (suitable[i] != most - 1)
            break;
          most -= 1;
        }
        const unsigned refunded = txn->mt_next_pgno - most;
        mdbx_debug("refund-suitable %u pages %" PRIaPGNO " -> %" PRIaPGNO,
                   refunded, most, txn->mt_next_pgno);
        txn->tw.loose_count -= refunded;
        txn->tw.dirtyroom += refunded;
        txn->mt_next_pgno = most;
  
        /* Filter-out dirty list */
        unsigned r = 0;
        w = 0;
        if (dl->sorted) {
          do {
            if (dl[++r].pgno < most) {
              if (++w != r)
                dl[w] = dl[r];
            }
          } while (r < dl->sorted);
          dl->sorted = w;
        }
        while (r < dl->length) {
          if (dl[++r].pgno < most) {
            if (++w != r)
              dl[w] = dl[r];
          }
        }
        dl->length = w;
        mdbx_tassert(txn, txn->mt_parent ||
                              txn->tw.dirtyroom + txn->tw.dirtylist->length ==
                                  MDBX_DPL_TXNFULL);
        goto unlink_loose;
      }
    } else {
      /* Dirtylist is mostly sorted, just refund loose pages at the end. */
      mdbx_dpl_sort(dl);
      mdbx_tassert(txn, dl->length < 2 || dl[1].pgno < dl[dl->length].pgno);
      mdbx_tassert(txn, dl->sorted == dl->length);
  
      /* Scan dirtylist tail-forward and cutoff suitable pages. */
      while (dl->length && dl[dl->length].pgno == txn->mt_next_pgno - 1 &&
             dl[dl->length].ptr->mp_flags == (P_LOOSE | P_DIRTY)) {
        MDBX_page *dp = dl[dl->length].ptr;
        mdbx_debug("refund-sorted page %" PRIaPGNO, dp->mp_pgno);
        mdbx_tassert(txn, dp->mp_pgno == dl[dl->length].pgno);
        dl->length -= 1;
      }
  
      if (dl->sorted != dl->length) {
        const unsigned refunded = dl->sorted - dl->length;
        dl->sorted = dl->length;
        txn->tw.loose_count -= refunded;
        txn->tw.dirtyroom += refunded;
        txn->mt_next_pgno -= refunded;
        mdbx_tassert(txn, txn->mt_parent ||
                              txn->tw.dirtyroom + txn->tw.dirtylist->length ==
                                  MDBX_DPL_TXNFULL);
  
        /* Filter-out loose chain & dispose refunded pages. */
      unlink_loose:
        for (MDBX_page **link = &txn->tw.loose_pages; *link;) {
          MDBX_page *dp = *link;
          mdbx_tassert(txn, dp->mp_flags == (P_LOOSE | P_DIRTY));
          if (txn->mt_next_pgno > dp->mp_pgno) {
            link = &dp->mp_next;
          } else {
            *link = dp->mp_next;
            if ((txn->mt_flags & MDBX_WRITEMAP) == 0)
              mdbx_dpage_free(txn->mt_env, dp, 1);
          }
        }
      }
    }
  
    mdbx_tassert(txn, mdbx_dirtylist_check(txn));
    mdbx_tassert(txn, txn->mt_parent ||
                          txn->tw.dirtyroom + txn->tw.dirtylist->length ==
                              MDBX_DPL_TXNFULL);
    if (suitable != onstack)
      mdbx_pnl_free(suitable);
    txn->tw.loose_refund_wl = txn->mt_next_pgno;
  }
  
  static bool mdbx_refund(MDBX_txn *txn) {
    const pgno_t before = txn->mt_next_pgno;
  
    if (txn->tw.loose_pages && txn->tw.loose_refund_wl > txn->mt_next_pgno)
      mdbx_refund_loose(txn);
  
    while (true) {
      if (MDBX_PNL_SIZE(txn->tw.reclaimed_pglist) == 0 ||
          MDBX_PNL_MOST(txn->tw.reclaimed_pglist) != txn->mt_next_pgno - 1)
        break;
  
      mdbx_refund_reclaimed(txn);
      if (!txn->tw.loose_pages || txn->tw.loose_refund_wl <= txn->mt_next_pgno)
        break;
  
      const pgno_t memo = txn->mt_next_pgno;
      mdbx_refund_loose(txn);
      if (memo == txn->mt_next_pgno)
        break;
    }
  
    return before != txn->mt_next_pgno;
  }
  
  static __cold void mdbx_kill_page(MDBX_env *env, MDBX_page *mp, pgno_t pgno,
                                    unsigned npages) {
    mdbx_assert(env, pgno >= NUM_METAS && npages);
    if (IS_DIRTY(mp) || (env->me_flags & MDBX_WRITEMAP)) {
      const size_t bytes = pgno2bytes(env, npages);
      memset(mp, -1, bytes);
      mp->mp_pgno = pgno;
      if ((env->me_flags & MDBX_WRITEMAP) == 0)
        mdbx_pwrite(env->me_lazy_fd, mp, bytes, pgno2bytes(env, pgno));
    } else {
      struct iovec iov[MDBX_COMMIT_PAGES];
      iov[0].iov_len = env->me_psize;
      iov[0].iov_base = (char *)env->me_pbuf + env->me_psize;
      size_t iov_off = pgno2bytes(env, pgno);
      unsigned n = 1;
      while (--npages) {
        iov[n] = iov[0];
        if (++n == MDBX_COMMIT_PAGES) {
          mdbx_pwritev(env->me_lazy_fd, iov, MDBX_COMMIT_PAGES, iov_off,
                       pgno2bytes(env, MDBX_COMMIT_PAGES));
          iov_off += pgno2bytes(env, MDBX_COMMIT_PAGES);
          n = 0;
        }
      }
      mdbx_pwritev(env->me_lazy_fd, iov, n, iov_off, pgno2bytes(env, n));
    }
  }
  
  /* Retire, loosen or free a single page.
   *
   * Saves single pages to a list for future reuse
   * in this same txn. It has been pulled from the GC
   * and already resides on the dirty list, but has been
   * deleted. Use these pages first before pulling again
   * from the GC.
   *
   * If the page wasn't dirtied in this txn, just add it
   * to this txn's free list. */
  
  static int mdbx_page_loose(MDBX_txn *txn, MDBX_page *mp) {
    const unsigned npages = IS_OVERFLOW(mp) ? mp->mp_pages : 1;
    const pgno_t pgno = mp->mp_pgno;
  
    mp->mp_txnid = INVALID_TXNID;
    if (txn->mt_parent) {
      mdbx_tassert(txn, (txn->mt_env->me_flags & MDBX_WRITEMAP) == 0);
      mdbx_tassert(txn, mp != pgno2page(txn->mt_env, pgno));
      /* If txn has a parent, make sure the page is in our dirty list. */
      MDBX_page *dp = mdbx_dpl_find(txn->tw.dirtylist, pgno);
      /* TODO: use extended flag-mask to track parent's dirty-pages */
      if (dp == nullptr) {
        mp->mp_next = txn->tw.retired2parent_pages;
        txn->tw.retired2parent_pages = mp;
        txn->tw.retired2parent_count += npages;
        return MDBX_SUCCESS;
      }
      if (unlikely(mp != dp)) { /* bad cursor? */
        mdbx_error(
            "wrong page 0x%p #%" PRIaPGNO " in the dirtylist, expecting %p",
            __Wpedantic_format_voidptr(dp), pgno, __Wpedantic_format_voidptr(mp));
        txn->mt_flags |= MDBX_TXN_ERROR;
        return MDBX_PROBLEM;
      }
      /* ok, it's ours */
    }
  
    mdbx_debug("loosen page %" PRIaPGNO, pgno);
    const bool is_dirty = IS_DIRTY(mp);
    if (MDBX_DEBUG != 0 ||
        unlikely((txn->mt_env->me_flags & MDBX_PAGEPERTURB) != 0)) {
      mdbx_kill_page(txn->mt_env, mp, pgno, npages);
      VALGRIND_MAKE_MEM_UNDEFINED(mp, PAGEHDRSZ);
    }
    VALGRIND_MAKE_MEM_NOACCESS(page_data(mp),
                               pgno2bytes(txn->mt_env, npages) - PAGEHDRSZ);
    ASAN_POISON_MEMORY_REGION(page_data(mp),
                              pgno2bytes(txn->mt_env, npages) - PAGEHDRSZ);
  
    if (unlikely(npages >
                 1 /* overflow pages doesn't comes to the loose-list */)) {
      if (is_dirty) {
        /* Remove from dirty list */
        MDBX_page *dp = mdbx_dpl_remove(txn->tw.dirtylist, pgno);
        if (unlikely(dp != mp)) {
          mdbx_error("not found page 0x%p #%" PRIaPGNO " in the dirtylist",
                     __Wpedantic_format_voidptr(mp), pgno);
          txn->mt_flags |= MDBX_TXN_ERROR;
          return MDBX_PROBLEM;
        }
        txn->tw.dirtyroom++;
        mdbx_tassert(txn, txn->mt_parent ||
                              txn->tw.dirtyroom + txn->tw.dirtylist->length ==
                                  MDBX_DPL_TXNFULL);
        if ((txn->mt_flags & MDBX_WRITEMAP) == 0)
          mdbx_dpage_free(txn->mt_env, mp, npages);
      }
  
      if (unlikely(pgno + npages == txn->mt_next_pgno)) {
        txn->mt_next_pgno = pgno;
        mdbx_refund(txn);
        return MDBX_SUCCESS;
      }
  
      int rc = mdbx_pnl_insert_range(&txn->tw.reclaimed_pglist, pgno, npages);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      mdbx_tassert(txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist,
                                              txn->mt_next_pgno));
      return MDBX_SUCCESS;
    }
  
    mp->mp_pgno = pgno;
    mp->mp_flags = P_LOOSE | P_DIRTY;
    mp->mp_next = txn->tw.loose_pages;
    txn->tw.loose_pages = mp;
    txn->tw.loose_count++;
    if (unlikely(txn->mt_next_pgno == pgno + 1))
      mdbx_refund(txn);
  
    return MDBX_SUCCESS;
  }
  
  static int mdbx_page_retire(MDBX_cursor *mc, MDBX_page *mp) {
    const unsigned npages = IS_OVERFLOW(mp) ? mp->mp_pages : 1;
    const pgno_t pgno = mp->mp_pgno;
    MDBX_txn *const txn = mc->mc_txn;
  
    if (unlikely(mc->mc_flags & C_SUB)) {
      MDBX_db *outer = mdbx_outer_db(mc);
      mdbx_cassert(mc, !IS_BRANCH(mp) || outer->md_branch_pages > 0);
      outer->md_branch_pages -= IS_BRANCH(mp);
      mdbx_cassert(mc, !IS_LEAF(mp) || outer->md_leaf_pages > 0);
      outer->md_leaf_pages -= IS_LEAF(mp);
      mdbx_cassert(mc, !IS_OVERFLOW(mp));
    }
    mdbx_cassert(mc, !IS_BRANCH(mp) || mc->mc_db->md_branch_pages > 0);
    mc->mc_db->md_branch_pages -= IS_BRANCH(mp);
    mdbx_cassert(mc, !IS_LEAF(mp) || mc->mc_db->md_leaf_pages > 0);
    mc->mc_db->md_leaf_pages -= IS_LEAF(mp);
    mdbx_cassert(mc, !IS_OVERFLOW(mp) || mc->mc_db->md_overflow_pages >= npages);
    mc->mc_db->md_overflow_pages -= IS_OVERFLOW(mp) ? npages : 0;
  
    if (IS_DIRTY(mp)) {
      int rc = mdbx_page_loose(txn, mp);
      if (unlikely(rc != MDBX_SUCCESS))
        mc->mc_flags &= ~(C_INITIALIZED | C_EOF);
      return rc;
    }
  
    if (txn->tw.spill_pages) {
      const unsigned i = mdbx_pnl_exist(txn->tw.spill_pages, pgno << 1);
      if (i) {
        /* This page is no longer spilled */
        mdbx_tassert(txn, i == MDBX_PNL_SIZE(txn->tw.spill_pages) ||
                              txn->tw.spill_pages[i + 1] >= (pgno + npages) << 1);
        txn->tw.spill_pages[i] |= 1;
        if (i == MDBX_PNL_SIZE(txn->tw.spill_pages))
          MDBX_PNL_SIZE(txn->tw.spill_pages) -= 1;
        int rc = mdbx_page_loose(txn, mp);
        if (unlikely(rc != MDBX_SUCCESS))
          mc->mc_flags &= ~(C_INITIALIZED | C_EOF);
        return rc;
      }
    }
  
    mdbx_tassert(txn, mp == pgno2page(txn->mt_env, pgno));
    int rc = mdbx_pnl_append_range(&txn->tw.retired_pages, pgno, npages);
    mdbx_tassert(txn, mdbx_dpl_find(txn->tw.dirtylist, pgno) == nullptr);
    return rc;
  }
  
  static __must_check_result __always_inline int
  mdbx_retire_pgno(MDBX_cursor *mc, const pgno_t pgno) {
    MDBX_page *mp;
    int rc;
    if (mdbx_audit_enabled()) {
      const unsigned save_flags = mc->mc_flags;
      mc->mc_flags |= C_RETIRING;
      rc = mdbx_page_get(mc, pgno, &mp, NULL, mc->mc_txn->mt_txnid);
      if (likely(rc == MDBX_SUCCESS))
        rc = mdbx_page_retire(mc, mp);
      mc->mc_flags = (mc->mc_flags & ~C_RETIRING) | (save_flags & C_RETIRING);
    } else {
      rc = mdbx_page_get(mc, pgno, &mp, NULL, mc->mc_txn->mt_txnid);
      if (likely(rc == MDBX_SUCCESS))
        rc = mdbx_page_retire(mc, mp);
    }
    return rc;
  }
  
  /* Set or clear P_KEEP in dirty, non-overflow, non-sub pages watched by txn.
   *
   * [in] mc      A cursor handle for the current operation.
   * [in] pflags  Flags of the pages to update:
   *                - P_DIRTY to set P_KEEP,
   *                - P_DIRTY|P_KEEP to clear it.
   * [in] all     No shortcuts. Needed except after a full mdbx_page_flush().
   *
   * Returns 0 on success, non-zero on failure. */
  static int mdbx_pages_xkeep(MDBX_cursor *mc, unsigned pflags, bool all) {
    const unsigned Mask = P_SUBP | P_DIRTY | P_LOOSE | P_KEEP;
    MDBX_txn *txn = mc->mc_txn;
    MDBX_cursor *m3, *m0 = mc;
    MDBX_xcursor *mx;
    MDBX_page *mp;
    unsigned i, j;
    int rc = MDBX_SUCCESS;
  
    /* Mark pages seen by cursors: First m0, then tracked cursors */
    for (i = txn->mt_numdbs;;) {
      if (mc->mc_flags & C_INITIALIZED) {
        for (m3 = mc;; m3 = &mx->mx_cursor) {
          mp = NULL;
          for (j = 0; j < m3->mc_snum; j++) {
            mp = m3->mc_pg[j];
            if ((mp->mp_flags & Mask) == pflags)
              mp->mp_flags ^= P_KEEP;
          }
          mx = m3->mc_xcursor;
          /* Proceed to mx if it is at a sub-database */
          if (!(mx && (mx->mx_cursor.mc_flags & C_INITIALIZED)))
            break;
          if (!(mp && IS_LEAF(mp)))
            break;
          if (!(node_flags(page_node(mp, m3->mc_ki[j - 1])) & F_SUBDATA))
            break;
        }
      }
      mc = mc->mc_next;
      for (; !mc || mc == m0; mc = txn->tw.cursors[--i])
        if (i == 0)
          goto mark_done;
    }
  
  mark_done:
    if (all) {
      /* Mark dirty root pages */
      for (i = 0; i < txn->mt_numdbs; i++) {
        if (txn->mt_dbistate[i] & DBI_DIRTY) {
          pgno_t pgno = txn->mt_dbs[i].md_root;
          if (pgno == P_INVALID)
            continue;
          MDBX_page *dp = mdbx_dpl_find(txn->tw.dirtylist, pgno);
          if (dp && (dp->mp_flags & Mask) == pflags)
            dp->mp_flags ^= P_KEEP;
        }
      }
    }
  
    return rc;
  }
  
  /* Spill pages from the dirty list back to disk.
   * This is intended to prevent running into MDBX_TXN_FULL situations,
   * but note that they may still occur in a few cases:
   *
   * 1) our estimate of the txn size could be too small. Currently this
   *  seems unlikely, except with a large number of MDBX_MULTIPLE items.
   *
   * 2) child txns may run out of space if their parents dirtied a
   *  lot of pages and never spilled them. TODO: we probably should do
   *  a preemptive spill during mdbx_txn_begin() of a child txn, if
   *  the parent's dirtyroom is below a given threshold.
   *
   * Otherwise, if not using nested txns, it is expected that apps will
   * not run into MDBX_TXN_FULL any more. The pages are flushed to disk
   * the same way as for a txn commit, e.g. their P_DIRTY flag is cleared.
   * If the txn never references them again, they can be left alone.
   * If the txn only reads them, they can be used without any fuss.
   * If the txn writes them again, they can be dirtied immediately without
   * going thru all of the work of mdbx_page_touch(). Such references are
   * handled by mdbx_page_unspill().
   *
   * Also note, we never spill DB root pages, nor pages of active cursors,
   * because we'll need these back again soon anyway. And in nested txns,
   * we can't spill a page in a child txn if it was already spilled in a
   * parent txn. That would alter the parent txns' data even though
   * the child hasn't committed yet, and we'd have no way to undo it if
   * the child aborted.
   *
   * [in] mc    cursor A cursor handle identifying the transaction and
   *            database for which we are checking space.
   * [in] key   For a put operation, the key being stored.
   * [in] data  For a put operation, the data being stored.
   *
   * Returns 0 on success, non-zero on failure. */
  static int mdbx_page_spill(MDBX_cursor *mc, const MDBX_val *key,
                             const MDBX_val *data) {
    if (mc->mc_flags & C_SUB)
      return MDBX_SUCCESS;
  
    MDBX_txn *txn = mc->mc_txn;
    MDBX_DPL dl = txn->tw.dirtylist;
  
    /* Estimate how much space this op will take */
    pgno_t i = mc->mc_db->md_depth;
    /* Named DBs also dirty the main DB */
    if (mc->mc_dbi >= CORE_DBS)
      i += txn->mt_dbs[MAIN_DBI].md_depth;
    /* For puts, roughly factor in the key+data size */
    if (key)
      i += bytes2pgno(txn->mt_env, node_size(key, data) + txn->mt_env->me_psize);
    i += i; /* double it for good measure */
    pgno_t need = i;
  
    if (txn->tw.dirtyroom > i)
      return MDBX_SUCCESS;
  
    /* Less aggressive spill - we originally spilled the entire dirty list,
     * with a few exceptions for cursor pages and DB root pages. But this
     * turns out to be a lot of wasted effort because in a large txn many
     * of those pages will need to be used again. So now we spill only 1/8th
     * of the dirty pages. Testing revealed this to be a good tradeoff,
     * better than 1/2, 1/4, or 1/10. */
    if (need < MDBX_DPL_TXNFULL / 8)
      need = MDBX_DPL_TXNFULL / 8;
  
    if (!txn->tw.spill_pages) {
      txn->tw.spill_pages = mdbx_pnl_alloc(need);
      if (unlikely(!txn->tw.spill_pages))
        return MDBX_ENOMEM;
    } else {
      /* purge deleted slots */
      MDBX_PNL sl = txn->tw.spill_pages;
      pgno_t num = MDBX_PNL_SIZE(sl), j = 0;
      for (i = 1; i <= num; i++) {
        if ((sl[i] & 1) == 0)
          sl[++j] = sl[i];
      }
      MDBX_PNL_SIZE(sl) = j;
    }
  
    /* Preserve pages which may soon be dirtied again */
    int rc = mdbx_pages_xkeep(mc, P_DIRTY, true);
    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout;
  
    /* Save the page IDs of all the pages we're flushing */
    /* flush from the tail forward, this saves a lot of shifting later on. */
    for (i = dl->length; i && need; i--) {
      pgno_t pn = dl[i].pgno << 1;
      MDBX_page *dp = dl[i].ptr;
      if (dp->mp_flags & (P_LOOSE | P_KEEP))
        continue;
      /* Can't spill twice,
       * make sure it's not already in a parent's spill list. */
      if (txn->mt_parent) {
        MDBX_txn *parent;
        for (parent = txn->mt_parent; parent; parent = parent->mt_parent) {
          if (parent->tw.spill_pages &&
              mdbx_pnl_exist(parent->tw.spill_pages, pn)) {
            dp->mp_flags |= P_KEEP;
            break;
          }
        }
        if (parent)
          continue;
      }
      rc = mdbx_pnl_append(&txn->tw.spill_pages, pn);
      if (unlikely(rc != MDBX_SUCCESS))
        goto bailout;
      need--;
    }
    mdbx_pnl_sort(txn->tw.spill_pages);
  
    /* Flush the spilled part of dirty list */
    rc = mdbx_page_flush(txn, i);
    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout;
  
    /* Reset any dirty pages we kept that page_flush didn't see */
    rc = mdbx_pages_xkeep(mc, P_DIRTY | P_KEEP, i != 0);
  
  bailout:
    txn->mt_flags |= rc ? MDBX_TXN_ERROR : MDBX_TXN_SPILLS;
    return rc;
  }
  
  /*----------------------------------------------------------------------------*/
  
  static __always_inline bool meta_bootid_match(const MDBX_meta *meta) {
    return meta->mm_bootid.x == bootid.x && meta->mm_bootid.y == bootid.y &&
           (bootid.x | bootid.y) != 0;
  }
  
  static bool meta_weak_acceptable(const MDBX_env *env, const MDBX_meta *meta,
                                   const int lck_exclusive) {
    return lck_exclusive ? /* exclusive lock */ meta_bootid_match(meta)
                         : /* db already opened */ env->me_lck &&
                               (env->me_lck->mti_envmode & MDBX_RDONLY) == 0;
  }
  
  #define METAPAGE(env, n) page_meta(pgno2page(env, n))
  #define METAPAGE_END(env) METAPAGE(env, NUM_METAS)
  
  static __inline txnid_t meta_txnid(const MDBX_env *env, const MDBX_meta *meta,
                                     const bool allow_volatile) {
    mdbx_assert(env, meta >= METAPAGE(env, 0) || meta < METAPAGE_END(env));
    txnid_t a = safe64_read(&meta->mm_txnid_a);
    txnid_t b = safe64_read(&meta->mm_txnid_b);
    if (allow_volatile)
      return (a == b) ? a : 0;
    mdbx_assert(env, a == b);
    return a;
  }
  
  static __inline txnid_t mdbx_meta_txnid_stable(const MDBX_env *env,
                                                 const MDBX_meta *meta) {
    return meta_txnid(env, meta, false);
  }
  
  static __inline txnid_t mdbx_meta_txnid_fluid(const MDBX_env *env,
                                                const MDBX_meta *meta) {
    return meta_txnid(env, meta, true);
  }
  
  static __inline void mdbx_meta_update_begin(const MDBX_env *env,
                                              MDBX_meta *meta, txnid_t txnid) {
    mdbx_assert(env, meta >= METAPAGE(env, 0) || meta < METAPAGE_END(env));
    mdbx_assert(env, meta->mm_txnid_a.inconsistent < txnid &&
                         meta->mm_txnid_b.inconsistent < txnid);
    (void)env;
    safe64_update(&meta->mm_txnid_a, txnid);
  }
  
  static __inline void mdbx_meta_update_end(const MDBX_env *env, MDBX_meta *meta,
                                            txnid_t txnid) {
    mdbx_assert(env, meta >= METAPAGE(env, 0) || meta < METAPAGE_END(env));
    mdbx_assert(env, meta->mm_txnid_a.inconsistent == txnid);
    mdbx_assert(env, meta->mm_txnid_b.inconsistent < txnid);
    (void)env;
    mdbx_jitter4testing(true);
    meta->mm_bootid = bootid;
    safe64_update(&meta->mm_txnid_b, txnid);
  }
  
  static __inline void mdbx_meta_set_txnid(const MDBX_env *env, MDBX_meta *meta,
                                           txnid_t txnid) {
    mdbx_assert(env, meta < METAPAGE(env, 0) || meta > METAPAGE_END(env));
    (void)env;
    /* update inconsistent since this function used ONLY for filling meta-image
     * for writing, but not the actual meta-page */
    meta->mm_bootid = bootid;
    meta->mm_txnid_a.inconsistent = txnid;
    meta->mm_txnid_b.inconsistent = txnid;
  }
  
  static __inline uint64_t mdbx_meta_sign(const MDBX_meta *meta) {
    uint64_t sign = MDBX_DATASIGN_NONE;
  #if 0 /* TODO */
    sign = hippeus_hash64(...);
  #else
    (void)meta;
  #endif
    /* LY: newer returns MDBX_DATASIGN_NONE or MDBX_DATASIGN_WEAK */
    return (sign > MDBX_DATASIGN_WEAK) ? sign : ~sign;
  }
  
  enum meta_choise_mode { prefer_last, prefer_steady };
  
  static __inline bool mdbx_meta_ot(const enum meta_choise_mode mode,
                                    const MDBX_env *env, const MDBX_meta *a,
                                    const MDBX_meta *b) {
    mdbx_jitter4testing(true);
    txnid_t txnid_a = mdbx_meta_txnid_fluid(env, a);
    txnid_t txnid_b = mdbx_meta_txnid_fluid(env, b);
  
    mdbx_jitter4testing(true);
    switch (mode) {
    default:
      assert(false);
      __unreachable();
      /* fall through */
      __fallthrough;
    case prefer_steady:
      if (META_IS_STEADY(a) != META_IS_STEADY(b))
        return META_IS_STEADY(b);
      /* fall through */
      __fallthrough;
    case prefer_last:
      mdbx_jitter4testing(true);
      if (txnid_a == txnid_b)
        return META_IS_STEADY(b);
      return txnid_a < txnid_b;
    }
  }
  
  static __inline bool mdbx_meta_eq(const MDBX_env *env, const MDBX_meta *a,
                                    const MDBX_meta *b) {
    mdbx_jitter4testing(true);
    const txnid_t txnid = mdbx_meta_txnid_fluid(env, a);
    if (!txnid || txnid != mdbx_meta_txnid_fluid(env, b))
      return false;
  
    mdbx_jitter4testing(true);
    if (META_IS_STEADY(a) != META_IS_STEADY(b))
      return false;
  
    mdbx_jitter4testing(true);
    return true;
  }
  
  static int mdbx_meta_eq_mask(const MDBX_env *env) {
    MDBX_meta *m0 = METAPAGE(env, 0);
    MDBX_meta *m1 = METAPAGE(env, 1);
    MDBX_meta *m2 = METAPAGE(env, 2);
  
    int rc = mdbx_meta_eq(env, m0, m1) ? 1 : 0;
    if (mdbx_meta_eq(env, m1, m2))
      rc += 2;
    if (mdbx_meta_eq(env, m2, m0))
      rc += 4;
    return rc;
  }
  
  static __inline MDBX_meta *mdbx_meta_recent(const enum meta_choise_mode mode,
                                              const MDBX_env *env, MDBX_meta *a,
                                              MDBX_meta *b) {
    const bool a_older_that_b = mdbx_meta_ot(mode, env, a, b);
    mdbx_assert(env, !mdbx_meta_eq(env, a, b));
    return a_older_that_b ? b : a;
  }
  
  static __inline MDBX_meta *mdbx_meta_ancient(const enum meta_choise_mode mode,
                                               const MDBX_env *env, MDBX_meta *a,
                                               MDBX_meta *b) {
    const bool a_older_that_b = mdbx_meta_ot(mode, env, a, b);
    mdbx_assert(env, !mdbx_meta_eq(env, a, b));
    return a_older_that_b ? a : b;
  }
  
  static __inline MDBX_meta *
  mdbx_meta_mostrecent(const enum meta_choise_mode mode, const MDBX_env *env) {
    MDBX_meta *m0 = METAPAGE(env, 0);
    MDBX_meta *m1 = METAPAGE(env, 1);
    MDBX_meta *m2 = METAPAGE(env, 2);
  
    MDBX_meta *head = mdbx_meta_recent(mode, env, m0, m1);
    head = mdbx_meta_recent(mode, env, head, m2);
    return head;
  }
  
  static MDBX_meta *mdbx_meta_steady(const MDBX_env *env) {
    return mdbx_meta_mostrecent(prefer_steady, env);
  }
  
  static MDBX_meta *mdbx_meta_head(const MDBX_env *env) {
    return mdbx_meta_mostrecent(prefer_last, env);
  }
  
  static txnid_t mdbx_recent_committed_txnid(const MDBX_env *env) {
    while (true) {
      const MDBX_meta *head = mdbx_meta_head(env);
      const txnid_t recent = mdbx_meta_txnid_fluid(env, head);
      mdbx_compiler_barrier();
      if (likely(head == mdbx_meta_head(env) &&
                 recent == mdbx_meta_txnid_fluid(env, head)))
        return recent;
    }
  }
  
  static txnid_t mdbx_recent_steady_txnid(const MDBX_env *env) {
    while (true) {
      const MDBX_meta *head = mdbx_meta_steady(env);
      const txnid_t recent = mdbx_meta_txnid_fluid(env, head);
      mdbx_compiler_barrier();
      if (likely(head == mdbx_meta_steady(env) &&
                 recent == mdbx_meta_txnid_fluid(env, head)))
        return recent;
    }
  }
  
  static const char *mdbx_durable_str(const MDBX_meta *const meta) {
    if (META_IS_STEADY(meta))
      return (meta->mm_datasync_sign == mdbx_meta_sign(meta)) ? "Steady"
                                                              : "Tainted";
    return "Weak";
  }
  
  /*----------------------------------------------------------------------------*/
  
  /* Find oldest txnid still referenced. */
  static txnid_t mdbx_find_oldest(const MDBX_txn *txn) {
    mdbx_tassert(txn, (txn->mt_flags & MDBX_TXN_RDONLY) == 0);
    MDBX_env *env = txn->mt_env;
    const txnid_t edge = mdbx_recent_steady_txnid(env);
    mdbx_tassert(txn, edge <= txn->mt_txnid);
  
    MDBX_lockinfo *const lck = env->me_lck;
    if (unlikely(lck == NULL /* exclusive mode */))
      return env->me_lckless_stub.oldest = edge;
  
    const txnid_t last_oldest = lck->mti_oldest_reader;
    mdbx_tassert(txn, edge >= last_oldest);
    if (likely(last_oldest == edge))
      return edge;
  
    const uint32_t nothing_changed = MDBX_STRING_TETRAD("None");
    const uint32_t snap_readers_refresh_flag = lck->mti_readers_refresh_flag;
    mdbx_jitter4testing(false);
    if (snap_readers_refresh_flag == nothing_changed)
      return last_oldest;
  
    txnid_t oldest = edge;
    lck->mti_readers_refresh_flag = nothing_changed;
    mdbx_flush_incoherent_cpu_writeback();
    const unsigned snap_nreaders = lck->mti_numreaders;
    for (unsigned i = 0; i < snap_nreaders; ++i) {
      if (lck->mti_readers[i].mr_pid) {
        /* mdbx_jitter4testing(true); */
        const txnid_t snap = safe64_read(&lck->mti_readers[i].mr_txnid);
        if (oldest > snap && last_oldest <= /* ignore pending updates */ snap) {
          oldest = snap;
          if (oldest == last_oldest)
            return oldest;
        }
      }
    }
  
    if (oldest != last_oldest) {
      mdbx_notice("update oldest %" PRIaTXN " -> %" PRIaTXN, last_oldest, oldest);
      mdbx_tassert(txn, oldest >= lck->mti_oldest_reader);
      lck->mti_oldest_reader = oldest;
    }
    return oldest;
  }
  
  /* Find largest mvcc-snapshot still referenced. */
  static __cold pgno_t mdbx_find_largest(MDBX_env *env, pgno_t largest) {
    MDBX_lockinfo *const lck = env->me_lck;
    if (likely(lck != NULL /* exclusive mode */)) {
      const unsigned snap_nreaders = lck->mti_numreaders;
      for (unsigned i = 0; i < snap_nreaders; ++i) {
      retry:
        if (lck->mti_readers[i].mr_pid) {
          /* mdbx_jitter4testing(true); */
          const pgno_t snap_pages = lck->mti_readers[i].mr_snapshot_pages_used;
          const txnid_t snap_txnid = safe64_read(&lck->mti_readers[i].mr_txnid);
          mdbx_memory_barrier();
          if (unlikely(snap_pages != lck->mti_readers[i].mr_snapshot_pages_used ||
                       snap_txnid != safe64_read(&lck->mti_readers[i].mr_txnid)))
            goto retry;
          if (largest < snap_pages &&
              lck->mti_oldest_reader <= /* ignore pending updates */ snap_txnid &&
              snap_txnid <= env->me_txn0->mt_txnid)
            largest = snap_pages;
        }
      }
    }
  
    return largest;
  }
  
  /* Add a page to the txn's dirty list */
  static int __must_check_result mdbx_page_dirty(MDBX_txn *txn, MDBX_page *mp) {
    mp->mp_txnid = INVALID_TXNID;
    mp->mp_flags |= P_DIRTY;
    const int rc = mdbx_dpl_append(txn->tw.dirtylist, mp->mp_pgno, mp);
    if (unlikely(rc != MDBX_SUCCESS)) {
      txn->mt_flags |= MDBX_TXN_ERROR;
      return rc;
    }
    txn->tw.dirtyroom--;
    mdbx_tassert(txn, txn->mt_parent ||
                          txn->tw.dirtyroom + txn->tw.dirtylist->length ==
                              MDBX_DPL_TXNFULL);
    return MDBX_SUCCESS;
  }
  
  #if !(defined(_WIN32) || defined(_WIN64))
  static __always_inline __maybe_unused int ignore_enosys(int err) {
  #ifdef ENOSYS
    if (err == ENOSYS)
      return MDBX_RESULT_TRUE;
  #endif /* ENOSYS */
  #ifdef ENOIMPL
    if (err == ENOIMPL)
      return MDBX_RESULT_TRUE;
  #endif /* ENOIMPL */
  #ifdef ENOTSUP
    if (err == ENOTSUP)
      return MDBX_RESULT_TRUE;
  #endif /* ENOTSUP */
  #ifdef ENOSUPP
    if (err == ENOSUPP)
      return MDBX_RESULT_TRUE;
  #endif /* ENOSUPP */
  #ifdef EOPNOTSUPP
    if (err == EOPNOTSUPP)
      return MDBX_RESULT_TRUE;
  #endif /* EOPNOTSUPP */
    if (err == EAGAIN)
      return MDBX_RESULT_TRUE;
    return err;
  }
  #endif /* defined(_WIN32) || defined(_WIN64) */
  
  /* Turn on/off readahead. It's harmful when the DB is larger than RAM. */
  static __cold int mdbx_set_readahead(MDBX_env *env, const size_t offset,
                                       const size_t length, const bool enable) {
    assert(length > 0);
    mdbx_notice("readahead %s %u..%u", enable ? "ON" : "OFF",
                bytes2pgno(env, offset), bytes2pgno(env, offset + length));
  
  #if defined(F_RDAHEAD)
    if (unlikely(fcntl(env->me_lazy_fd, F_RDAHEAD, enable) == -1))
      return errno;
  #endif /* F_RDAHEAD */
  
    if (enable) {
  #if defined(F_RDADVISE)
      struct radvisory hint;
      hint.ra_offset = offset;
      hint.ra_count = length;
      (void)/* Ignore ENOTTY for DB on the ram-disk and so on */ fcntl(
          env->me_lazy_fd, F_RDADVISE, &hint);
  #endif /* F_RDADVISE */
  #if defined(MADV_WILLNEED)
      int err = madvise(env->me_map + offset, length, MADV_WILLNEED)
                    ? ignore_enosys(errno)
                    : MDBX_SUCCESS;
      if (unlikely(MDBX_IS_ERROR(err)))
        return err;
  #elif defined(POSIX_MADV_WILLNEED)
      int err = ignore_enosys(
          posix_madvise(env->me_map + offset, length, POSIX_MADV_WILLNEED));
      if (unlikely(MDBX_IS_ERROR(err)))
        return err;
  #elif defined(_WIN32) || defined(_WIN64)
      if (mdbx_PrefetchVirtualMemory) {
        WIN32_MEMORY_RANGE_ENTRY hint;
        hint.VirtualAddress = env->me_map + offset;
        hint.NumberOfBytes = length;
        (void)mdbx_PrefetchVirtualMemory(GetCurrentProcess(), 1, &hint, 0);
      }
  #elif defined(POSIX_FADV_WILLNEED)
      int err = ignore_enosys(
          posix_fadvise(env->me_lazy_fd, offset, length, POSIX_FADV_WILLNEED));
      if (unlikely(MDBX_IS_ERROR(err)))
        return err;
  #endif /* MADV_WILLNEED */
    } else {
  #if defined(MADV_RANDOM)
      int err = madvise(env->me_map + offset, length, MADV_RANDOM)
                    ? ignore_enosys(errno)
                    : MDBX_SUCCESS;
      if (unlikely(MDBX_IS_ERROR(err)))
        return err;
  #elif defined(POSIX_MADV_RANDOM)
      int err = ignore_enosys(
          posix_madvise(env->me_map + offset, length, POSIX_MADV_RANDOM));
      if (unlikely(MDBX_IS_ERROR(err)))
        return err;
  #elif defined(POSIX_FADV_RANDOM)
      int err = ignore_enosys(
          posix_fadvise(env->me_lazy_fd, offset, length, POSIX_FADV_RANDOM));
      if (unlikely(MDBX_IS_ERROR(err)))
        return err;
  #endif /* MADV_RANDOM */
    }
    return MDBX_SUCCESS;
  }
  
  static __cold int mdbx_mapresize(MDBX_env *env, const pgno_t used_pgno,
                                   const pgno_t size_pgno,
                                   const pgno_t limit_pgno, const bool implicit) {
    if ((env->me_flags & MDBX_WRITEMAP) && *env->me_unsynced_pages) {
      int err = mdbx_msync(&env->me_dxb_mmap, 0,
                           pgno_align2os_bytes(env, used_pgno), true);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
    }
  
    const size_t limit_bytes = pgno_align2os_bytes(env, limit_pgno);
    const size_t size_bytes = pgno_align2os_bytes(env, size_pgno);
    const size_t prev_size = env->me_dxb_mmap.current;
    const size_t prev_limit = env->me_dxb_mmap.limit;
    const void *const prev_addr = env->me_map;
  
    mdbx_verbose("resize datafile/mapping: "
                 "present %" PRIuPTR " -> %" PRIuPTR ", "
                 "limit %" PRIuPTR " -> %" PRIuPTR,
                 prev_size, size_bytes, prev_limit, limit_bytes);
  
    mdbx_assert(env, limit_bytes >= size_bytes);
    mdbx_assert(env, bytes2pgno(env, size_bytes) >= size_pgno);
    mdbx_assert(env, bytes2pgno(env, limit_bytes) >= limit_pgno);
  
  #if defined(_WIN32) || defined(_WIN64)
    /* Acquire guard in exclusive mode for:
     *   - to avoid collision between read and write txns around env->me_dbgeo;
     *   - to avoid attachment of new reading threads (see mdbx_rdt_lock); */
    mdbx_srwlock_AcquireExclusive(&env->me_remap_guard);
    mdbx_handle_array_t *suspended = NULL;
    mdbx_handle_array_t array_onstack;
    int rc = MDBX_SUCCESS;
    if (limit_bytes == env->me_dxb_mmap.limit &&
        size_bytes == env->me_dxb_mmap.current &&
        size_bytes == env->me_dxb_mmap.filesize)
      goto bailout;
  
    /* 1) Windows allows only extending a read-write section, but not a
     *    corresponding mapped view. Therefore in other cases we must suspend
     *    the local threads for safe remap.
     * 2) At least on Windows 10 1803 the entire mapped section is unavailable
     *    for short time during NtExtendSection() or VirtualAlloc() execution.
     * 3) Under Wine runtime environment on Linux a section extending is not
     *    supported. Therefore thread suspending is always required.
     *
     * THEREFORE LOCAL THREADS SUSPENDING IS ALWAYS REQUIRED! */
    array_onstack.limit = ARRAY_LENGTH(array_onstack.handles);
    array_onstack.count = 0;
    suspended = &array_onstack;
    rc = mdbx_suspend_threads_before_remap(env, &suspended);
    if (rc != MDBX_SUCCESS) {
      mdbx_error("failed suspend-for-remap: errcode %d", rc);
      goto bailout;
    }
    const bool mapping_can_be_moved = !implicit;
  #else /* Windows */
    /* Acquire guard to avoid collision between read and write txns
     * around env->me_dbgeo */
    bool mapping_can_be_moved = false;
    int rc = mdbx_fastmutex_acquire(&env->me_remap_guard);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
    if (limit_bytes == env->me_dxb_mmap.limit &&
        size_bytes == env->me_dxb_mmap.current)
      goto bailout;
  
    if (limit_bytes != env->me_dxb_mmap.limit && env->me_lck && !implicit) {
      int err = mdbx_rdt_lock(env) /* lock readers table until remap done */;
      if (unlikely(MDBX_IS_ERROR(err))) {
        rc = err;
        goto bailout;
      }
  
      /* looking for readers from this process */
      MDBX_lockinfo *const lck = env->me_lck;
      const unsigned snap_nreaders = lck->mti_numreaders;
      mapping_can_be_moved = true;
      for (unsigned i = 0; i < snap_nreaders; ++i) {
        if (lck->mti_readers[i].mr_pid == env->me_pid &&
            lck->mti_readers[i].mr_tid != mdbx_thread_self()) {
          /* the base address of the mapping can't be changed since
           * the other reader thread from this process exists. */
          mdbx_rdt_unlock(env);
          mapping_can_be_moved = false;
          break;
        }
      }
    }
  
  #endif /* ! Windows */
  
    if (size_bytes < prev_size) {
      mdbx_notice("resize-MADV_%s %u..%u",
                  (env->me_flags & MDBX_WRITEMAP) ? "REMOVE" : "DONTNEED",
                  size_pgno, bytes2pgno(env, prev_size));
      rc = MDBX_RESULT_TRUE;
  #if defined(MADV_REMOVE)
      if (env->me_flags & MDBX_WRITEMAP)
        rc =
            madvise(env->me_map + size_bytes, prev_size - size_bytes, MADV_REMOVE)
                ? ignore_enosys(errno)
                : MDBX_SUCCESS;
  #endif /* MADV_REMOVE */
  #if defined(MADV_DONTNEED)
      if (rc == MDBX_RESULT_TRUE)
        rc = madvise(env->me_map + size_bytes, prev_size - size_bytes,
                     MADV_DONTNEED)
                 ? ignore_enosys(errno)
                 : MDBX_SUCCESS;
  #elif defined(POSIX_MADV_DONTNEED)
      if (rc == MDBX_RESULT_TRUE)
        rc = ignore_enosys(posix_madvise(env->me_map + size_bytes,
                                         prev_size - size_bytes,
                                         POSIX_MADV_DONTNEED));
  #elif defined(POSIX_FADV_DONTNEED)
      if (rc == MDBX_RESULT_TRUE)
        rc = ignore_enosys(posix_fadvise(env->me_lazy_fd, size_bytes,
                                         prev_size - size_bytes,
                                         POSIX_FADV_DONTNEED));
  #endif /* MADV_DONTNEED */
      if (unlikely(MDBX_IS_ERROR(rc)))
        goto bailout;
      if (*env->me_discarded_tail > size_pgno)
        *env->me_discarded_tail = size_pgno;
    }
  
    rc = mdbx_mresize(env->me_flags, &env->me_dxb_mmap, size_bytes, limit_bytes,
                      mapping_can_be_moved);
    if (rc == MDBX_SUCCESS && (env->me_flags & MDBX_NORDAHEAD) == 0) {
      const int readahead =
          mdbx_is_readahead_reasonable(size_bytes, -(intptr_t)prev_size);
      if (readahead == MDBX_RESULT_FALSE)
        rc = mdbx_set_readahead(
            env, 0, (size_bytes > prev_size) ? size_bytes : prev_size, false);
      else if (readahead == MDBX_RESULT_TRUE) {
        const size_t readahead_pivot =
            (limit_bytes != prev_limit || env->me_dxb_mmap.address != prev_addr
  #if defined(_WIN32) || defined(_WIN64)
             || prev_size > size_bytes
  #endif /* Windows */
             )
                ? 0 /* reassign readahead to the entire map
                       because it was remapped */
                : prev_size;
        if (size_bytes > readahead_pivot) {
          *env->me_discarded_tail = size_pgno;
          rc = mdbx_set_readahead(env, readahead_pivot,
                                  size_bytes - readahead_pivot, true);
        }
      }
    }
  
  bailout:
    if (rc == MDBX_SUCCESS) {
  #if defined(_WIN32) || defined(_WIN64)
      mdbx_assert(env, size_bytes == env->me_dxb_mmap.current);
      mdbx_assert(env, size_bytes <= env->me_dxb_mmap.filesize);
      mdbx_assert(env, limit_bytes == env->me_dxb_mmap.limit);
  #endif /* Windows */
  #ifdef MDBX_USE_VALGRIND
      if (prev_limit != env->me_dxb_mmap.limit || prev_addr != env->me_map) {
        VALGRIND_DISCARD(env->me_valgrind_handle);
        env->me_valgrind_handle = 0;
        if (env->me_dxb_mmap.limit)
          env->me_valgrind_handle =
              VALGRIND_CREATE_BLOCK(env->me_map, env->me_dxb_mmap.limit, "mdbx");
      }
  #endif /* MDBX_USE_VALGRIND */
    } else {
      if (rc != MDBX_UNABLE_EXTEND_MAPSIZE) {
        mdbx_error("failed resize datafile/mapping: "
                   "present %" PRIuPTR " -> %" PRIuPTR ", "
                   "limit %" PRIuPTR " -> %" PRIuPTR ", errcode %d",
                   prev_size, size_bytes, prev_limit, limit_bytes, rc);
      } else {
        mdbx_warning("unable resize datafile/mapping: "
                     "present %" PRIuPTR " -> %" PRIuPTR ", "
                     "limit %" PRIuPTR " -> %" PRIuPTR ", errcode %d",
                     prev_size, size_bytes, prev_limit, limit_bytes, rc);
      }
      if (!env->me_dxb_mmap.address) {
        env->me_flags |= MDBX_FATAL_ERROR;
        if (env->me_txn)
          env->me_txn->mt_flags |= MDBX_TXN_ERROR;
        rc = MDBX_PANIC;
      }
    }
  
  #if defined(_WIN32) || defined(_WIN64)
    int err = MDBX_SUCCESS;
    mdbx_srwlock_ReleaseExclusive(&env->me_remap_guard);
    if (suspended) {
      err = mdbx_resume_threads_after_remap(suspended);
      if (suspended != &array_onstack)
        mdbx_free(suspended);
    }
  #else
    if (env->me_lck && mapping_can_be_moved)
      mdbx_rdt_unlock(env);
    int err = mdbx_fastmutex_release(&env->me_remap_guard);
  #endif /* Windows */
    if (err != MDBX_SUCCESS) {
      mdbx_fatal("failed resume-after-remap: errcode %d", err);
      return MDBX_PANIC;
    }
    return rc;
  }
  
  static __cold int mdbx_mapresize_implicit(MDBX_env *env, const pgno_t used_pgno,
                                            const pgno_t size_pgno,
                                            const pgno_t limit_pgno) {
    const pgno_t mapped_pgno = bytes2pgno(env, env->me_dxb_mmap.limit);
    mdbx_assert(env, mapped_pgno >= used_pgno);
    return mdbx_mapresize(
        env, used_pgno, size_pgno,
        (size_pgno > mapped_pgno)
            ? limit_pgno
            : /* The actual mapsize may be less since the geo.upper may be changed
                 by other process. So, avoids remapping until it necessary. */
            mapped_pgno,
        true);
  }
  
  static int mdbx_meta_unsteady(MDBX_env *env, const txnid_t last_steady,
                                MDBX_meta *const meta) {
    const uint64_t wipe = MDBX_DATASIGN_NONE;
    if (unlikely(META_IS_STEADY(meta)) &&
        mdbx_meta_txnid_stable(env, meta) <= last_steady) {
      mdbx_warning("wipe txn #%" PRIaTXN ", meta %" PRIaPGNO, last_steady,
                   data_page(meta)->mp_pgno);
      if (env->me_flags & MDBX_WRITEMAP)
        meta->mm_datasync_sign = wipe;
      else
        return mdbx_pwrite(env->me_lazy_fd, &wipe, sizeof(meta->mm_datasync_sign),
                           (uint8_t *)&meta->mm_datasync_sign - env->me_map);
    }
    return MDBX_SUCCESS;
  }
  
  __cold static int mdbx_wipe_steady(MDBX_env *env, const txnid_t last_steady) {
    int err = mdbx_meta_unsteady(env, last_steady, METAPAGE(env, 0));
    if (unlikely(err != MDBX_SUCCESS))
      return err;
    err = mdbx_meta_unsteady(env, last_steady, METAPAGE(env, 1));
    if (unlikely(err != MDBX_SUCCESS))
      return err;
    err = mdbx_meta_unsteady(env, last_steady, METAPAGE(env, 2));
    if (unlikely(err != MDBX_SUCCESS))
      return err;
  
    if (env->me_flags & MDBX_WRITEMAP) {
      mdbx_flush_incoherent_cpu_writeback();
      err = mdbx_msync(&env->me_dxb_mmap, 0, pgno_align2os_bytes(env, NUM_METAS),
                       false);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
    } else {
  #if MDBX_USE_SYNCFILERANGE
      static bool syncfilerange_unavailable;
      if (likely(!syncfilerange_unavailable)) {
        if (likely(!sync_file_range(
                env->me_lazy_fd, 0, pgno2bytes(env, NUM_METAS),
                SYNC_FILE_RANGE_WRITE | SYNC_FILE_RANGE_WAIT_AFTER)))
          goto done_filesync;
        err = errno;
        if (ignore_enosys(err) != MDBX_RESULT_TRUE)
          return err;
        syncfilerange_unavailable = true;
      }
  #endif /* MDBX_USE_SYNCFILERANGE */
      err = mdbx_fsync(env->me_lazy_fd, MDBX_SYNC_DATA);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
  #if MDBX_USE_SYNCFILERANGE
    done_filesync:
  #endif /* MDBX_USE_SYNCFILERANGE */
      mdbx_flush_incoherent_mmap(env->me_map, pgno2bytes(env, NUM_METAS),
                                 env->me_os_psize);
    }
  
    if (likely(env->me_lck))
      /* force oldest refresh */
      env->me_lck->mti_readers_refresh_flag = true;
    return MDBX_SUCCESS;
  }
  
  static __inline txnid_t pp_txnid4chk(const MDBX_page *mp, const MDBX_txn *txn) {
    return IS_DIRTY(mp)
               ? txn->mt_txnid - 1
               : (/* maybe zero in legacy DB */ mp->mp_txnid ? mp->mp_txnid
                                                             : MIN_TXNID);
  }
  
  static __inline txnid_t pp_txnid2chk(const MDBX_txn *txn) {
  #ifdef MDBX_DEBUG_LEGACY
    if (txn->mt_txnid < 2222)
      return 0;
  #endif
    return txn->mt_txnid;
  }
  
  /* Allocate page numbers and memory for writing.  Maintain mt_last_reclaimed,
   * mt_reclaimed_pglist and mt_next_pgno.  Set MDBX_TXN_ERROR on failure.
   *
   * If there are free pages available from older transactions, they
   * are re-used first. Otherwise allocate a new page at mt_next_pgno.
   * Do not modify the GC, just merge GC records into mt_reclaimed_pglist
   * and move mt_last_reclaimed to say which records were consumed.  Only this
   * function can create mt_reclaimed_pglist and move
   * mt_last_reclaimed/mt_next_pgno.
   *
   * [in] mc    cursor A cursor handle identifying the transaction and
   *            database for which we are allocating.
   * [in] num   the number of pages to allocate.
   * [out] mp   Address of the allocated page(s). Requests for multiple pages
   *            will always be satisfied by a single contiguous chunk of memory.
   *
   * Returns 0 on success, non-zero on failure.*/
  
  #define MDBX_ALLOC_CACHE 1
  #define MDBX_ALLOC_GC 2
  #define MDBX_ALLOC_NEW 4
  #define MDBX_ALLOC_ALL (MDBX_ALLOC_CACHE | MDBX_ALLOC_GC | MDBX_ALLOC_NEW)
  
  __hot static int mdbx_page_alloc(MDBX_cursor *mc, const unsigned num,
                                   MDBX_page **const mp, int flags) {
    int rc;
    MDBX_txn *txn = mc->mc_txn;
    MDBX_env *env = txn->mt_env;
    MDBX_page *np;
  
    if (likely(flags & MDBX_ALLOC_GC)) {
      flags |= env->me_flags & (MDBX_COALESCE | MDBX_LIFORECLAIM);
      if (unlikely(mc->mc_flags & C_RECLAIMING)) {
        /* If mc is updating the GC, then the retired-list cannot play
         * catch-up with itself by growing while trying to save it. */
        flags &= ~MDBX_ALLOC_GC;
      } else if (unlikely(txn->mt_dbs[FREE_DBI].md_entries == 0)) {
        /* avoid (recursive) search inside empty tree and while tree is updating,
         * https://github.com/erthink/libmdbx/issues/31 */
        flags &= ~MDBX_ALLOC_GC;
      }
    }
  
    if (likely(num == 1 && (flags & MDBX_ALLOC_CACHE) != 0)) {
      /* If there are any loose pages, just use them */
      mdbx_assert(env, mp && num);
      if (likely(txn->tw.loose_pages)) {
        if (txn->tw.loose_refund_wl > txn->mt_next_pgno) {
          mdbx_refund(txn);
          if (unlikely(!txn->tw.loose_pages))
            goto skip_cache;
        }
  
        np = txn->tw.loose_pages;
        txn->tw.loose_pages = np->mp_next;
        txn->tw.loose_count--;
        mdbx_debug("db %d use loose page %" PRIaPGNO, DDBI(mc), np->mp_pgno);
        mdbx_tassert(txn, np->mp_pgno < txn->mt_next_pgno);
        mdbx_ensure(env, np->mp_pgno >= NUM_METAS);
        VALGRIND_MAKE_MEM_UNDEFINED(page_data(np), page_space(txn->mt_env));
        ASAN_UNPOISON_MEMORY_REGION(page_data(np), page_space(txn->mt_env));
        np->mp_flags = P_DIRTY;
        np->mp_txnid = INVALID_TXNID;
        *mp = np;
        return MDBX_SUCCESS;
      }
    }
  skip_cache:
  
    mdbx_tassert(
        txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist, txn->mt_next_pgno));
    pgno_t pgno, *re_list = txn->tw.reclaimed_pglist;
    unsigned range_begin = 0, re_len = MDBX_PNL_SIZE(re_list);
    txnid_t oldest = 0, last = 0;
    const unsigned wanna_range = num - 1;
  
    while (true) { /* hsr-kick retry loop */
      MDBX_cursor_couple recur;
      for (MDBX_cursor_op op = MDBX_FIRST;;
           op = (flags & MDBX_LIFORECLAIM) ? MDBX_PREV : MDBX_NEXT) {
        MDBX_val key, data;
  
        /* Seek a big enough contiguous page range.
         * Prefer pages with lower pgno. */
        mdbx_tassert(txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist,
                                                txn->mt_next_pgno));
        if (likely(flags & MDBX_ALLOC_CACHE) && re_len > wanna_range &&
            (!(flags & MDBX_COALESCE) || op == MDBX_FIRST)) {
          mdbx_tassert(txn, MDBX_PNL_LAST(re_list) < txn->mt_next_pgno &&
                                MDBX_PNL_FIRST(re_list) < txn->mt_next_pgno);
          range_begin = MDBX_PNL_ASCENDING ? 1 : re_len;
          pgno = MDBX_PNL_LEAST(re_list);
          if (likely(wanna_range == 0))
            goto done;
  #if MDBX_PNL_ASCENDING
          mdbx_tassert(txn, pgno == re_list[1] && range_begin == 1);
          while (true) {
            unsigned range_end = range_begin + wanna_range;
            if (re_list[range_end] - pgno == wanna_range)
              goto done;
            if (range_end == re_len)
              break;
            pgno = re_list[++range_begin];
          }
  #else
          mdbx_tassert(txn, pgno == re_list[re_len] && range_begin == re_len);
          while (true) {
            if (re_list[range_begin - wanna_range] - pgno == wanna_range)
              goto done;
            if (range_begin == wanna_range)
              break;
            pgno = re_list[--range_begin];
          }
  #endif /* MDBX_PNL sort-order */
        }
  
        if (op == MDBX_FIRST) { /* 1st iteration, setup cursor, etc */
          if (unlikely(txn->tw.dirtyroom < txn->mt_dbs[FREE_DBI].md_depth) &&
              !(txn->mt_dbistate[FREE_DBI] & DBI_DIRTY)) {
            /* If our dirty list is already full, we can't touch GC */
            flags &= ~MDBX_ALLOC_GC;
          }
          if (unlikely(!(flags & MDBX_ALLOC_GC)))
            break /* reclaiming is prohibited for now */;
  
          /* Prepare to fetch more and coalesce */
          oldest = (flags & MDBX_LIFORECLAIM) ? mdbx_find_oldest(txn)
                                              : *env->me_oldest;
          rc = mdbx_cursor_init(&recur.outer, txn, FREE_DBI);
          if (unlikely(rc != MDBX_SUCCESS))
            goto fail;
          if (flags & MDBX_LIFORECLAIM) {
            /* Begin from oldest reader if any */
            if (oldest > MIN_TXNID) {
              last = oldest - 1;
              op = MDBX_SET_RANGE;
            }
          } else if (txn->tw.last_reclaimed) {
            /* Continue lookup from txn->tw.last_reclaimed to oldest reader */
            last = txn->tw.last_reclaimed;
            op = MDBX_SET_RANGE;
          }
  
          key.iov_base = &last;
          key.iov_len = sizeof(last);
        }
  
        if (!(flags & MDBX_LIFORECLAIM)) {
          /* Do not try fetch more if the record will be too recent */
          if (op != MDBX_FIRST && ++last >= oldest) {
            oldest = mdbx_find_oldest(txn);
            if (oldest <= last)
              break;
          }
        }
  
        rc = mdbx_cursor_get(&recur.outer, &key, NULL, op);
        if (rc == MDBX_NOTFOUND && (flags & MDBX_LIFORECLAIM)) {
          if (op == MDBX_SET_RANGE)
            continue;
          txnid_t snap = mdbx_find_oldest(txn);
          if (oldest < snap) {
            oldest = snap;
            last = oldest - 1;
            key.iov_base = &last;
            key.iov_len = sizeof(last);
            op = MDBX_SET_RANGE;
            rc = mdbx_cursor_get(&recur.outer, &key, NULL, op);
          }
        }
        if (unlikely(rc)) {
          if (rc == MDBX_NOTFOUND)
            break;
          goto fail;
        }
  
        if (unlikely(key.iov_len != sizeof(txnid_t))) {
          rc = MDBX_CORRUPTED;
          goto fail;
        }
        last = unaligned_peek_u64(4, key.iov_base);
        if (unlikely(last < MIN_TXNID || last > MAX_TXNID)) {
          rc = MDBX_CORRUPTED;
          goto fail;
        }
        if (oldest <= last) {
          oldest = mdbx_find_oldest(txn);
          if (oldest <= last) {
            if (flags & MDBX_LIFORECLAIM)
              continue;
            break;
          }
        }
  
        if (flags & MDBX_LIFORECLAIM) {
          /* skip IDs of records that already reclaimed */
          if (txn->tw.lifo_reclaimed) {
            size_t i;
            for (i = (size_t)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed); i > 0; --i)
              if (txn->tw.lifo_reclaimed[i] == last)
                break;
            if (i)
              continue;
          }
        }
  
        /* Reading next GC record */
        np = recur.outer.mc_pg[recur.outer.mc_top];
        if (unlikely((rc = mdbx_node_read(
                          &recur.outer,
                          page_node(np, recur.outer.mc_ki[recur.outer.mc_top]),
                          &data, pp_txnid4chk(np, txn))) != MDBX_SUCCESS))
          goto fail;
  
        if ((flags & MDBX_LIFORECLAIM) && !txn->tw.lifo_reclaimed) {
          txn->tw.lifo_reclaimed = mdbx_txl_alloc();
          if (unlikely(!txn->tw.lifo_reclaimed)) {
            rc = MDBX_ENOMEM;
            goto fail;
          }
        }
  
        /* Append PNL from GC record to tw.reclaimed_pglist */
        mdbx_cassert(mc, (mc->mc_flags & C_GCFREEZE) == 0);
        pgno_t *gc_pnl = (pgno_t *)data.iov_base;
        mdbx_tassert(txn, data.iov_len >= MDBX_PNL_SIZEOF(gc_pnl));
        if (unlikely(data.iov_len < MDBX_PNL_SIZEOF(gc_pnl) ||
                     !mdbx_pnl_check(gc_pnl, txn->mt_next_pgno))) {
          rc = MDBX_CORRUPTED;
          goto fail;
        }
        const unsigned gc_len = MDBX_PNL_SIZE(gc_pnl);
        /* TODO: provide a user-configurable threshold */
        const unsigned threshold_2_stop_gc_reclaiming = MDBX_PNL_MAX / 4;
        if (unlikely(gc_len + MDBX_PNL_SIZE(txn->tw.reclaimed_pglist) >
                     threshold_2_stop_gc_reclaiming) &&
            (pgno_add(txn->mt_next_pgno, num) <= txn->mt_geo.upper ||
             gc_len + MDBX_PNL_SIZE(txn->tw.reclaimed_pglist) >=
                 MDBX_PNL_MAX / 16 * 15)) {
          /* Stop reclaiming to avoid overflow the page list.
           * This is a rare case while search for a continuously multi-page region
           * in a large database. https://github.com/erthink/libmdbx/issues/123 */
          flags &= ~MDBX_ALLOC_GC;
          if (unlikely((flags & MDBX_ALLOC_ALL) == 0)) {
            /* Oh, we can't do anything */
            rc = MDBX_TXN_FULL;
            goto fail;
          }
          break;
        }
        rc = mdbx_pnl_need(&txn->tw.reclaimed_pglist, gc_len);
        if (unlikely(rc != MDBX_SUCCESS))
          goto fail;
        re_list = txn->tw.reclaimed_pglist;
  
        /* Remember ID of GC record */
        if (flags & MDBX_LIFORECLAIM) {
          rc = mdbx_txl_append(&txn->tw.lifo_reclaimed, last);
          if (unlikely(rc != MDBX_SUCCESS))
            goto fail;
        }
        txn->tw.last_reclaimed = last;
  
        if (mdbx_log_enabled(MDBX_LOG_EXTRA)) {
          mdbx_debug_extra("PNL read txn %" PRIaTXN " root %" PRIaPGNO
                           " num %u, PNL",
                           last, txn->mt_dbs[FREE_DBI].md_root, gc_len);
          unsigned i;
          for (i = gc_len; i; i--)
            mdbx_debug_extra_print(" %" PRIaPGNO, gc_pnl[i]);
          mdbx_debug_extra_print("%s", "\n");
        }
  
        /* Merge in descending sorted order */
        const unsigned prev_re_len = MDBX_PNL_SIZE(re_list);
        mdbx_pnl_xmerge(re_list, gc_pnl);
        /* re-check to avoid duplicates */
        if (unlikely(!mdbx_pnl_check(re_list, txn->mt_next_pgno))) {
          rc = MDBX_CORRUPTED;
          goto fail;
        }
  
        re_len = MDBX_PNL_SIZE(re_list);
        mdbx_tassert(txn, re_len == 0 || re_list[re_len] < txn->mt_next_pgno);
        if (re_len && unlikely(MDBX_PNL_MOST(re_list) == txn->mt_next_pgno - 1)) {
          /* Refund suitable pages into "unallocated" space */
          mdbx_refund(txn);
          re_list = txn->tw.reclaimed_pglist;
          re_len = MDBX_PNL_SIZE(re_list);
        }
  
        if (unlikely((flags & MDBX_ALLOC_CACHE) == 0)) {
          /* Done for a kick-reclaim mode, actually no page needed */
          return MDBX_SUCCESS;
        }
  
        /* Don't try to coalesce too much. */
        if (unlikely(re_len > MDBX_DPL_TXNFULL / 42))
          break;
        if (re_len /* current size */ >= env->me_maxgc_ov1page ||
            (re_len > prev_re_len && re_len - prev_re_len /* delta from prev */ >=
                                         env->me_maxgc_ov1page / 2))
          flags &= ~MDBX_COALESCE;
      }
  
      if ((flags & (MDBX_COALESCE | MDBX_ALLOC_CACHE)) == MDBX_ALLOC_CACHE &&
          re_len > wanna_range) {
        range_begin = MDBX_PNL_ASCENDING ? 1 : re_len;
        pgno = MDBX_PNL_LEAST(re_list);
        if (likely(wanna_range == 0))
          goto done;
  #if MDBX_PNL_ASCENDING
        mdbx_tassert(txn, pgno == re_list[1] && range_begin == 1);
        while (true) {
          unsigned range_end = range_begin + wanna_range;
          if (re_list[range_end] - pgno == wanna_range)
            goto done;
          if (range_end == re_len)
            break;
          pgno = re_list[++range_begin];
        }
  #else
        mdbx_tassert(txn, pgno == re_list[re_len] && range_begin == re_len);
        while (true) {
          if (re_list[range_begin - wanna_range] - pgno == wanna_range)
            goto done;
          if (range_begin == wanna_range)
            break;
          pgno = re_list[--range_begin];
        }
  #endif /* MDBX_PNL sort-order */
      }
  
      /* There is no suitable pages in the GC and to be able to allocate
       * we should CHOICE one of:
       *  - make a new steady checkpoint if reclaiming was stopped by
       *    the last steady-sync, or wipe it in the MDBX_UTTERLY_NOSYNC mode;
       *  - kick lagging reader(s) if reclaiming was stopped by ones of it.
       *  - extend the database file. */
  
      /* Will use new pages from the map if nothing is suitable in the GC. */
      range_begin = 0;
      pgno = txn->mt_next_pgno;
      const pgno_t next = pgno_add(pgno, num);
  
      if (flags & MDBX_ALLOC_GC) {
        const MDBX_meta *const head = mdbx_meta_head(env);
        MDBX_meta *const steady = mdbx_meta_steady(env);
        /* does reclaiming stopped at the last steady point? */
        if (head != steady && META_IS_STEADY(steady) &&
            oldest == mdbx_meta_txnid_stable(env, steady)) {
          mdbx_debug("gc-kick-steady: head %" PRIaTXN "-%s, tail %" PRIaTXN
                     "-%s, oldest %" PRIaTXN,
                     mdbx_meta_txnid_stable(env, head), mdbx_durable_str(head),
                     mdbx_meta_txnid_stable(env, steady),
                     mdbx_durable_str(steady), oldest);
          rc = MDBX_RESULT_TRUE;
          const pgno_t autosync_threshold = *env->me_autosync_threshold;
          const uint64_t autosync_period = *env->me_autosync_period;
          /* wipe the last steady-point if one of:
           *  - UTTERLY_NOSYNC mode AND auto-sync threshold is NOT specified
           *  - UTTERLY_NOSYNC mode AND free space at steady-point is exhausted
           * otherwise, make a new steady-point if one of:
           *  - auto-sync threshold is specified and reached;
           *  - upper limit of database size is reached;
           *  - database is full (with the current file size)
           *       AND auto-sync threshold it NOT specified */
          if (F_ISSET(env->me_flags, MDBX_UTTERLY_NOSYNC) &&
              ((autosync_threshold | autosync_period) == 0 ||
               next >= steady->mm_geo.now)) {
            /* wipe steady checkpoint in MDBX_UTTERLY_NOSYNC mode
             * without any auto-sync threshold(s). */
            rc = mdbx_wipe_steady(env, oldest);
            mdbx_debug("gc-wipe-steady, rc %d", rc);
            mdbx_assert(env, steady != mdbx_meta_steady(env));
          } else if ((flags & MDBX_ALLOC_NEW) == 0 ||
                     (autosync_threshold &&
                      *env->me_unsynced_pages >= autosync_threshold) ||
                     (autosync_period &&
                      mdbx_osal_monotime() - *env->me_sync_timestamp >=
                          autosync_period) ||
                     next >= txn->mt_geo.upper ||
                     (next >= txn->mt_end_pgno &&
                      (autosync_threshold | autosync_period) == 0)) {
            /* make steady checkpoint. */
            MDBX_meta meta = *head;
            rc = mdbx_sync_locked(env, env->me_flags & MDBX_WRITEMAP, &meta);
            mdbx_debug("gc-make-steady, rc %d", rc);
            mdbx_assert(env, steady != mdbx_meta_steady(env));
          }
          if (rc == MDBX_SUCCESS) {
            if (mdbx_find_oldest(txn) > oldest)
              continue;
            /* it is reasonable check/kick lagging reader(s) here,
             * since we made a new steady point or wipe the last. */
            if (oldest < txn->mt_txnid - MDBX_TXNID_STEP &&
                mdbx_kick_longlived_readers(env, oldest) > oldest)
              continue;
          } else if (unlikely(rc != MDBX_RESULT_TRUE))
            goto fail;
        }
      }
  
      /* don't kick lagging reader(s) if is enough unallocated space
       * at the end of database file. */
      if ((flags & MDBX_ALLOC_NEW) && next <= txn->mt_end_pgno)
        goto done;
      if ((flags & MDBX_ALLOC_GC) && oldest < txn->mt_txnid - MDBX_TXNID_STEP &&
          mdbx_kick_longlived_readers(env, oldest) > oldest)
        continue;
  
      rc = MDBX_NOTFOUND;
      if (flags & MDBX_ALLOC_NEW) {
        rc = MDBX_MAP_FULL;
        if (next <= txn->mt_geo.upper && txn->mt_geo.grow) {
          mdbx_assert(env, next > txn->mt_end_pgno);
          pgno_t aligned = pgno_align2os_pgno(
              env, pgno_add(next, txn->mt_geo.grow - next % txn->mt_geo.grow));
  
          if (aligned > txn->mt_geo.upper)
            aligned = txn->mt_geo.upper;
          mdbx_assert(env, aligned > txn->mt_end_pgno);
  
          mdbx_verbose("try growth datafile to %" PRIaPGNO " pages (+%" PRIaPGNO
                       ")",
                       aligned, aligned - txn->mt_end_pgno);
          rc = mdbx_mapresize_implicit(env, txn->mt_next_pgno, aligned,
                                       txn->mt_geo.upper);
          if (rc == MDBX_SUCCESS) {
            env->me_txn->mt_end_pgno = aligned;
            goto done;
          }
  
          mdbx_error("unable growth datafile to %" PRIaPGNO " pages (+%" PRIaPGNO
                     "), errcode %d",
                     aligned, aligned - txn->mt_end_pgno, rc);
        } else {
          mdbx_debug("gc-alloc: next %u > upper %u", next, txn->mt_geo.upper);
        }
      }
  
    fail:
      mdbx_tassert(txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist,
                                              txn->mt_next_pgno));
      if (likely(mp)) {
        *mp = nullptr;
        txn->mt_flags |= MDBX_TXN_ERROR;
      }
      mdbx_assert(env, rc != MDBX_SUCCESS);
      return rc;
    }
  
  done:
    if (unlikely(mp == nullptr))
      return MDBX_SUCCESS;
    mdbx_ensure(env, pgno >= NUM_METAS);
    if (env->me_flags & MDBX_WRITEMAP) {
      np = pgno2page(env, pgno);
      /* LY: reset no-access flag from mdbx_loose_page() */
      VALGRIND_MAKE_MEM_UNDEFINED(np, pgno2bytes(env, num));
      ASAN_UNPOISON_MEMORY_REGION(np, pgno2bytes(env, num));
    } else {
      if (unlikely(!(np = mdbx_page_malloc(txn, num)))) {
        rc = MDBX_ENOMEM;
        goto fail;
      }
    }
  
    if (range_begin) {
      mdbx_cassert(mc, (mc->mc_flags & C_GCFREEZE) == 0);
      mdbx_tassert(txn, pgno < txn->mt_next_pgno);
      mdbx_tassert(txn, pgno == re_list[range_begin]);
      /* Cutoff allocated pages from tw.reclaimed_pglist */
  #if MDBX_PNL_ASCENDING
      for (unsigned i = range_begin + num; i <= re_len;)
        re_list[range_begin++] = re_list[i++];
      MDBX_PNL_SIZE(re_list) = re_len = range_begin - 1;
  #else
      MDBX_PNL_SIZE(re_list) = re_len -= num;
      for (unsigned i = range_begin - num; i < re_len;)
        re_list[++i] = re_list[++range_begin];
  #endif
      mdbx_tassert(txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist,
                                              txn->mt_next_pgno));
    } else {
      txn->mt_next_pgno = pgno + num;
      mdbx_assert(env, txn->mt_next_pgno <= txn->mt_end_pgno);
    }
  
    if (unlikely(env->me_flags & MDBX_PAGEPERTURB))
      memset(np, -1, pgno2bytes(env, num));
    VALGRIND_MAKE_MEM_UNDEFINED(np, pgno2bytes(env, num));
  
    np->mp_pgno = pgno;
    np->mp_leaf2_ksize = 0;
    np->mp_flags = 0;
    np->mp_pages = num;
    rc = mdbx_page_dirty(txn, np);
    if (unlikely(rc != MDBX_SUCCESS))
      goto fail;
    *mp = np;
  
    mdbx_tassert(
        txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist, txn->mt_next_pgno));
    return MDBX_SUCCESS;
  }
  
  /* Copy the used portions of a non-overflow page. */
  __hot static void mdbx_page_copy(MDBX_page *dst, MDBX_page *src, size_t psize) {
    STATIC_ASSERT(UINT16_MAX > MAX_PAGESIZE - PAGEHDRSZ);
    STATIC_ASSERT(MIN_PAGESIZE > PAGEHDRSZ + NODESIZE * 4);
    if (!IS_LEAF2(src)) {
      size_t upper = src->mp_upper, lower = src->mp_lower, unused = upper - lower;
  
      /* If page isn't full, just copy the used portion. Adjust
       * alignment so memcpy may copy words instead of bytes. */
      if (unused >= MDBX_CACHELINE_SIZE * 2) {
        lower = ceil_powerof2(lower + PAGEHDRSZ, sizeof(void *));
        upper = floor_powerof2(upper + PAGEHDRSZ, sizeof(void *));
        memcpy(dst, src, lower);
        dst = (void *)((char *)dst + upper);
        src = (void *)((char *)src + upper);
        psize -= upper;
      }
    }
    memcpy(dst, src, psize);
  }
  
  /* Pull a page off the txn's spill list, if present.
   *
   * If a page being referenced was spilled to disk in this txn, bring
   * it back and make it dirty/writable again.
   *
   * [in] txn   the transaction handle.
   * [in] mp    the page being referenced. It must not be dirty.
   * [out] ret  the writable page, if any.
   *            ret is unchanged if mp wasn't spilled. */
  static int __must_check_result mdbx_page_unspill(MDBX_txn *txn, MDBX_page *mp,
                                                   MDBX_page **ret) {
    MDBX_env *env = txn->mt_env;
    pgno_t pgno = mp->mp_pgno, pn = pgno << 1;
  
    for (const MDBX_txn *tx2 = txn; tx2; tx2 = tx2->mt_parent) {
      if (!tx2->tw.spill_pages)
        continue;
      unsigned i = mdbx_pnl_exist(tx2->tw.spill_pages, pn);
      if (!i)
        continue;
      if (txn->tw.dirtyroom == 0)
        return MDBX_TXN_FULL;
      unsigned num = IS_OVERFLOW(mp) ? mp->mp_pages : 1;
      MDBX_page *np = mp;
      if ((env->me_flags & MDBX_WRITEMAP) == 0) {
        np = mdbx_page_malloc(txn, num);
        if (unlikely(!np))
          return MDBX_ENOMEM;
        if (unlikely(num > 1))
          memcpy(np, mp, pgno2bytes(env, num));
        else
          mdbx_page_copy(np, mp, env->me_psize);
      }
      mdbx_debug("unspill page %" PRIaPGNO, mp->mp_pgno);
      if (tx2 == txn) {
        /* If in current txn, this page is no longer spilled.
         * If it happens to be the last page, truncate the spill list.
         * Otherwise mark it as deleted by setting the LSB. */
        txn->tw.spill_pages[i] |= 1;
        if (i == MDBX_PNL_SIZE(txn->tw.spill_pages))
          MDBX_PNL_SIZE(txn->tw.spill_pages) -= 1;
      } /* otherwise, if belonging to a parent txn, the
         * page remains spilled until child commits */
  
      int rc = mdbx_page_dirty(txn, np);
      if (likely(rc == MDBX_SUCCESS))
        *ret = np;
      return rc;
    }
    return MDBX_SUCCESS;
  }
  
  /* Touch a page: make it dirty and re-insert into tree with updated pgno.
   * Set MDBX_TXN_ERROR on failure.
   *
   * [in] mc  cursor pointing to the page to be touched
   *
   * Returns 0 on success, non-zero on failure. */
  __hot static int mdbx_page_touch(MDBX_cursor *mc) {
    MDBX_page *mp = mc->mc_pg[mc->mc_top], *np;
    MDBX_txn *txn = mc->mc_txn;
    MDBX_cursor *m2, *m3;
    pgno_t pgno;
    int rc;
  
    mdbx_cassert(mc, !IS_OVERFLOW(mp));
    if (!F_ISSET(mp->mp_flags, P_DIRTY)) {
      if (txn->mt_flags & MDBX_TXN_SPILLS) {
        np = NULL;
        rc = mdbx_page_unspill(txn, mp, &np);
        if (unlikely(rc))
          goto fail;
        if (likely(np))
          goto done;
      }
  
      if (unlikely((rc = mdbx_pnl_need(&txn->tw.retired_pages, 1)) ||
                   (rc = mdbx_page_alloc(mc, 1, &np, MDBX_ALLOC_ALL))))
        goto fail;
      pgno = np->mp_pgno;
      mdbx_debug("touched db %d page %" PRIaPGNO " -> %" PRIaPGNO, DDBI(mc),
                 mp->mp_pgno, pgno);
      mdbx_cassert(mc, mp->mp_pgno != pgno);
      mdbx_pnl_xappend(txn->tw.retired_pages, mp->mp_pgno);
      mdbx_tassert(txn, mdbx_dpl_find(txn->tw.dirtylist, mp->mp_pgno) == nullptr);
      /* Update the parent page, if any, to point to the new page */
      if (mc->mc_top) {
        MDBX_page *parent = mc->mc_pg[mc->mc_top - 1];
        MDBX_node *node = page_node(parent, mc->mc_ki[mc->mc_top - 1]);
        node_set_pgno(node, pgno);
      } else {
        mc->mc_db->md_root = pgno;
      }
    } else if (txn->mt_parent && !IS_SUBP(mp)) {
      mdbx_tassert(txn, (txn->mt_env->me_flags & MDBX_WRITEMAP) == 0);
      pgno = mp->mp_pgno;
      /* If txn has a parent, make sure the page is in our dirty list. */
      const MDBX_page *const dp = mdbx_dpl_find(txn->tw.dirtylist, pgno);
      if (dp) {
        if (unlikely(mp != dp)) { /* bad cursor? */
          mdbx_error("wrong page 0x%p #%" PRIaPGNO
                     " in the dirtylist, expecting %p",
                     __Wpedantic_format_voidptr(dp), pgno,
                     __Wpedantic_format_voidptr(mp));
          mc->mc_flags &= ~(C_INITIALIZED | C_EOF);
          rc = MDBX_PROBLEM;
          goto fail;
        }
        return MDBX_SUCCESS;
      }
  
      mdbx_debug("clone db %d page %" PRIaPGNO, DDBI(mc), mp->mp_pgno);
      mdbx_cassert(mc, txn->tw.dirtylist->length <= MDBX_DPL_TXNFULL);
      /* No - copy it */
      np = mdbx_page_malloc(txn, 1);
      if (unlikely(!np)) {
        rc = MDBX_ENOMEM;
        goto fail;
      }
      rc = mdbx_dpl_append(txn->tw.dirtylist, pgno, np);
      if (unlikely(rc)) {
        mdbx_dpage_free(txn->mt_env, np, 1);
        goto fail;
      }
    } else {
      return MDBX_SUCCESS;
    }
  
    mdbx_page_copy(np, mp, txn->mt_env->me_psize);
    np->mp_pgno = pgno;
    np->mp_txnid = INVALID_TXNID;
    np->mp_flags |= P_DIRTY;
  
  done:
    /* Adjust cursors pointing to mp */
    mc->mc_pg[mc->mc_top] = np;
    m2 = txn->tw.cursors[mc->mc_dbi];
    if (mc->mc_flags & C_SUB) {
      for (; m2; m2 = m2->mc_next) {
        m3 = &m2->mc_xcursor->mx_cursor;
        if (m3->mc_snum < mc->mc_snum)
          continue;
        if (m3->mc_pg[mc->mc_top] == mp)
          m3->mc_pg[mc->mc_top] = np;
      }
    } else {
      for (; m2; m2 = m2->mc_next) {
        if (m2->mc_snum < mc->mc_snum)
          continue;
        if (m2 == mc)
          continue;
        if (m2->mc_pg[mc->mc_top] == mp) {
          m2->mc_pg[mc->mc_top] = np;
          if (XCURSOR_INITED(m2) && IS_LEAF(np))
            XCURSOR_REFRESH(m2, np, m2->mc_ki[mc->mc_top]);
        }
      }
    }
    return MDBX_SUCCESS;
  
  fail:
    txn->mt_flags |= MDBX_TXN_ERROR;
    return rc;
  }
  
  __cold static int mdbx_env_sync_internal(MDBX_env *env, bool force,
                                           bool nonblock) {
    unsigned flags = env->me_flags & ~MDBX_NOMETASYNC;
    if (unlikely(flags & (MDBX_RDONLY | MDBX_FATAL_ERROR)))
      return MDBX_EACCESS;
  
    if (unlikely(!env->me_map))
      return MDBX_EPERM;
  
    int rc = MDBX_RESULT_TRUE /* means "nothing to sync" */;
    bool need_unlock = false;
    if (nonblock && *env->me_unsynced_pages == 0)
      goto fastpath;
  
    const bool outside_txn = (env->me_txn0->mt_owner != mdbx_thread_self());
    if (outside_txn) {
      int err = mdbx_txn_lock(env, nonblock);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
      need_unlock = true;
    }
  
    const MDBX_meta *head = mdbx_meta_head(env);
    pgno_t unsynced_pages = *env->me_unsynced_pages;
    if (!META_IS_STEADY(head) || unsynced_pages) {
      const pgno_t autosync_threshold = *env->me_autosync_threshold;
      const uint64_t autosync_period = *env->me_autosync_period;
      if (force || (autosync_threshold && unsynced_pages >= autosync_threshold) ||
          (autosync_period &&
           mdbx_osal_monotime() - *env->me_sync_timestamp >= autosync_period))
        flags &= MDBX_WRITEMAP /* clear flags for full steady sync */;
  
      if (outside_txn) {
        if (unsynced_pages > /* FIXME: define threshold */ 16 &&
            (flags & MDBX_SAFE_NOSYNC) == 0) {
          mdbx_assert(env, ((flags ^ env->me_flags) & MDBX_WRITEMAP) == 0);
          const size_t usedbytes = pgno_align2os_bytes(env, head->mm_geo.next);
  
          mdbx_txn_unlock(env);
  
          /* LY: pre-sync without holding lock to reduce latency for writer(s) */
          int err = (flags & MDBX_WRITEMAP)
                        ? mdbx_msync(&env->me_dxb_mmap, 0, usedbytes, false)
                        : mdbx_fsync(env->me_lazy_fd, MDBX_SYNC_DATA);
          if (unlikely(err != MDBX_SUCCESS))
            return err;
  
          err = mdbx_txn_lock(env, nonblock);
          if (unlikely(err != MDBX_SUCCESS))
            return err;
  
          /* LY: head and unsynced_pages may be changed. */
          head = mdbx_meta_head(env);
          unsynced_pages = *env->me_unsynced_pages;
        }
        env->me_txn0->mt_txnid = meta_txnid(env, head, false);
        mdbx_find_oldest(env->me_txn0);
        rc = MDBX_RESULT_FALSE /* means "some data was synced" */;
      }
  
      if (!META_IS_STEADY(head) ||
          ((flags & MDBX_SAFE_NOSYNC) == 0 && unsynced_pages)) {
        mdbx_debug("meta-head %" PRIaPGNO ", %s, sync_pending %" PRIaPGNO,
                   data_page(head)->mp_pgno, mdbx_durable_str(head),
                   unsynced_pages);
        MDBX_meta meta = *head;
        int err = mdbx_sync_locked(env, flags | MDBX_SHRINK_ALLOWED, &meta);
        if (unlikely(err != MDBX_SUCCESS)) {
          if (need_unlock)
            mdbx_txn_unlock(env);
          return err;
        }
        rc = MDBX_RESULT_FALSE /* means "some data was synced" */;
      }
    }
  
  fastpath:
    /* LY: sync meta-pages if MDBX_NOMETASYNC enabled
     *     and someone was not synced above. */
    if (rc == MDBX_RESULT_TRUE && (env->me_flags & MDBX_NOMETASYNC) != 0) {
      const txnid_t head_txnid = mdbx_recent_committed_txnid(env);
      if (*env->me_meta_sync_txnid != (uint32_t)head_txnid) {
        rc = (flags & MDBX_WRITEMAP)
                 ? mdbx_msync(&env->me_dxb_mmap, 0,
                              pgno_align2os_bytes(env, NUM_METAS), false)
                 : mdbx_fsync(env->me_lazy_fd, MDBX_SYNC_DATA | MDBX_SYNC_IODQ);
        if (likely(rc == MDBX_SUCCESS))
          *env->me_meta_sync_txnid = (uint32_t)head_txnid;
      }
    }
    if (need_unlock)
      mdbx_txn_unlock(env);
    return rc;
  }
  
  static __inline int check_env(const MDBX_env *env) {
    if (unlikely(!env))
      return MDBX_EINVAL;
  
    if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
      return MDBX_EBADSIGN;
  
  #if MDBX_ENV_CHECKPID
    if (unlikely(env->me_pid != mdbx_getpid())) {
      ((MDBX_env *)env)->me_flags |= MDBX_FATAL_ERROR;
      return MDBX_PANIC;
    }
  #endif /* MDBX_ENV_CHECKPID */
  
    if (unlikely(env->me_flags & MDBX_FATAL_ERROR))
      return MDBX_PANIC;
  
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_env_sync_ex(MDBX_env *env, bool force, bool nonblock) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    return mdbx_env_sync_internal(env, force, nonblock);
  }
  
  __cold int mdbx_env_sync(MDBX_env *env) { return __inline_mdbx_env_sync(env); }
  
  __cold int mdbx_env_sync_poll(MDBX_env *env) {
    return __inline_mdbx_env_sync_poll(env);
  }
  
  /* Back up parent txn's cursors, then grab the originals for tracking */
  static int mdbx_cursor_shadow(MDBX_txn *parent, MDBX_txn *nested) {
    for (int i = parent->mt_numdbs; --i >= 0;) {
      nested->tw.cursors[i] = NULL;
      MDBX_cursor *mc = parent->tw.cursors[i];
      if (mc != NULL) {
        size_t size = mc->mc_xcursor ? sizeof(MDBX_cursor) + sizeof(MDBX_xcursor)
                                     : sizeof(MDBX_cursor);
        for (MDBX_cursor *bk; mc; mc = bk->mc_next) {
          bk = mc;
          if (mc->mc_signature != MDBX_MC_LIVE)
            continue;
          bk = mdbx_malloc(size);
          if (unlikely(!bk))
            return MDBX_ENOMEM;
          *bk = *mc;
          mc->mc_backup = bk;
          /* Kill pointers into src to reduce abuse: The
           * user may not use mc until dst ends. But we need a valid
           * txn pointer here for cursor fixups to keep working. */
          mc->mc_txn = nested;
          mc->mc_db = &nested->mt_dbs[i];
          mc->mc_dbistate = &nested->mt_dbistate[i];
          MDBX_xcursor *mx = mc->mc_xcursor;
          if (mx != NULL) {
            *(MDBX_xcursor *)(bk + 1) = *mx;
            mx->mx_cursor.mc_txn = nested;
          }
          mc->mc_next = nested->tw.cursors[i];
          nested->tw.cursors[i] = mc;
        }
      }
    }
    return MDBX_SUCCESS;
  }
  
  /* Close this write txn's cursors, give parent txn's cursors back to parent.
   *
   * [in] txn     the transaction handle.
   * [in] merge   true to keep changes to parent cursors, false to revert.
   *
   * Returns 0 on success, non-zero on failure. */
  static void mdbx_cursors_eot(MDBX_txn *txn, const bool merge) {
    mdbx_tassert(txn, (txn->mt_flags & MDBX_TXN_RDONLY) == 0);
    for (int i = txn->mt_numdbs; --i >= 0;) {
      MDBX_cursor *next, *mc = txn->tw.cursors[i];
      if (!mc)
        continue;
      txn->tw.cursors[i] = NULL;
      do {
        const unsigned stage = mc->mc_signature;
        MDBX_cursor *bk = mc->mc_backup;
        next = mc->mc_next;
        mdbx_ensure(txn->mt_env,
                    stage == MDBX_MC_LIVE || (stage == MDBX_MC_WAIT4EOT && bk));
        mdbx_cassert(mc, mc->mc_dbi == (unsigned)i);
        if (bk) {
          MDBX_xcursor *mx = mc->mc_xcursor;
          mdbx_cassert(mc, mx == bk->mc_xcursor);
          mdbx_tassert(txn, txn->mt_parent != NULL);
          mdbx_ensure(txn->mt_env, bk->mc_signature == MDBX_MC_LIVE);
          if (stage == MDBX_MC_WAIT4EOT /* Cursor was closed by user */)
            mc->mc_signature = stage /* Promote closed state to parent txn */;
          else if (merge) {
            /* Preserve changes from nested to parent txn */
            mc->mc_next = bk->mc_next;
            mc->mc_backup = bk->mc_backup;
            mc->mc_txn = bk->mc_txn;
            *bk->mc_db = *mc->mc_db;
            mc->mc_db = bk->mc_db;
            *bk->mc_dbistate = *mc->mc_dbistate;
            mc->mc_dbistate = bk->mc_dbistate;
            if (mx) {
              if (mx != bk->mc_xcursor) {
                *bk->mc_xcursor = *mx;
                mx = bk->mc_xcursor;
              }
              mx->mx_cursor.mc_txn = bk->mc_txn;
            }
          } else {
            /* Restore from backup, i.e. rollback/abort nested txn */
            *mc = *bk;
            if (mx)
              *mx = *(MDBX_xcursor *)(bk + 1);
          }
          bk->mc_signature = 0;
          mdbx_free(bk);
        } else {
          mdbx_ensure(txn->mt_env, stage == MDBX_MC_LIVE);
          mc->mc_signature = MDBX_MC_READY4CLOSE /* Cursor may be reused */;
          mc->mc_flags = 0 /* reset C_UNTRACK */;
        }
      } while ((mc = next) != NULL);
    }
  }
  
  #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
  /* Find largest mvcc-snapshot still referenced by this process. */
  static pgno_t mdbx_find_largest_this(MDBX_env *env, pgno_t largest) {
    MDBX_lockinfo *const lck = env->me_lck;
    if (likely(lck != NULL /* exclusive mode */)) {
      const unsigned snap_nreaders = lck->mti_numreaders;
      for (unsigned i = 0; i < snap_nreaders; ++i) {
      retry:
        if (lck->mti_readers[i].mr_pid == env->me_pid) {
          /* mdbx_jitter4testing(true); */
          const pgno_t snap_pages = lck->mti_readers[i].mr_snapshot_pages_used;
          const txnid_t snap_txnid = safe64_read(&lck->mti_readers[i].mr_txnid);
          mdbx_memory_barrier();
          if (unlikely(snap_pages != lck->mti_readers[i].mr_snapshot_pages_used ||
                       snap_txnid != safe64_read(&lck->mti_readers[i].mr_txnid)))
            goto retry;
          if (largest < snap_pages &&
              lck->mti_oldest_reader <= /* ignore pending updates */ snap_txnid &&
              snap_txnid <= MAX_TXNID)
            largest = snap_pages;
        }
      }
    }
    return largest;
  }
  
  static void mdbx_txn_valgrind(MDBX_env *env, MDBX_txn *txn) {
  #if !defined(__SANITIZE_ADDRESS__)
    if (!RUNNING_ON_VALGRIND)
      return;
  #endif
  
    if (txn) { /* transaction start */
      if (env->me_poison_edge < txn->mt_next_pgno)
        env->me_poison_edge = txn->mt_next_pgno;
      VALGRIND_MAKE_MEM_DEFINED(env->me_map, pgno2bytes(env, txn->mt_next_pgno));
      ASAN_UNPOISON_MEMORY_REGION(env->me_map,
                                  pgno2bytes(env, txn->mt_next_pgno));
      /* don't touch more, it should be already poisoned */
    } else { /* transaction end */
      bool should_unlock = false;
      pgno_t last = MAX_PAGENO;
      if (env->me_txn0 && env->me_txn0->mt_owner == mdbx_thread_self()) {
        /* inside write-txn */
        MDBX_meta *head = mdbx_meta_head(env);
        last = head->mm_geo.next;
      } else if (env->me_flags & MDBX_RDONLY) {
        /* read-only mode, no write-txn, no wlock mutex */
        last = NUM_METAS;
      } else if (mdbx_txn_lock(env, true) == MDBX_SUCCESS) {
        /* no write-txn */
        last = NUM_METAS;
        should_unlock = true;
      } else {
        /* write txn is running, therefore shouldn't poison any memory range */
        return;
      }
  
      last = mdbx_find_largest_this(env, last);
      const pgno_t edge = env->me_poison_edge;
      if (edge > last) {
        mdbx_assert(env, last >= NUM_METAS);
        env->me_poison_edge = last;
        VALGRIND_MAKE_MEM_NOACCESS(env->me_map + pgno2bytes(env, last),
                                   pgno2bytes(env, edge - last));
        ASAN_POISON_MEMORY_REGION(env->me_map + pgno2bytes(env, last),
                                  pgno2bytes(env, edge - last));
      }
      if (should_unlock)
        mdbx_txn_unlock(env);
    }
  }
  #endif /* MDBX_USE_VALGRIND || __SANITIZE_ADDRESS__ */
  
  typedef struct {
    int err;
    MDBX_reader *rslot;
  } bind_rslot_result;
  
  static bind_rslot_result bind_rslot(MDBX_env *env, const uintptr_t tid) {
    mdbx_assert(env, env->me_lck);
    mdbx_assert(env, env->me_lck->mti_magic_and_version == MDBX_LOCK_MAGIC);
    mdbx_assert(env, env->me_lck->mti_os_and_format == MDBX_LOCK_FORMAT);
  
    bind_rslot_result result = {mdbx_rdt_lock(env), nullptr};
    if (unlikely(MDBX_IS_ERROR(result.err)))
      return result;
    if (unlikely(env->me_flags & MDBX_FATAL_ERROR)) {
      mdbx_rdt_unlock(env);
      result.err = MDBX_PANIC;
      return result;
    }
    if (unlikely(!env->me_map)) {
      mdbx_rdt_unlock(env);
      result.err = MDBX_EPERM;
      return result;
    }
  
    if (unlikely(env->me_live_reader != env->me_pid)) {
      result.err = mdbx_rpid_set(env);
      if (unlikely(result.err != MDBX_SUCCESS)) {
        mdbx_rdt_unlock(env);
        return result;
      }
      env->me_live_reader = env->me_pid;
    }
  
    result.err = MDBX_SUCCESS;
    unsigned slot, nreaders;
    while (1) {
      nreaders = env->me_lck->mti_numreaders;
      for (slot = 0; slot < nreaders; slot++)
        if (env->me_lck->mti_readers[slot].mr_pid == 0)
          break;
  
      if (likely(slot < env->me_maxreaders))
        break;
  
      result.err = mdbx_cleanup_dead_readers(env, true, NULL);
      if (result.err != MDBX_RESULT_TRUE) {
        mdbx_rdt_unlock(env);
        result.err =
            (result.err == MDBX_SUCCESS) ? MDBX_READERS_FULL : result.err;
        return result;
      }
    }
  
    result.rslot = &env->me_lck->mti_readers[slot];
    /* Claim the reader slot, carefully since other code
     * uses the reader table un-mutexed: First reset the
     * slot, next publish it in lck->mti_numreaders.  After
     * that, it is safe for mdbx_env_close() to touch it.
     * When it will be closed, we can finally claim it. */
    result.rslot->mr_pid = 0;
    safe64_reset(&result.rslot->mr_txnid, true);
    if (slot == nreaders)
      env->me_lck->mti_numreaders = ++nreaders;
    result.rslot->mr_tid = (env->me_flags & MDBX_NOTLS) ? 0 : tid;
    result.rslot->mr_pid = env->me_pid;
    mdbx_rdt_unlock(env);
  
    if (likely(env->me_flags & MDBX_ENV_TXKEY)) {
      mdbx_assert(env, env->me_live_reader == env->me_pid);
      thread_rthc_set(env->me_txkey, result.rslot);
    }
    return result;
  }
  
  __cold int mdbx_thread_register(const MDBX_env *env) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!env->me_lck))
      return (env->me_flags & MDBX_EXCLUSIVE) ? MDBX_EINVAL : MDBX_EPERM;
  
    if (unlikely((env->me_flags & MDBX_ENV_TXKEY) == 0)) {
      mdbx_assert(env, !env->me_lck || (env->me_flags & MDBX_NOTLS));
      return MDBX_EINVAL /* MDBX_NOTLS mode */;
    }
  
    mdbx_assert(env, (env->me_flags & (MDBX_NOTLS | MDBX_ENV_TXKEY |
                                       MDBX_EXCLUSIVE)) == MDBX_ENV_TXKEY);
    MDBX_reader *r = thread_rthc_get(env->me_txkey);
    if (unlikely(r != NULL)) {
      mdbx_assert(env, r->mr_pid == env->me_pid);
      mdbx_assert(env, r->mr_tid == mdbx_thread_self());
      if (unlikely(r->mr_pid != env->me_pid))
        return MDBX_BAD_RSLOT;
      return MDBX_RESULT_TRUE /* already registered */;
    }
  
    const uintptr_t tid = mdbx_thread_self();
    if (env->me_txn0 && unlikely(env->me_txn0->mt_owner == tid))
      return MDBX_TXN_OVERLAPPING;
    return bind_rslot((MDBX_env *)env, tid).err;
  }
  
  __cold int mdbx_thread_unregister(const MDBX_env *env) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!env->me_lck))
      return MDBX_RESULT_TRUE;
  
    if (unlikely((env->me_flags & MDBX_ENV_TXKEY) == 0)) {
      mdbx_assert(env, !env->me_lck || (env->me_flags & MDBX_NOTLS));
      return MDBX_RESULT_TRUE /* MDBX_NOTLS mode */;
    }
  
    mdbx_assert(env, (env->me_flags & (MDBX_NOTLS | MDBX_ENV_TXKEY |
                                       MDBX_EXCLUSIVE)) == MDBX_ENV_TXKEY);
    MDBX_reader *r = thread_rthc_get(env->me_txkey);
    if (unlikely(r == NULL))
      return MDBX_RESULT_TRUE /* not registered */;
  
    mdbx_assert(env, r->mr_pid == env->me_pid);
    mdbx_assert(env, r->mr_tid == mdbx_thread_self());
    if (unlikely(r->mr_pid != env->me_pid || r->mr_tid != mdbx_thread_self()))
      return MDBX_BAD_RSLOT;
  
    if (unlikely(r->mr_txnid.inconsistent < SAFE64_INVALID_THRESHOLD))
      return MDBX_BUSY /* transaction is still active */;
  
    r->mr_pid = 0;
    mdbx_compiler_barrier();
    env->me_lck->mti_readers_refresh_flag = true;
    thread_rthc_set(env->me_txkey, nullptr);
    return MDBX_SUCCESS;
  }
  
  /* Common code for mdbx_txn_begin() and mdbx_txn_renew(). */
  static int mdbx_txn_renew0(MDBX_txn *txn, const unsigned flags) {
    MDBX_env *env = txn->mt_env;
    int rc;
  
  #if MDBX_ENV_CHECKPID
    if (unlikely(env->me_pid != mdbx_getpid())) {
      env->me_flags |= MDBX_FATAL_ERROR;
      return MDBX_PANIC;
    }
  #endif /* MDBX_ENV_CHECKPID */
  
    STATIC_ASSERT(sizeof(MDBX_reader) == 32);
  #if MDBX_LOCKING > 0
    STATIC_ASSERT(offsetof(MDBX_lockinfo, mti_wlock) % MDBX_CACHELINE_SIZE == 0);
    STATIC_ASSERT(offsetof(MDBX_lockinfo, mti_rlock) % MDBX_CACHELINE_SIZE == 0);
  #else
    STATIC_ASSERT(
        offsetof(MDBX_lockinfo, mti_oldest_reader) % MDBX_CACHELINE_SIZE == 0);
    STATIC_ASSERT(offsetof(MDBX_lockinfo, mti_numreaders) % MDBX_CACHELINE_SIZE ==
                  0);
  #endif /* MDBX_LOCKING */
    STATIC_ASSERT(offsetof(MDBX_lockinfo, mti_readers) % MDBX_CACHELINE_SIZE ==
                  0);
  
    const uintptr_t tid = mdbx_thread_self();
    if (flags & MDBX_TXN_RDONLY) {
      mdbx_assert(env, (flags & ~(MDBX_TXN_RO_BEGIN_FLAGS | MDBX_WRITEMAP)) == 0);
      txn->mt_flags =
          MDBX_TXN_RDONLY | (env->me_flags & (MDBX_NOTLS | MDBX_WRITEMAP));
      MDBX_reader *r = txn->to.reader;
      STATIC_ASSERT(sizeof(uintptr_t) == sizeof(r->mr_tid));
      if (likely(env->me_flags & MDBX_ENV_TXKEY)) {
        mdbx_assert(env, !(env->me_flags & MDBX_NOTLS));
        r = thread_rthc_get(env->me_txkey);
        if (likely(r)) {
          if (unlikely(!r->mr_pid) &&
              (mdbx_runtime_flags & MDBX_DBG_LEGACY_MULTIOPEN)) {
            thread_rthc_set(env->me_txkey, nullptr);
            r = nullptr;
          } else {
            mdbx_assert(env, r->mr_pid == env->me_pid);
            mdbx_assert(env, r->mr_tid == mdbx_thread_self());
          }
        }
      } else {
        mdbx_assert(env, !env->me_lck || (env->me_flags & MDBX_NOTLS));
      }
  
      if (likely(r)) {
        if (unlikely(r->mr_pid != env->me_pid ||
                     r->mr_txnid.inconsistent < SAFE64_INVALID_THRESHOLD))
          return MDBX_BAD_RSLOT;
      } else if (env->me_lck) {
        bind_rslot_result brs = bind_rslot(env, tid);
        if (unlikely(brs.err != MDBX_SUCCESS))
          return brs.err;
        r = brs.rslot;
      }
      txn->to.reader = r;
      if (flags & (MDBX_TXN_RDONLY_PREPARE - MDBX_TXN_RDONLY)) {
        mdbx_assert(env, txn->mt_txnid == 0);
        mdbx_assert(env, txn->mt_owner == 0);
        mdbx_assert(env, txn->mt_numdbs == 0);
        if (likely(r)) {
          mdbx_assert(env, r->mr_snapshot_pages_used == 0);
          mdbx_assert(env, r->mr_txnid.inconsistent >= SAFE64_INVALID_THRESHOLD);
          r->mr_snapshot_pages_used = 0;
        }
        txn->mt_flags = MDBX_TXN_RDONLY | MDBX_TXN_FINISHED;
        return MDBX_SUCCESS;
      }
  
      /* Seek & fetch the last meta */
      if (likely(/* not recovery mode */ env->me_stuck_meta < 0)) {
        while (1) {
          MDBX_meta *const meta = mdbx_meta_head(env);
          mdbx_jitter4testing(false);
          const txnid_t snap = mdbx_meta_txnid_fluid(env, meta);
          mdbx_jitter4testing(false);
          if (likely(r)) {
            safe64_reset(&r->mr_txnid, false);
            r->mr_snapshot_pages_used = meta->mm_geo.next;
            r->mr_snapshot_pages_retired = meta->mm_pages_retired;
            safe64_write(&r->mr_txnid, snap);
            mdbx_jitter4testing(false);
            mdbx_assert(env, r->mr_pid == mdbx_getpid());
            mdbx_assert(
                env, r->mr_tid ==
                         ((env->me_flags & MDBX_NOTLS) ? 0 : mdbx_thread_self()));
            mdbx_assert(env, r->mr_txnid.inconsistent == snap);
            mdbx_compiler_barrier();
            env->me_lck->mti_readers_refresh_flag = true;
            mdbx_flush_incoherent_cpu_writeback();
          }
          mdbx_jitter4testing(true);
  
          /* Snap the state from current meta-head */
          txn->mt_txnid = snap;
          txn->mt_geo = meta->mm_geo;
          memcpy(txn->mt_dbs, meta->mm_dbs, CORE_DBS * sizeof(MDBX_db));
          txn->mt_canary = meta->mm_canary;
  
          /* LY: Retry on a race, ITS#7970. */
          mdbx_compiler_barrier();
          if (likely(meta == mdbx_meta_head(env) &&
                     snap == mdbx_meta_txnid_fluid(env, meta) &&
                     snap >= *env->me_oldest)) {
            mdbx_jitter4testing(false);
            break;
          }
        }
      } else {
        /* recovery mode */
        MDBX_meta *const meta = METAPAGE(env, env->me_stuck_meta);
        txn->mt_txnid = mdbx_meta_txnid_stable(env, meta);
        txn->mt_geo = meta->mm_geo;
        memcpy(txn->mt_dbs, meta->mm_dbs, CORE_DBS * sizeof(MDBX_db));
        txn->mt_canary = meta->mm_canary;
        if (likely(r)) {
          r->mr_snapshot_pages_used = meta->mm_geo.next;
          r->mr_snapshot_pages_retired = meta->mm_pages_retired;
          r->mr_txnid.inconsistent = txn->mt_txnid;
          mdbx_jitter4testing(false);
          mdbx_assert(env, r->mr_pid == mdbx_getpid());
          mdbx_assert(
              env, r->mr_tid ==
                       ((env->me_flags & MDBX_NOTLS) ? 0 : mdbx_thread_self()));
          mdbx_assert(env, r->mr_txnid.inconsistent == txn->mt_txnid);
          mdbx_compiler_barrier();
          env->me_lck->mti_readers_refresh_flag = true;
          mdbx_flush_incoherent_cpu_writeback();
        }
      }
  
      if (unlikely(txn->mt_txnid < MIN_TXNID || txn->mt_txnid > MAX_TXNID)) {
        mdbx_error("%s", "environment corrupted by died writer, must shutdown!");
        rc = MDBX_CORRUPTED;
        goto bailout;
      }
      mdbx_assert(env, txn->mt_txnid >= *env->me_oldest);
      txn->mt_dbxs = env->me_dbxs; /* mostly static anyway */
      mdbx_ensure(env, txn->mt_txnid >=
                           /* paranoia is appropriate here */ *env->me_oldest);
      txn->mt_numdbs = env->me_numdbs;
    } else {
      mdbx_assert(env, (flags & ~(MDBX_TXN_RW_BEGIN_FLAGS | MDBX_TXN_SPILLS |
                                  MDBX_WRITEMAP)) == 0);
      if (unlikely(txn->mt_owner == tid ||
                   /* not recovery mode */ env->me_stuck_meta >= 0))
        return MDBX_BUSY;
      MDBX_lockinfo *const lck = env->me_lck;
      if (lck && (env->me_flags & MDBX_NOTLS) == 0 &&
          (mdbx_runtime_flags & MDBX_DBG_LEGACY_OVERLAP) == 0) {
        const unsigned snap_nreaders = lck->mti_numreaders;
        for (unsigned i = 0; i < snap_nreaders; ++i) {
          if (lck->mti_readers[i].mr_pid == env->me_pid &&
              unlikely(lck->mti_readers[i].mr_tid == tid)) {
            const txnid_t txnid = safe64_read(&lck->mti_readers[i].mr_txnid);
            if (txnid >= MIN_TXNID && txnid <= MAX_TXNID)
              return MDBX_TXN_OVERLAPPING;
          }
        }
      }
  
      /* Not yet touching txn == env->me_txn0, it may be active */
      mdbx_jitter4testing(false);
      rc = mdbx_txn_lock(env, F_ISSET(flags, MDBX_TXN_TRY));
      if (unlikely(rc))
        return rc;
      if (unlikely(env->me_flags & MDBX_FATAL_ERROR)) {
        mdbx_txn_unlock(env);
        return MDBX_PANIC;
      }
  #if defined(_WIN32) || defined(_WIN64)
      if (unlikely(!env->me_map)) {
        mdbx_txn_unlock(env);
        return MDBX_EPERM;
      }
  #endif /* Windows */
  
      mdbx_jitter4testing(false);
      MDBX_meta *meta = mdbx_meta_head(env);
      mdbx_jitter4testing(false);
      txn->mt_canary = meta->mm_canary;
      const txnid_t snap = mdbx_meta_txnid_stable(env, meta);
      txn->mt_txnid = safe64_txnid_next(snap);
      if (unlikely(txn->mt_txnid > MAX_TXNID)) {
        mdbx_error("%s", "txnid overflow!");
        rc = MDBX_TXN_FULL;
        goto bailout;
      }
  
      txn->mt_flags = flags;
      txn->mt_child = NULL;
      txn->tw.loose_pages = NULL;
      txn->tw.loose_count = 0;
      txn->tw.dirtyroom = MDBX_DPL_TXNFULL;
      txn->tw.dirtylist = env->me_dirtylist;
      mdbx_dpl_clear(txn->tw.dirtylist);
      MDBX_PNL_SIZE(txn->tw.retired_pages) = 0;
      txn->tw.spill_pages = NULL;
      txn->tw.last_reclaimed = 0;
      if (txn->tw.lifo_reclaimed)
        MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) = 0;
      env->me_txn = txn;
      txn->mt_numdbs = env->me_numdbs;
      memcpy(txn->mt_dbiseqs, env->me_dbiseqs, txn->mt_numdbs * sizeof(unsigned));
      /* Copy the DB info and flags */
      memcpy(txn->mt_dbs, meta->mm_dbs, CORE_DBS * sizeof(MDBX_db));
      /* Moved to here to avoid a data race in read TXNs */
      txn->mt_geo = meta->mm_geo;
      txn->tw.loose_refund_wl = txn->mt_next_pgno;
    }
  
    /* Setup db info */
    mdbx_compiler_barrier();
    for (unsigned i = CORE_DBS; i < txn->mt_numdbs; i++) {
      const unsigned db_flags = env->me_dbflags[i];
      txn->mt_dbs[i].md_flags = db_flags & DB_PERSISTENT_FLAGS;
      txn->mt_dbistate[i] =
          (db_flags & DB_VALID) ? DBI_VALID | DBI_USRVALID | DBI_STALE : 0;
    }
    txn->mt_dbistate[MAIN_DBI] = DBI_VALID | DBI_USRVALID;
    txn->mt_dbistate[FREE_DBI] = DBI_VALID;
  
    if (unlikely(env->me_flags & MDBX_FATAL_ERROR)) {
      mdbx_warning("%s", "environment had fatal error, must shutdown!");
      rc = MDBX_PANIC;
    } else {
      const size_t size =
          pgno2bytes(env, (txn->mt_flags & MDBX_TXN_RDONLY) ? txn->mt_next_pgno
                                                            : txn->mt_end_pgno);
      if (unlikely(size > env->me_dxb_mmap.limit)) {
        if (txn->mt_geo.upper > MAX_PAGENO ||
            bytes2pgno(env, pgno2bytes(env, txn->mt_geo.upper)) !=
                txn->mt_geo.upper) {
          rc = MDBX_UNABLE_EXTEND_MAPSIZE;
          goto bailout;
        }
        rc = mdbx_mapresize(env, txn->mt_next_pgno, txn->mt_end_pgno,
                            txn->mt_geo.upper,
                            (txn->mt_flags & MDBX_TXN_RDONLY) ? true : false);
        if (rc != MDBX_SUCCESS)
          goto bailout;
      }
      if (txn->mt_flags & MDBX_TXN_RDONLY) {
  #if defined(_WIN32) || defined(_WIN64)
        if ((size > env->me_dbgeo.lower && env->me_dbgeo.shrink) ||
            (mdbx_RunningUnderWine() &&
             /* under Wine acquisition of remap_guard is always required,
              * since Wine don't support section extending,
              * i.e. in both cases unmap+map are required. */
             size < env->me_dbgeo.upper && env->me_dbgeo.grow)) {
          txn->mt_flags |= MDBX_SHRINK_ALLOWED;
          mdbx_srwlock_AcquireShared(&env->me_remap_guard);
        }
  #endif /* Windows */
      } else {
        env->me_dxb_mmap.current = size;
  #if defined(_WIN32) || defined(_WIN64)
        env->me_dxb_mmap.filesize =
            (env->me_dxb_mmap.filesize < size) ? size : env->me_dxb_mmap.filesize;
  #endif /* Windows */
      }
  #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
      mdbx_txn_valgrind(env, txn);
  #endif
      txn->mt_owner = tid;
      return MDBX_SUCCESS;
    }
  bailout:
    mdbx_tassert(txn, rc != MDBX_SUCCESS);
    mdbx_txn_end(txn, MDBX_END_SLOT | MDBX_END_FAIL_BEGIN);
    return rc;
  }
  
  static __always_inline int check_txn(const MDBX_txn *txn, int bad_bits) {
    if (unlikely(!txn))
      return MDBX_EINVAL;
  
    if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
      return MDBX_EBADSIGN;
  
    if (unlikely(txn->mt_flags & bad_bits))
      return MDBX_BAD_TXN;
  
  #if MDBX_TXN_CHECKOWNER
    if ((txn->mt_flags & MDBX_NOTLS) == 0 &&
        unlikely(txn->mt_owner != mdbx_thread_self()))
      return txn->mt_owner ? MDBX_THREAD_MISMATCH : MDBX_BAD_TXN;
  #endif /* MDBX_TXN_CHECKOWNER */
  
    return MDBX_SUCCESS;
  }
  
  static __always_inline int check_txn_rw(const MDBX_txn *txn, int bad_bits) {
    if (unlikely(!txn))
      return MDBX_EINVAL;
  
    if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
      return MDBX_EBADSIGN;
  
    if (unlikely(txn->mt_flags & bad_bits))
      return MDBX_BAD_TXN;
  
    if (unlikely(F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)))
      return MDBX_EACCESS;
  
  #if MDBX_TXN_CHECKOWNER
    if (unlikely(txn->mt_owner != mdbx_thread_self()))
      return txn->mt_owner ? MDBX_THREAD_MISMATCH : MDBX_BAD_TXN;
  #endif /* MDBX_TXN_CHECKOWNER */
  
    return MDBX_SUCCESS;
  }
  
  int mdbx_txn_renew(MDBX_txn *txn) {
    if (unlikely(!txn))
      return MDBX_EINVAL;
  
    if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
      return MDBX_EBADSIGN;
  
    if (unlikely((txn->mt_flags & MDBX_TXN_RDONLY) == 0))
      return MDBX_EINVAL;
  
    int rc;
    if (unlikely(txn->mt_owner != 0 || !(txn->mt_flags & MDBX_TXN_FINISHED))) {
      rc = mdbx_txn_reset(txn);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  
    rc = mdbx_txn_renew0(txn, MDBX_TXN_RDONLY);
    if (rc == MDBX_SUCCESS) {
      txn->mt_owner = mdbx_thread_self();
      mdbx_debug("renew txn %" PRIaTXN "%c %p on env %p, root page %" PRIaPGNO
                 "/%" PRIaPGNO,
                 txn->mt_txnid, (txn->mt_flags & MDBX_TXN_RDONLY) ? 'r' : 'w',
                 (void *)txn, (void *)txn->mt_env, txn->mt_dbs[MAIN_DBI].md_root,
                 txn->mt_dbs[FREE_DBI].md_root);
    }
    return rc;
  }
  
  int mdbx_txn_begin(MDBX_env *env, MDBX_txn *parent, MDBX_txn_flags_t flags,
                     MDBX_txn **ret) {
    return __inline_mdbx_txn_begin(env, parent, flags, ret);
  }
  
  int mdbx_txn_set_userctx(MDBX_txn *txn, void *ctx) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED - MDBX_TXN_HAS_CHILD);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    txn->mt_userctx = ctx;
    return MDBX_SUCCESS;
  }
  
  void *mdbx_txn_get_userctx(const MDBX_txn *txn) {
    return check_txn(txn, MDBX_TXN_BLOCKED - MDBX_TXN_HAS_CHILD)
               ? nullptr
               : txn->mt_userctx;
  }
  
  int mdbx_txn_begin_ex(MDBX_env *env, MDBX_txn *parent, MDBX_txn_flags_t flags,
                        MDBX_txn **ret, void *context) {
    MDBX_txn *txn;
    unsigned size, tsize;
  
    if (unlikely(!ret))
      return MDBX_EINVAL;
    *ret = NULL;
  
    if (unlikely((flags & ~MDBX_TXN_RW_BEGIN_FLAGS) &&
                 (flags & ~MDBX_TXN_RO_BEGIN_FLAGS)))
      return MDBX_EINVAL;
  
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(env->me_flags & MDBX_RDONLY &
                 ~flags)) /* write txn in RDONLY env */
      return MDBX_EACCESS;
  
    if (unlikely(!env->me_map))
      return MDBX_EPERM;
  
    flags |= env->me_flags & MDBX_WRITEMAP;
  
    if (parent) {
      /* Nested transactions: Max 1 child, write txns only, no writemap */
      rc = check_txn_rw(parent,
                        MDBX_TXN_RDONLY | MDBX_WRITEMAP | MDBX_TXN_BLOCKED);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
  
      flags |= parent->mt_flags & (MDBX_TXN_RW_BEGIN_FLAGS | MDBX_TXN_SPILLS);
      /* Child txns save MDBX_pgstate and use own copy of cursors */
      size = env->me_maxdbs * (sizeof(MDBX_db) + sizeof(MDBX_cursor *) + 1);
      size += tsize = sizeof(MDBX_txn);
    } else if (flags & MDBX_TXN_RDONLY) {
      if (env->me_txn0 &&
          unlikely(env->me_txn0->mt_owner == mdbx_thread_self()) &&
          (mdbx_runtime_flags & MDBX_DBG_LEGACY_OVERLAP) == 0)
        return MDBX_TXN_OVERLAPPING;
      size = env->me_maxdbs * (sizeof(MDBX_db) + 1);
      size += tsize = sizeof(MDBX_txn);
    } else {
      /* Reuse preallocated write txn. However, do not touch it until
       * mdbx_txn_renew0() succeeds, since it currently may be active. */
      txn = env->me_txn0;
      goto renew;
    }
    if (unlikely((txn = mdbx_malloc(size)) == NULL)) {
      mdbx_debug("calloc: %s", "failed");
      return MDBX_ENOMEM;
    }
    memset(txn, 0, tsize);
    txn->mt_dbxs = env->me_dbxs; /* static */
    txn->mt_dbs = (MDBX_db *)((char *)txn + tsize);
    txn->mt_dbistate = (uint8_t *)txn + size - env->me_maxdbs;
    txn->mt_flags = flags;
    txn->mt_env = env;
  
    if (parent) {
      mdbx_tassert(txn, mdbx_dirtylist_check(parent));
      txn->tw.cursors = (MDBX_cursor **)(txn->mt_dbs + env->me_maxdbs);
      txn->mt_dbiseqs = parent->mt_dbiseqs;
      txn->tw.dirtylist = mdbx_malloc(sizeof(MDBX_DP) * (MDBX_DPL_TXNFULL + 1));
      txn->tw.reclaimed_pglist =
          mdbx_pnl_alloc(MDBX_PNL_ALLOCLEN(parent->tw.reclaimed_pglist));
      if (!txn->tw.dirtylist || !txn->tw.reclaimed_pglist) {
        mdbx_pnl_free(txn->tw.reclaimed_pglist);
        mdbx_free(txn->tw.dirtylist);
        mdbx_free(txn);
        return MDBX_ENOMEM;
      }
      mdbx_dpl_clear(txn->tw.dirtylist);
      memcpy(txn->tw.reclaimed_pglist, parent->tw.reclaimed_pglist,
             MDBX_PNL_SIZEOF(parent->tw.reclaimed_pglist));
      mdbx_assert(env, mdbx_pnl_check4assert(
                           txn->tw.reclaimed_pglist,
                           (txn->mt_next_pgno /* LY: intentional assignment here,
                                                     only for assertion */
                            = parent->mt_next_pgno)));
  
      txn->tw.last_reclaimed = parent->tw.last_reclaimed;
      if (parent->tw.lifo_reclaimed) {
        txn->tw.lifo_reclaimed = parent->tw.lifo_reclaimed;
        parent->tw.lifo_reclaimed =
            (void *)(intptr_t)MDBX_PNL_SIZE(parent->tw.lifo_reclaimed);
      }
  
      txn->tw.retired_pages = parent->tw.retired_pages;
      parent->tw.retired_pages =
          (void *)(intptr_t)MDBX_PNL_SIZE(parent->tw.retired_pages);
  
      txn->mt_txnid = parent->mt_txnid;
      txn->tw.dirtyroom = parent->tw.dirtyroom;
      txn->mt_geo = parent->mt_geo;
      txn->tw.loose_refund_wl = parent->tw.loose_refund_wl;
      txn->mt_canary = parent->mt_canary;
      parent->mt_flags |= MDBX_TXN_HAS_CHILD;
      parent->mt_child = txn;
      txn->mt_parent = parent;
      txn->mt_numdbs = parent->mt_numdbs;
      txn->mt_owner = parent->mt_owner;
      memcpy(txn->mt_dbs, parent->mt_dbs, txn->mt_numdbs * sizeof(MDBX_db));
      /* Copy parent's mt_dbistate, but clear DB_NEW */
      for (unsigned i = 0; i < txn->mt_numdbs; i++)
        txn->mt_dbistate[i] =
            parent->mt_dbistate[i] & ~(DBI_FRESH | DBI_CREAT | DBI_DIRTY);
      mdbx_tassert(parent,
                   parent->mt_parent ||
                       parent->tw.dirtyroom + parent->tw.dirtylist->length ==
                           MDBX_DPL_TXNFULL);
      env->me_txn = txn;
      rc = mdbx_cursor_shadow(parent, txn);
      if (unlikely(rc != MDBX_SUCCESS))
        mdbx_txn_end(txn, MDBX_END_FAIL_BEGINCHILD);
    } else { /* MDBX_TXN_RDONLY */
      txn->mt_dbiseqs = env->me_dbiseqs;
    renew:
      rc = mdbx_txn_renew0(txn, flags);
    }
  
    if (unlikely(rc != MDBX_SUCCESS)) {
      if (txn != env->me_txn0)
        mdbx_free(txn);
    } else {
      if (flags & (MDBX_TXN_RDONLY_PREPARE - MDBX_TXN_RDONLY))
        mdbx_assert(env, txn->mt_flags == (MDBX_TXN_RDONLY | MDBX_TXN_FINISHED));
      else if (flags & MDBX_TXN_RDONLY)
        mdbx_assert(env, (txn->mt_flags &
                          ~(MDBX_NOTLS | MDBX_TXN_RDONLY | MDBX_WRITEMAP |
                            /* Win32: SRWL flag */ MDBX_SHRINK_ALLOWED)) == 0);
      else
        mdbx_assert(env,
                    (txn->mt_flags & ~(MDBX_WRITEMAP | MDBX_SHRINK_ALLOWED |
                                       MDBX_NOMETASYNC | MDBX_SAFE_NOSYNC)) == 0);
      txn->mt_signature = MDBX_MT_SIGNATURE;
      txn->mt_userctx = context;
      *ret = txn;
      mdbx_debug("begin txn %" PRIaTXN "%c %p on env %p, root page %" PRIaPGNO
                 "/%" PRIaPGNO,
                 txn->mt_txnid, (flags & MDBX_TXN_RDONLY) ? 'r' : 'w',
                 (void *)txn, (void *)env, txn->mt_dbs[MAIN_DBI].md_root,
                 txn->mt_dbs[FREE_DBI].md_root);
    }
  
    return rc;
  }
  
  int mdbx_txn_info(const MDBX_txn *txn, MDBX_txn_info *info, bool scan_rlt) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED - MDBX_TXN_HAS_CHILD);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!info))
      return MDBX_EINVAL;
  
    MDBX_env *const env = txn->mt_env;
  #if MDBX_ENV_CHECKPID
    if (unlikely(env->me_pid != mdbx_getpid())) {
      env->me_flags |= MDBX_FATAL_ERROR;
      return MDBX_PANIC;
    }
  #endif /* MDBX_ENV_CHECKPID */
  
    info->txn_id = txn->mt_txnid;
    info->txn_space_used = pgno2bytes(env, txn->mt_geo.next);
  
    if (txn->mt_flags & MDBX_TXN_RDONLY) {
      const MDBX_meta *head_meta;
      txnid_t head_txnid;
      uint64_t head_retired;
      do {
        /* fetch info from volatile head */
        head_meta = mdbx_meta_head(env);
        head_txnid = mdbx_meta_txnid_fluid(env, head_meta);
        head_retired = head_meta->mm_pages_retired;
        info->txn_space_limit_soft = pgno2bytes(env, head_meta->mm_geo.now);
        info->txn_space_limit_hard = pgno2bytes(env, head_meta->mm_geo.upper);
        info->txn_space_leftover =
            pgno2bytes(env, head_meta->mm_geo.now - head_meta->mm_geo.next);
        mdbx_compiler_barrier();
      } while (unlikely(head_meta != mdbx_meta_head(env) ||
                        head_txnid != mdbx_meta_txnid_fluid(env, head_meta)));
  
      info->txn_reader_lag = head_txnid - info->txn_id;
      info->txn_space_dirty = info->txn_space_retired = 0;
      if (txn->to.reader &&
          head_retired > txn->to.reader->mr_snapshot_pages_retired) {
        info->txn_space_dirty = info->txn_space_retired =
            pgno2bytes(env, (pgno_t)(head_retired -
                                     txn->to.reader->mr_snapshot_pages_retired));
  
        size_t retired_next_reader = 0;
        MDBX_lockinfo *const lck = env->me_lck;
        if (scan_rlt && info->txn_reader_lag > 1 && lck) {
          /* find next more recent reader */
          txnid_t next_reader = head_txnid;
          const unsigned snap_nreaders = lck->mti_numreaders;
          for (unsigned i = 0; i < snap_nreaders; ++i) {
          retry:
            if (lck->mti_readers[i].mr_pid) {
              mdbx_jitter4testing(true);
              const txnid_t snap_txnid =
                  safe64_read(&lck->mti_readers[i].mr_txnid);
              const uint64_t snap_retired =
                  lck->mti_readers[i].mr_snapshot_pages_retired;
              mdbx_compiler_barrier();
              if (unlikely(snap_retired !=
                           lck->mti_readers[i].mr_snapshot_pages_retired) ||
                  snap_txnid != safe64_read(&lck->mti_readers[i].mr_txnid))
                goto retry;
              if (snap_txnid <= txn->mt_txnid) {
                retired_next_reader = 0;
                break;
              }
              if (snap_txnid < next_reader) {
                next_reader = snap_txnid;
                retired_next_reader = pgno2bytes(
                    env, (pgno_t)(snap_retired -
                                  txn->to.reader->mr_snapshot_pages_retired));
              }
            }
          }
        }
        info->txn_space_dirty = retired_next_reader;
      }
    } else {
      info->txn_space_limit_soft = pgno2bytes(env, txn->mt_geo.now);
      info->txn_space_limit_hard = pgno2bytes(env, txn->mt_geo.upper);
      info->txn_space_retired = pgno2bytes(
          env, txn->mt_child ? (unsigned)(uintptr_t)txn->tw.retired_pages
                             : MDBX_PNL_SIZE(txn->tw.retired_pages));
      info->txn_space_leftover = pgno2bytes(env, txn->tw.dirtyroom);
      info->txn_space_dirty =
          pgno2bytes(env, MDBX_DPL_TXNFULL - txn->tw.dirtyroom);
      info->txn_reader_lag = INT64_MAX;
      MDBX_lockinfo *const lck = env->me_lck;
      if (scan_rlt && lck) {
        txnid_t oldest_snapshot = txn->mt_txnid;
        const unsigned snap_nreaders = lck->mti_numreaders;
        if (snap_nreaders) {
          oldest_snapshot = mdbx_find_oldest(txn);
          if (oldest_snapshot == txn->mt_txnid - 1) {
            /* check if there is at least one reader */
            bool exists = false;
            for (unsigned i = 0; i < snap_nreaders; ++i) {
              if (lck->mti_readers[i].mr_pid &&
                  txn->mt_txnid > safe64_read(&lck->mti_readers[i].mr_txnid)) {
                exists = true;
                break;
              }
            }
            oldest_snapshot += !exists;
          }
        }
        info->txn_reader_lag = txn->mt_txnid - oldest_snapshot;
      }
    }
  
    return MDBX_SUCCESS;
  }
  
  MDBX_env *mdbx_txn_env(const MDBX_txn *txn) {
    if (unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE ||
                 txn->mt_env->me_signature != MDBX_ME_SIGNATURE))
      return NULL;
    return txn->mt_env;
  }
  
  uint64_t mdbx_txn_id(const MDBX_txn *txn) {
    if (unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE))
      return 0;
    return txn->mt_txnid;
  }
  
  int mdbx_txn_flags(const MDBX_txn *txn) {
    if (unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE))
      return -1;
    return txn->mt_flags;
  }
  
  /* Check for misused dbi handles */
  #define TXN_DBI_CHANGED(txn, dbi)                                              \
    ((txn)->mt_dbiseqs[dbi] != (txn)->mt_env->me_dbiseqs[dbi])
  
  static void dbi_import_locked(MDBX_txn *txn) {
    MDBX_env *const env = txn->mt_env;
    const unsigned n = env->me_numdbs;
    for (unsigned i = CORE_DBS; i < n; ++i) {
      if (i >= txn->mt_numdbs) {
        txn->mt_dbistate[i] = 0;
        if (!(txn->mt_flags & MDBX_TXN_RDONLY))
          txn->tw.cursors[i] = NULL;
      }
      if ((env->me_dbflags[i] & DB_VALID) &&
          !(txn->mt_dbistate[i] & DBI_USRVALID)) {
        txn->mt_dbiseqs[i] = env->me_dbiseqs[i];
        txn->mt_dbs[i].md_flags = env->me_dbflags[i] & DB_PERSISTENT_FLAGS;
        txn->mt_dbistate[i] = DBI_VALID | DBI_USRVALID | DBI_STALE;
        mdbx_tassert(txn, txn->mt_dbxs[i].md_cmp != NULL);
      }
    }
    txn->mt_numdbs = n;
  }
  
  /* Import DBI which opened after txn started into context */
  static __cold bool dbi_import(MDBX_txn *txn, MDBX_dbi dbi) {
    if (dbi < CORE_DBS || dbi >= txn->mt_env->me_numdbs)
      return false;
  
    mdbx_ensure(txn->mt_env, mdbx_fastmutex_acquire(&txn->mt_env->me_dbi_lock) ==
                                 MDBX_SUCCESS);
    dbi_import_locked(txn);
    mdbx_ensure(txn->mt_env, mdbx_fastmutex_release(&txn->mt_env->me_dbi_lock) ==
                                 MDBX_SUCCESS);
    return txn->mt_dbistate[dbi] & DBI_USRVALID;
  }
  
  /* Export or close DBI handles opened in this txn. */
  static void dbi_update(MDBX_txn *txn, int keep) {
    mdbx_tassert(txn, !txn->mt_parent && txn == txn->mt_env->me_txn0);
    MDBX_dbi n = txn->mt_numdbs;
    if (n) {
      bool locked = false;
      MDBX_env *const env = txn->mt_env;
  
      for (unsigned i = n; --i >= CORE_DBS;) {
        if (likely((txn->mt_dbistate[i] & DBI_CREAT) == 0))
          continue;
        if (!locked) {
          mdbx_ensure(env,
                      mdbx_fastmutex_acquire(&env->me_dbi_lock) == MDBX_SUCCESS);
          locked = true;
        }
        if (env->me_numdbs <= i || txn->mt_dbiseqs[i] != env->me_dbiseqs[i])
          continue /* dbi explicitly closed and/or then re-opened by other txn */;
        if (keep) {
          env->me_dbflags[i] = txn->mt_dbs[i].md_flags | DB_VALID;
        } else {
          char *ptr = env->me_dbxs[i].md_name.iov_base;
          if (ptr) {
            env->me_dbxs[i].md_name.iov_len = 0;
            mdbx_compiler_barrier();
            mdbx_assert(env, env->me_dbflags[i] == 0);
            env->me_dbiseqs[i]++;
            env->me_dbxs[i].md_name.iov_base = NULL;
            mdbx_free(ptr);
          }
        }
      }
  
      n = env->me_numdbs;
      if (n > CORE_DBS && unlikely(!(env->me_dbflags[n - 1] & DB_VALID))) {
        if (!locked) {
          mdbx_ensure(env,
                      mdbx_fastmutex_acquire(&env->me_dbi_lock) == MDBX_SUCCESS);
          locked = true;
        }
  
        n = env->me_numdbs;
        while (n > CORE_DBS && !(env->me_dbflags[n - 1] & DB_VALID))
          --n;
        env->me_numdbs = n;
      }
  
      if (unlikely(locked))
        mdbx_ensure(env,
                    mdbx_fastmutex_release(&env->me_dbi_lock) == MDBX_SUCCESS);
    }
  }
  
  /* End a transaction, except successful commit of a nested transaction.
   * May be called twice for readonly txns: First reset it, then abort.
   * [in] txn   the transaction handle to end
   * [in] mode  why and how to end the transaction */
  static int mdbx_txn_end(MDBX_txn *txn, unsigned mode) {
    MDBX_env *env = txn->mt_env;
    static const char *const names[] = MDBX_END_NAMES;
  
  #if MDBX_ENV_CHECKPID
    if (unlikely(txn->mt_env->me_pid != mdbx_getpid())) {
      env->me_flags |= MDBX_FATAL_ERROR;
      return MDBX_PANIC;
    }
  #endif /* MDBX_ENV_CHECKPID */
  
    mdbx_debug("%s txn %" PRIaTXN "%c %p on mdbenv %p, root page %" PRIaPGNO
               "/%" PRIaPGNO,
               names[mode & MDBX_END_OPMASK], txn->mt_txnid,
               (txn->mt_flags & MDBX_TXN_RDONLY) ? 'r' : 'w', (void *)txn,
               (void *)env, txn->mt_dbs[MAIN_DBI].md_root,
               txn->mt_dbs[FREE_DBI].md_root);
  
    mdbx_ensure(env, txn->mt_txnid >=
                         /* paranoia is appropriate here */ *env->me_oldest);
  
    int rc = MDBX_SUCCESS;
    if (F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)) {
      if (txn->to.reader) {
        MDBX_reader *slot = txn->to.reader;
        mdbx_assert(env, slot->mr_pid == env->me_pid);
        if (likely(!F_ISSET(txn->mt_flags, MDBX_TXN_FINISHED))) {
          mdbx_assert(env, txn->mt_txnid == slot->mr_txnid.inconsistent &&
                               slot->mr_txnid.inconsistent >=
                                   env->me_lck->mti_oldest_reader);
  #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
          mdbx_txn_valgrind(env, nullptr);
  #endif
          slot->mr_snapshot_pages_used = 0;
          safe64_reset(&slot->mr_txnid, false);
          env->me_lck->mti_readers_refresh_flag = true;
          mdbx_flush_incoherent_cpu_writeback();
        } else {
          mdbx_assert(env, slot->mr_pid == env->me_pid);
          mdbx_assert(env,
                      slot->mr_txnid.inconsistent >= SAFE64_INVALID_THRESHOLD);
        }
        if (mode & MDBX_END_SLOT) {
          if ((env->me_flags & MDBX_ENV_TXKEY) == 0)
            slot->mr_pid = 0;
          txn->to.reader = NULL;
        }
      }
  #if defined(_WIN32) || defined(_WIN64)
      if (txn->mt_flags & MDBX_SHRINK_ALLOWED)
        mdbx_srwlock_ReleaseShared(&env->me_remap_guard);
  #endif
      txn->mt_numdbs = 0; /* prevent further DBI activity */
      txn->mt_flags = MDBX_TXN_RDONLY | MDBX_TXN_FINISHED;
      txn->mt_owner = 0;
    } else if (!F_ISSET(txn->mt_flags, MDBX_TXN_FINISHED)) {
  #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
      if (txn == env->me_txn0)
        mdbx_txn_valgrind(env, nullptr);
  #endif
      if (!(mode & MDBX_END_EOTDONE)) /* !(already closed cursors) */
        mdbx_cursors_eot(txn, false);
      if (!(env->me_flags & MDBX_WRITEMAP))
        mdbx_dlist_free(txn);
  
      txn->mt_flags = MDBX_TXN_FINISHED;
      txn->mt_owner = 0;
      env->me_txn = txn->mt_parent;
      if (txn == env->me_txn0) {
        mdbx_assert(env, txn->mt_parent == NULL);
        /* Export or close DBI handles created in this txn */
        dbi_update(txn, mode & MDBX_END_UPDATE);
        mdbx_pnl_shrink(&txn->tw.retired_pages);
        mdbx_pnl_shrink(&txn->tw.reclaimed_pglist);
        /* The writer mutex was locked in mdbx_txn_begin. */
        mdbx_txn_unlock(env);
      } else {
        mdbx_assert(env, txn->mt_parent != NULL);
        MDBX_txn *const parent = txn->mt_parent;
        mdbx_assert(env, parent->mt_signature == MDBX_MT_SIGNATURE);
        mdbx_assert(env, parent->mt_child == txn &&
                             (parent->mt_flags & MDBX_TXN_HAS_CHILD) != 0);
        mdbx_assert(env, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist,
                                               txn->mt_next_pgno));
        mdbx_pnl_free(txn->tw.reclaimed_pglist);
        mdbx_pnl_free(txn->tw.spill_pages);
  
        if (txn->tw.lifo_reclaimed) {
          mdbx_assert(env, MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) >=
                               (unsigned)(uintptr_t)parent->tw.lifo_reclaimed);
          MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) =
              (unsigned)(uintptr_t)parent->tw.lifo_reclaimed;
          parent->tw.lifo_reclaimed = txn->tw.lifo_reclaimed;
        }
  
        if (txn->tw.retired_pages) {
          mdbx_assert(env, MDBX_PNL_SIZE(txn->tw.retired_pages) >=
                               (unsigned)(uintptr_t)parent->tw.retired_pages);
          MDBX_PNL_SIZE(txn->tw.retired_pages) =
              (unsigned)(uintptr_t)parent->tw.retired_pages;
          parent->tw.retired_pages = txn->tw.retired_pages;
        }
  
        mdbx_free(txn->tw.dirtylist);
        parent->mt_child = NULL;
        parent->mt_flags &= ~MDBX_TXN_HAS_CHILD;
  
        if (parent->mt_geo.upper != txn->mt_geo.upper ||
            parent->mt_geo.now != txn->mt_geo.now) {
          /* undo resize performed by child txn */
          rc = mdbx_mapresize_implicit(env, parent->mt_next_pgno,
                                       parent->mt_geo.now, parent->mt_geo.upper);
          if (rc == MDBX_RESULT_TRUE) {
            /* unable undo resize (it is regular for Windows),
             * therefore promote size changes from child to the parent txn */
            mdbx_warning("unable undo resize performed by child txn, promote to "
                         "the parent (%u->%u, %u->%u)",
                         txn->mt_geo.now, parent->mt_geo.now, txn->mt_geo.upper,
                         parent->mt_geo.upper);
            parent->mt_geo.now = txn->mt_geo.now;
            parent->mt_geo.upper = txn->mt_geo.upper;
            rc = MDBX_SUCCESS;
          } else if (unlikely(rc != MDBX_SUCCESS)) {
            mdbx_error("error %d while undo resize performed by child txn, fail "
                       "the parent",
                       rc);
            parent->mt_flags |= MDBX_TXN_ERROR;
            if (!env->me_dxb_mmap.address)
              env->me_flags |= MDBX_FATAL_ERROR;
          }
        }
      }
    }
  
    mdbx_assert(env, txn == env->me_txn0 || txn->mt_owner == 0);
    if ((mode & MDBX_END_FREE) != 0 && txn != env->me_txn0) {
      txn->mt_signature = 0;
      mdbx_free(txn);
    }
  
    return rc;
  }
  
  int mdbx_txn_reset(MDBX_txn *txn) {
    int rc = check_txn(txn, 0);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    /* This call is only valid for read-only txns */
    if (unlikely((txn->mt_flags & MDBX_TXN_RDONLY) == 0))
      return MDBX_EINVAL;
  
    /* LY: don't close DBI-handles */
    rc = mdbx_txn_end(txn, MDBX_END_RESET | MDBX_END_UPDATE);
    if (rc == MDBX_SUCCESS) {
      mdbx_tassert(txn, txn->mt_signature == MDBX_MT_SIGNATURE);
      mdbx_tassert(txn, txn->mt_owner == 0);
    }
    return rc;
  }
  
  int mdbx_txn_break(MDBX_txn *txn) {
    do {
      int rc = check_txn(txn, 0);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      txn->mt_flags |= MDBX_TXN_ERROR;
      if (txn->mt_flags & MDBX_TXN_RDONLY)
        break;
      txn = txn->mt_child;
    } while (txn);
    return MDBX_SUCCESS;
  }
  
  int mdbx_txn_abort(MDBX_txn *txn) {
    int rc = check_txn(txn, 0);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY))
      /* LY: don't close DBI-handles */
      return mdbx_txn_end(txn, MDBX_END_ABORT | MDBX_END_UPDATE | MDBX_END_SLOT |
                                   MDBX_END_FREE);
  
    if (txn->mt_child)
      mdbx_txn_abort(txn->mt_child);
  
    return mdbx_txn_end(txn, MDBX_END_ABORT | MDBX_END_SLOT | MDBX_END_FREE);
  }
  
  /* Count all the pages in each DB and in the freelist and make sure
   * it matches the actual number of pages being used.
   * All named DBs must be open for a correct count. */
  static __cold int mdbx_audit_ex(MDBX_txn *txn, unsigned retired_stored,
                                  bool dont_filter_gc) {
    pgno_t pending = 0;
    if ((txn->mt_flags & MDBX_TXN_RDONLY) == 0) {
      pending = txn->tw.loose_count + MDBX_PNL_SIZE(txn->tw.reclaimed_pglist) +
                (MDBX_PNL_SIZE(txn->tw.retired_pages) - retired_stored) +
                txn->tw.retired2parent_count;
      for (MDBX_txn *parent = txn->mt_parent; parent; parent = parent->mt_parent)
        pending += parent->tw.loose_count;
    }
  
    MDBX_cursor_couple cx;
    int rc = mdbx_cursor_init(&cx.outer, txn, FREE_DBI);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    pgno_t freecount = 0;
    MDBX_val key, data;
    while ((rc = mdbx_cursor_get(&cx.outer, &key, &data, MDBX_NEXT)) == 0) {
      if (!dont_filter_gc) {
        if (unlikely(key.iov_len != sizeof(txnid_t)))
          return MDBX_CORRUPTED;
        txnid_t id = unaligned_peek_u64(4, key.iov_base);
        if (txn->tw.lifo_reclaimed) {
          for (unsigned i = 1; i <= MDBX_PNL_SIZE(txn->tw.lifo_reclaimed); ++i)
            if (id == txn->tw.lifo_reclaimed[i])
              goto skip;
        } else if (id <= txn->tw.last_reclaimed)
          goto skip;
      }
  
      freecount += *(pgno_t *)data.iov_base;
    skip:;
    }
    mdbx_tassert(txn, rc == MDBX_NOTFOUND);
  
    for (MDBX_dbi i = FREE_DBI; i < txn->mt_numdbs; i++)
      txn->mt_dbistate[i] &= ~DBI_AUDITED;
  
    pgno_t count = 0;
    for (MDBX_dbi i = FREE_DBI; i <= MAIN_DBI; i++) {
      if (!(txn->mt_dbistate[i] & DBI_VALID))
        continue;
      rc = mdbx_cursor_init(&cx.outer, txn, i);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      txn->mt_dbistate[i] |= DBI_AUDITED;
      if (txn->mt_dbs[i].md_root == P_INVALID)
        continue;
      count += txn->mt_dbs[i].md_branch_pages + txn->mt_dbs[i].md_leaf_pages +
               txn->mt_dbs[i].md_overflow_pages;
  
      if (i != MAIN_DBI)
        continue;
      rc = mdbx_page_search(&cx.outer, NULL, MDBX_PS_FIRST);
      while (rc == MDBX_SUCCESS) {
        MDBX_page *mp = cx.outer.mc_pg[cx.outer.mc_top];
        for (unsigned j = 0; j < page_numkeys(mp); j++) {
          MDBX_node *node = page_node(mp, j);
          if (node_flags(node) == F_SUBDATA) {
            if (unlikely(node_ds(node) != sizeof(MDBX_db)))
              return MDBX_CORRUPTED;
            MDBX_db db_copy, *db;
            memcpy(db = &db_copy, node_data(node), sizeof(db_copy));
            if ((txn->mt_flags & MDBX_TXN_RDONLY) == 0) {
              for (MDBX_dbi k = txn->mt_numdbs; --k > MAIN_DBI;) {
                if ((txn->mt_dbistate[k] & DBI_VALID) &&
                    /* txn->mt_dbxs[k].md_name.iov_len > 0 && */
                    node_ks(node) == txn->mt_dbxs[k].md_name.iov_len &&
                    memcmp(node_key(node), txn->mt_dbxs[k].md_name.iov_base,
                           node_ks(node)) == 0) {
                  txn->mt_dbistate[k] |= DBI_AUDITED;
                  if (txn->mt_dbistate[k] & DBI_DIRTY) {
                    mdbx_tassert(txn, (txn->mt_dbistate[k] & DBI_STALE) == 0);
                    db = txn->mt_dbs + k;
                  }
                  break;
                }
              }
            }
            count +=
                db->md_branch_pages + db->md_leaf_pages + db->md_overflow_pages;
          }
        }
        rc = mdbx_cursor_sibling(&cx.outer, SIBLING_RIGHT);
      }
      mdbx_tassert(txn, rc == MDBX_NOTFOUND);
    }
  
    for (MDBX_dbi i = FREE_DBI; i < txn->mt_numdbs; i++) {
      if ((txn->mt_dbistate[i] & (DBI_VALID | DBI_AUDITED | DBI_STALE)) !=
          DBI_VALID)
        continue;
      if (F_ISSET(txn->mt_dbistate[i], DBI_DIRTY | DBI_CREAT)) {
        count += txn->mt_dbs[i].md_branch_pages + txn->mt_dbs[i].md_leaf_pages +
                 txn->mt_dbs[i].md_overflow_pages;
      } else {
        mdbx_warning("audit %s@%" PRIaTXN
                     ": unable account dbi %d / \"%*s\", state 0x%02x",
                     txn->mt_parent ? "nested-" : "", txn->mt_txnid, i,
                     (int)txn->mt_dbxs[i].md_name.iov_len,
                     (const char *)txn->mt_dbxs[i].md_name.iov_base,
                     txn->mt_dbistate[i]);
      }
    }
  
    if (pending + freecount + count + NUM_METAS == txn->mt_next_pgno)
      return MDBX_SUCCESS;
  
    if ((txn->mt_flags & MDBX_TXN_RDONLY) == 0)
      mdbx_error("audit @%" PRIaTXN ": %u(pending) = %u(loose-count) + "
                 "%u(reclaimed-list) + %u(retired-pending) - %u(retired-stored) "
                 "+ %u(retired2parent)",
                 txn->mt_txnid, pending, txn->tw.loose_count,
                 MDBX_PNL_SIZE(txn->tw.reclaimed_pglist),
                 txn->tw.retired_pages ? MDBX_PNL_SIZE(txn->tw.retired_pages) : 0,
                 retired_stored, txn->tw.retired2parent_count);
    mdbx_error("audit @%" PRIaTXN ": %" PRIaPGNO "(pending) + %" PRIaPGNO
               "(free) + %" PRIaPGNO "(count) = %" PRIaPGNO
               "(total) <> %" PRIaPGNO "(next-pgno)",
               txn->mt_txnid, pending, freecount, count + NUM_METAS,
               pending + freecount + count + NUM_METAS, txn->mt_next_pgno);
    return MDBX_PROBLEM;
  }
  
  static __always_inline unsigned backlog_size(MDBX_txn *txn) {
    return MDBX_PNL_SIZE(txn->tw.reclaimed_pglist) + txn->tw.loose_count;
  }
  
  /* LY: Prepare a backlog of pages to modify GC itself,
   * while reclaiming is prohibited. It should be enough to prevent search
   * in mdbx_page_alloc() during a deleting, when GC tree is unbalanced. */
  static int mdbx_prep_backlog(MDBX_txn *txn, MDBX_cursor *gc_cursor,
                               const size_t pnl_bytes) {
    const unsigned linear4list = number_of_ovpages(txn->mt_env, pnl_bytes);
    const unsigned backlog4cow = txn->mt_dbs[FREE_DBI].md_depth;
    const unsigned backlog4rebalance = backlog4cow + 1;
  
    if (likely(linear4list == 1 &&
               backlog_size(txn) > (pnl_bytes
                                        ? backlog4rebalance
                                        : (backlog4cow + backlog4rebalance))))
      return MDBX_SUCCESS;
  
    mdbx_trace(">> pnl_bytes %zu, backlog %u, 4list %u, 4cow %u, 4rebalance %u",
               pnl_bytes, backlog_size(txn), linear4list, backlog4cow,
               backlog4rebalance);
  
    gc_cursor->mc_flags &= ~C_RECLAIMING;
    int err = mdbx_cursor_touch(gc_cursor);
    mdbx_trace("== after-touch, backlog %u, err %d", backlog_size(txn), err);
  
    if (linear4list > 1 && err == MDBX_SUCCESS) {
      err = mdbx_page_alloc(gc_cursor, linear4list, nullptr,
                            MDBX_ALLOC_GC | MDBX_ALLOC_CACHE);
      mdbx_trace("== after-4linear, backlog %u, err %d", backlog_size(txn), err);
    }
  
    while (backlog_size(txn) < backlog4cow + linear4list && err == MDBX_SUCCESS)
      err = mdbx_page_alloc(gc_cursor, 1, NULL, MDBX_ALLOC_GC);
  
    gc_cursor->mc_flags |= C_RECLAIMING;
    mdbx_trace("<< backlog %u, err %d", backlog_size(txn), err);
    return (err != MDBX_NOTFOUND) ? err : MDBX_SUCCESS;
  }
  
  static __inline void clean_reserved_gc_pnl(MDBX_env *env, MDBX_val pnl) {
    /* PNL is initially empty, zero out at least the length */
    memset(pnl.iov_base, 0, sizeof(pgno_t));
    if ((env->me_flags & (MDBX_WRITEMAP | MDBX_NOMEMINIT)) == 0)
      /* zero out to avoid leaking values from uninitialized malloc'ed memory
       * to the file in non-writemap mode if length of the saving page-list
       * was changed during space reservation. */
      memset(pnl.iov_base, 0, pnl.iov_len);
  }
  
  /* Cleanup reclaimed GC records, than save the retired-list as of this
   * transaction to GC (aka freeDB). This recursive changes the reclaimed-list
   * loose-list and retired-list. Keep trying until it stabilizes. */
  static int mdbx_update_gc(MDBX_txn *txn) {
    /* txn->tw.reclaimed_pglist[] can grow and shrink during this call.
     * txn->tw.last_reclaimed and txn->tw.retired_pages[] can only grow.
     * Page numbers cannot disappear from txn->tw.retired_pages[]. */
    MDBX_env *const env = txn->mt_env;
    const bool lifo = (env->me_flags & MDBX_LIFORECLAIM) != 0;
    const char *dbg_prefix_mode = lifo ? "    lifo" : "    fifo";
    (void)dbg_prefix_mode;
    mdbx_trace("\n>>> @%" PRIaTXN, txn->mt_txnid);
  
    unsigned retired_stored = 0, loop = 0;
    MDBX_cursor_couple couple;
    int rc = mdbx_cursor_init(&couple.outer, txn, FREE_DBI);
    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout_notracking;
  
    couple.outer.mc_flags |= C_RECLAIMING;
    couple.outer.mc_next = txn->tw.cursors[FREE_DBI];
    txn->tw.cursors[FREE_DBI] = &couple.outer;
  
  retry:
    ++loop;
  retry_noaccount:
    mdbx_trace("%s", " >> restart");
    mdbx_tassert(
        txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist, txn->mt_next_pgno));
    mdbx_tassert(txn, mdbx_dirtylist_check(txn));
    mdbx_tassert(txn, txn->tw.dirtyroom + txn->tw.dirtylist->length ==
                          MDBX_DPL_TXNFULL);
    if (unlikely(/* paranoia */ loop > ((MDBX_DEBUG > 0) ? 9 : 99))) {
      mdbx_error("too more loops %u, bailout", loop);
      rc = MDBX_PROBLEM;
      goto bailout;
    }
  
    rc = mdbx_prep_backlog(txn, &couple.outer,
                           MDBX_PNL_SIZEOF(txn->tw.retired_pages));
    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout;
  
    unsigned settled = 0, cleaned_gc_slot = 0, reused_gc_slot = 0,
             filled_gc_slot = ~0u;
    txnid_t cleaned_gc_id = 0, gc_rid = txn->tw.last_reclaimed;
    while (true) {
      /* Come back here after each Put() in case retired-list changed */
      MDBX_val key, data;
      mdbx_trace("%s", " >> continue");
  
      mdbx_tassert(txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist,
                                              txn->mt_next_pgno));
      if (lifo) {
        if (cleaned_gc_slot < (txn->tw.lifo_reclaimed
                                   ? MDBX_PNL_SIZE(txn->tw.lifo_reclaimed)
                                   : 0)) {
          settled = 0;
          cleaned_gc_slot = 0;
          reused_gc_slot = 0;
          filled_gc_slot = ~0u;
          /* LY: cleanup reclaimed records. */
          do {
            cleaned_gc_id = txn->tw.lifo_reclaimed[++cleaned_gc_slot];
            mdbx_tassert(txn,
                         cleaned_gc_slot > 0 && cleaned_gc_id < *env->me_oldest);
            key.iov_base = &cleaned_gc_id;
            key.iov_len = sizeof(cleaned_gc_id);
            rc = mdbx_cursor_get(&couple.outer, &key, NULL, MDBX_SET);
            if (rc == MDBX_NOTFOUND)
              continue;
            if (unlikely(rc != MDBX_SUCCESS))
              goto bailout;
            rc = mdbx_prep_backlog(txn, &couple.outer, 0);
            if (unlikely(rc != MDBX_SUCCESS))
              goto bailout;
            mdbx_tassert(txn, cleaned_gc_id < *env->me_oldest);
            mdbx_trace("%s.cleanup-reclaimed-id [%u]%" PRIaTXN, dbg_prefix_mode,
                       cleaned_gc_slot, cleaned_gc_id);
            rc = mdbx_cursor_del(&couple.outer, 0);
            if (unlikely(rc != MDBX_SUCCESS))
              goto bailout;
          } while (cleaned_gc_slot < MDBX_PNL_SIZE(txn->tw.lifo_reclaimed));
          mdbx_txl_sort(txn->tw.lifo_reclaimed);
        }
      } else {
        /* If using records from GC which we have not yet deleted,
         * now delete them and any we reserved for tw.reclaimed_pglist. */
        while (cleaned_gc_id <= txn->tw.last_reclaimed) {
          gc_rid = cleaned_gc_id;
          settled = 0;
          rc = mdbx_cursor_first(&couple.outer, &key, NULL);
          if (unlikely(rc != MDBX_SUCCESS)) {
            if (rc == MDBX_NOTFOUND)
              break;
            goto bailout;
          }
          if (unlikely(key.iov_len != sizeof(txnid_t))) {
            rc = MDBX_CORRUPTED;
            goto bailout;
          }
          cleaned_gc_id = unaligned_peek_u64(4, key.iov_base);
          if (unlikely(cleaned_gc_id < MIN_TXNID || cleaned_gc_id > MAX_TXNID)) {
            rc = MDBX_CORRUPTED;
            goto bailout;
          }
          if (cleaned_gc_id > txn->tw.last_reclaimed)
            break;
          if (cleaned_gc_id < txn->tw.last_reclaimed) {
            rc = mdbx_prep_backlog(txn, &couple.outer, 0);
            if (unlikely(rc != MDBX_SUCCESS))
              goto bailout;
          }
          mdbx_tassert(txn, cleaned_gc_id <= txn->tw.last_reclaimed);
          mdbx_tassert(txn, cleaned_gc_id < *env->me_oldest);
          mdbx_trace("%s.cleanup-reclaimed-id %" PRIaTXN, dbg_prefix_mode,
                     cleaned_gc_id);
          rc = mdbx_cursor_del(&couple.outer, 0);
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
        }
      }
  
      mdbx_tassert(txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist,
                                              txn->mt_next_pgno));
      mdbx_tassert(txn, mdbx_dirtylist_check(txn));
      mdbx_tassert(txn, txn->tw.dirtyroom + txn->tw.dirtylist->length ==
                            MDBX_DPL_TXNFULL);
      if (mdbx_audit_enabled()) {
        rc = mdbx_audit_ex(txn, retired_stored, false);
        if (unlikely(rc != MDBX_SUCCESS))
          goto bailout;
      }
  
      /* return suitable into unallocated space */
      if (mdbx_refund(txn)) {
        mdbx_tassert(txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist,
                                                txn->mt_next_pgno));
        if (mdbx_audit_enabled()) {
          rc = mdbx_audit_ex(txn, retired_stored, false);
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
        }
      }
  
      /* handle loose pages - put ones into the reclaimed- or retired-list */
      if (txn->tw.loose_pages) {
        /* Return loose page numbers to tw.reclaimed_pglist,
         * though usually none are left at this point.
         * The pages themselves remain in dirtylist. */
        if (unlikely(!txn->tw.lifo_reclaimed && txn->tw.last_reclaimed < 1)) {
          if (txn->tw.loose_count > 0) {
            /* Put loose page numbers in tw.retired_pages,
             * since unable to return them to tw.reclaimed_pglist. */
            if (unlikely((rc = mdbx_pnl_need(&txn->tw.retired_pages,
                                             txn->tw.loose_count)) != 0))
              goto bailout;
            for (MDBX_page *mp = txn->tw.loose_pages; mp; mp = mp->mp_next)
              mdbx_pnl_xappend(txn->tw.retired_pages, mp->mp_pgno);
            mdbx_trace("%s: append %u loose-pages to retired-pages",
                       dbg_prefix_mode, txn->tw.loose_count);
          }
        } else {
          /* Room for loose pages + temp PNL with same */
          rc = mdbx_pnl_need(&txn->tw.reclaimed_pglist,
                             2 * txn->tw.loose_count + 2);
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
          MDBX_PNL loose = txn->tw.reclaimed_pglist +
                           MDBX_PNL_ALLOCLEN(txn->tw.reclaimed_pglist) -
                           txn->tw.loose_count - 1;
          unsigned count = 0;
          for (MDBX_page *mp = txn->tw.loose_pages; mp; mp = mp->mp_next) {
            mdbx_tassert(txn, mp->mp_flags == (P_LOOSE | P_DIRTY));
            loose[++count] = mp->mp_pgno;
          }
          mdbx_tassert(txn, count == txn->tw.loose_count);
          MDBX_PNL_SIZE(loose) = count;
          mdbx_pnl_sort(loose);
          mdbx_pnl_xmerge(txn->tw.reclaimed_pglist, loose);
          mdbx_trace("%s: append %u loose-pages to reclaimed-pages",
                     dbg_prefix_mode, txn->tw.loose_count);
        }
  
        /* filter-out list of dirty-pages from loose-pages */
        const MDBX_DPL dl = txn->tw.dirtylist;
        unsigned w = 0;
        for (unsigned r = w; ++r <= dl->length;) {
          MDBX_page *dp = dl[r].ptr;
          mdbx_tassert(txn, (dp->mp_flags & P_DIRTY));
          mdbx_tassert(txn, dl[r].pgno + (IS_OVERFLOW(dp) ? dp->mp_pages : 1) <=
                                txn->mt_next_pgno);
          if ((dp->mp_flags & P_LOOSE) == 0) {
            if (++w != r)
              dl[w] = dl[r];
          } else {
            mdbx_tassert(txn, dp->mp_flags == (P_LOOSE | P_DIRTY));
            if ((env->me_flags & MDBX_WRITEMAP) == 0)
              mdbx_dpage_free(env, dp, 1);
          }
        }
        mdbx_trace("%s: filtered-out loose-pages from %u -> %u dirty-pages",
                   dbg_prefix_mode, dl->length, w);
        mdbx_tassert(txn, txn->tw.loose_count == dl->length - w);
        dl->length = w;
        dl->sorted = 0;
        txn->tw.dirtyroom += txn->tw.loose_count;
        txn->tw.loose_pages = NULL;
        txn->tw.loose_count = 0;
      }
  
      const unsigned amount = (unsigned)MDBX_PNL_SIZE(txn->tw.reclaimed_pglist);
      /* handle retired-list - store ones into single gc-record */
      if (retired_stored < MDBX_PNL_SIZE(txn->tw.retired_pages)) {
        if (unlikely(!retired_stored)) {
          /* Make sure last page of GC is touched and on retired-list */
          couple.outer.mc_flags &= ~C_RECLAIMING;
          rc = mdbx_page_search(&couple.outer, NULL,
                                MDBX_PS_LAST | MDBX_PS_MODIFY);
          couple.outer.mc_flags |= C_RECLAIMING;
          if (unlikely(rc != MDBX_SUCCESS) && rc != MDBX_NOTFOUND)
            goto bailout;
        }
        /* Write to last page of GC */
        key.iov_len = sizeof(txn->mt_txnid);
        key.iov_base = &txn->mt_txnid;
        do {
          data.iov_len = MDBX_PNL_SIZEOF(txn->tw.retired_pages);
          mdbx_prep_backlog(txn, &couple.outer, data.iov_len);
          rc = mdbx_cursor_put(&couple.outer, &key, &data, MDBX_RESERVE);
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
          /* Retry if tw.retired_pages[] grew during the Put() */
        } while (data.iov_len < MDBX_PNL_SIZEOF(txn->tw.retired_pages));
  
        retired_stored = (unsigned)MDBX_PNL_SIZE(txn->tw.retired_pages);
        mdbx_pnl_sort(txn->tw.retired_pages);
        mdbx_assert(env, data.iov_len == MDBX_PNL_SIZEOF(txn->tw.retired_pages));
        memcpy(data.iov_base, txn->tw.retired_pages, data.iov_len);
  
        mdbx_trace("%s.put-retired #%u @ %" PRIaTXN, dbg_prefix_mode,
                   retired_stored, txn->mt_txnid);
  
        if (mdbx_log_enabled(MDBX_LOG_EXTRA)) {
          unsigned i = retired_stored;
          mdbx_debug_extra("PNL write txn %" PRIaTXN " root %" PRIaPGNO
                           " num %u, PNL",
                           txn->mt_txnid, txn->mt_dbs[FREE_DBI].md_root, i);
          for (; i; i--)
            mdbx_debug_extra_print(" %" PRIaPGNO, txn->tw.retired_pages[i]);
          mdbx_debug_extra_print("%s", "\n");
        }
        if (unlikely(amount != MDBX_PNL_SIZE(txn->tw.reclaimed_pglist))) {
          mdbx_trace("%s.reclaimed-list changed %u -> %u, retry", dbg_prefix_mode,
                     amount, (unsigned)MDBX_PNL_SIZE(txn->tw.reclaimed_pglist));
          goto retry_noaccount /* rare case, but avoids GC fragmentation and one
                                  cycle. */
              ;
        }
        continue;
      }
  
      /* handle reclaimed and lost pages - merge and store both into gc */
      mdbx_tassert(txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist,
                                              txn->mt_next_pgno));
      mdbx_tassert(txn, txn->tw.loose_count == 0);
  
      mdbx_trace("%s", " >> reserving");
      if (mdbx_audit_enabled()) {
        rc = mdbx_audit_ex(txn, retired_stored, false);
        if (unlikely(rc != MDBX_SUCCESS))
          goto bailout;
      }
      const unsigned left = amount - settled;
      mdbx_trace("%s: amount %u, settled %d, left %d, lifo-reclaimed-slots %u, "
                 "reused-gc-slots %u",
                 dbg_prefix_mode, amount, settled, (int)left,
                 txn->tw.lifo_reclaimed
                     ? (unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed)
                     : 0,
                 reused_gc_slot);
      if (0 >= (int)left)
        break;
  
      const unsigned prefer_max_scatter = 257;
      txnid_t reservation_gc_id;
      if (lifo) {
        if (txn->tw.lifo_reclaimed == nullptr) {
          txn->tw.lifo_reclaimed = mdbx_txl_alloc();
          if (unlikely(!txn->tw.lifo_reclaimed)) {
            rc = MDBX_ENOMEM;
            goto bailout;
          }
        }
        if ((unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) <
                prefer_max_scatter &&
            left > ((unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) -
                    reused_gc_slot) *
                       env->me_maxgc_ov1page) {
  
          /* LY: need just a txn-id for save page list. */
          bool need_cleanup = false;
          txnid_t snap_oldest;
        retry_rid:
          couple.outer.mc_flags &= ~C_RECLAIMING;
          do {
            snap_oldest = mdbx_find_oldest(txn);
            rc = mdbx_page_alloc(&couple.outer, 0, NULL, MDBX_ALLOC_GC);
            if (likely(rc == MDBX_SUCCESS)) {
              mdbx_trace("%s: took @%" PRIaTXN " from GC", dbg_prefix_mode,
                         MDBX_PNL_LAST(txn->tw.lifo_reclaimed));
              need_cleanup = true;
            }
          } while (rc == MDBX_SUCCESS &&
                   (unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) <
                       prefer_max_scatter &&
                   left > ((unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) -
                           reused_gc_slot) *
                              env->me_maxgc_ov1page);
          couple.outer.mc_flags |= C_RECLAIMING;
  
          if (likely(rc == MDBX_SUCCESS)) {
            mdbx_trace("%s: got enough from GC.", dbg_prefix_mode);
            continue;
          } else if (unlikely(rc != MDBX_NOTFOUND))
            /* LY: some troubles... */
            goto bailout;
  
          if (MDBX_PNL_SIZE(txn->tw.lifo_reclaimed)) {
            if (need_cleanup)
              mdbx_txl_sort(txn->tw.lifo_reclaimed);
            gc_rid = MDBX_PNL_LAST(txn->tw.lifo_reclaimed);
          } else {
            mdbx_tassert(txn, txn->tw.last_reclaimed == 0);
            if (unlikely(mdbx_find_oldest(txn) != snap_oldest))
              /* should retry mdbx_page_alloc(MDBX_ALLOC_GC)
               * if the oldest reader changes since the last attempt */
              goto retry_rid;
            /* no reclaimable GC entries,
             * therefore no entries with ID < mdbx_find_oldest(txn) */
            txn->tw.last_reclaimed = gc_rid = snap_oldest - 1;
            mdbx_trace("%s: none recycled yet, set rid to @%" PRIaTXN,
                       dbg_prefix_mode, gc_rid);
          }
  
          /* LY: GC is empty, will look any free txn-id in high2low order. */
          while (MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) < prefer_max_scatter &&
                 left > ((unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) -
                         reused_gc_slot) *
                            env->me_maxgc_ov1page) {
            if (unlikely(gc_rid < 2)) {
              if (unlikely(MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) <=
                           reused_gc_slot)) {
                mdbx_notice("** restart: reserve depleted (reused_gc_slot %u >= "
                            "lifo_reclaimed %u" PRIaTXN,
                            reused_gc_slot,
                            (unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed));
                goto retry;
              }
              break;
            }
  
            mdbx_tassert(txn, gc_rid >= MIN_TXNID && gc_rid <= MAX_TXNID);
            rc = mdbx_txl_append(&txn->tw.lifo_reclaimed, --gc_rid);
            if (unlikely(rc != MDBX_SUCCESS))
              goto bailout;
  
            if (reused_gc_slot)
              /* rare case, but it is better to clear and re-create GC entries
               * with less fragmentation. */
              need_cleanup = true;
            else
              cleaned_gc_slot +=
                  1 /* mark cleanup is not needed for added slot. */;
  
            mdbx_trace("%s: append @%" PRIaTXN
                       " to lifo-reclaimed, cleaned-gc-slot = %u",
                       dbg_prefix_mode, gc_rid, cleaned_gc_slot);
          }
  
          if (need_cleanup) {
            cleaned_gc_slot = 0;
            mdbx_trace("%s: restart inner-loop to clear and re-create GC entries",
                       dbg_prefix_mode);
            continue;
          }
        }
  
        const unsigned i =
            (unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) - reused_gc_slot;
        mdbx_tassert(txn, i > 0 && i <= MDBX_PNL_SIZE(txn->tw.lifo_reclaimed));
        reservation_gc_id = txn->tw.lifo_reclaimed[i];
        mdbx_trace("%s: take @%" PRIaTXN " from lifo-reclaimed[%u]",
                   dbg_prefix_mode, reservation_gc_id, i);
      } else {
        mdbx_tassert(txn, txn->tw.lifo_reclaimed == NULL);
        if (unlikely(gc_rid == 0)) {
          gc_rid = mdbx_find_oldest(txn) - 1;
          rc = mdbx_cursor_get(&couple.outer, &key, NULL, MDBX_FIRST);
          if (rc == MDBX_SUCCESS) {
            if (unlikely(key.iov_len != sizeof(txnid_t))) {
              rc = MDBX_CORRUPTED;
              goto bailout;
            }
            txnid_t gc_first = unaligned_peek_u64(4, key.iov_base);
            if (unlikely(gc_first < MIN_TXNID || gc_first > MAX_TXNID)) {
              rc = MDBX_CORRUPTED;
              goto bailout;
            }
            if (gc_rid >= gc_first)
              gc_rid = gc_first - 1;
            if (unlikely(gc_rid == 0)) {
              mdbx_error("%s", "** no GC tail-space to store");
              goto retry;
            }
          } else if (rc != MDBX_NOTFOUND)
            goto bailout;
          txn->tw.last_reclaimed = gc_rid;
        }
        reservation_gc_id = gc_rid--;
        mdbx_trace("%s: take @%" PRIaTXN " from head-gc-id", dbg_prefix_mode,
                   reservation_gc_id);
      }
      ++reused_gc_slot;
  
      unsigned chunk = left;
      if (unlikely(chunk > env->me_maxgc_ov1page)) {
        const unsigned avail_gc_slots =
            txn->tw.lifo_reclaimed
                ? (unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) -
                      reused_gc_slot + 1
                : (gc_rid < INT16_MAX) ? (unsigned)gc_rid : INT16_MAX;
        if (avail_gc_slots > 1) {
          if (chunk < env->me_maxgc_ov1page * 2)
            chunk /= 2;
          else {
            const unsigned threshold =
                env->me_maxgc_ov1page * ((avail_gc_slots < prefer_max_scatter)
                                             ? avail_gc_slots
                                             : prefer_max_scatter);
            if (left < threshold)
              chunk = env->me_maxgc_ov1page;
            else {
              const unsigned tail = left - threshold + env->me_maxgc_ov1page + 1;
              unsigned span = 1;
              unsigned avail = (unsigned)((pgno2bytes(env, span) - PAGEHDRSZ) /
                                          sizeof(pgno_t)) /*- 1 + span */;
              if (tail > avail) {
                for (unsigned i = amount - span; i > 0; --i) {
                  if (MDBX_PNL_ASCENDING
                          ? (txn->tw.reclaimed_pglist[i] + span)
                          : (txn->tw.reclaimed_pglist[i] - span) ==
                                txn->tw.reclaimed_pglist[i + span]) {
                    span += 1;
                    avail = (unsigned)((pgno2bytes(env, span) - PAGEHDRSZ) /
                                       sizeof(pgno_t)) -
                            1 + span;
                    if (avail >= tail)
                      break;
                  }
                }
              }
  
              chunk = (avail >= tail) ? tail - span
                                      : (avail_gc_slots > 3 &&
                                         reused_gc_slot < prefer_max_scatter - 3)
                                            ? avail - span
                                            : tail;
            }
          }
        }
      }
      mdbx_tassert(txn, chunk > 0);
  
      mdbx_trace("%s: rc_rid %" PRIaTXN ", reused_gc_slot %u, reservation-id "
                 "%" PRIaTXN,
                 dbg_prefix_mode, gc_rid, reused_gc_slot, reservation_gc_id);
  
      mdbx_trace("%s: chunk %u, gc-per-ovpage %u", dbg_prefix_mode, chunk,
                 env->me_maxgc_ov1page);
  
      mdbx_tassert(txn, reservation_gc_id < *env->me_oldest);
      if (unlikely(reservation_gc_id < 1 ||
                   reservation_gc_id >= *env->me_oldest)) {
        mdbx_error("%s", "** internal error (reservation_gc_id)");
        rc = MDBX_PROBLEM;
        goto bailout;
      }
  
      key.iov_len = sizeof(reservation_gc_id);
      key.iov_base = &reservation_gc_id;
      data.iov_len = (chunk + 1) * sizeof(pgno_t);
      mdbx_trace("%s.reserve: %u [%u...%u] @%" PRIaTXN, dbg_prefix_mode, chunk,
                 settled + 1, settled + chunk + 1, reservation_gc_id);
      mdbx_prep_backlog(txn, &couple.outer, data.iov_len);
      rc = mdbx_cursor_put(&couple.outer, &key, &data,
                           MDBX_RESERVE | MDBX_NOOVERWRITE);
      mdbx_tassert(txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist,
                                              txn->mt_next_pgno));
      if (unlikely(rc != MDBX_SUCCESS))
        goto bailout;
  
      clean_reserved_gc_pnl(env, data);
      settled += chunk;
      mdbx_trace("%s.settled %u (+%u), continue", dbg_prefix_mode, settled,
                 chunk);
  
      if (txn->tw.lifo_reclaimed &&
          unlikely(amount < MDBX_PNL_SIZE(txn->tw.reclaimed_pglist))) {
        mdbx_notice("** restart: reclaimed-list growth %u -> %u", amount,
                    (unsigned)MDBX_PNL_SIZE(txn->tw.reclaimed_pglist));
        goto retry_noaccount;
      }
  
      continue;
    }
  
    mdbx_tassert(
        txn,
        cleaned_gc_slot ==
            (txn->tw.lifo_reclaimed ? MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) : 0));
  
    mdbx_trace("%s", " >> filling");
    /* Fill in the reserved records */
    filled_gc_slot =
        txn->tw.lifo_reclaimed
            ? (unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed) - reused_gc_slot
            : reused_gc_slot;
    rc = MDBX_SUCCESS;
    mdbx_tassert(
        txn, mdbx_pnl_check4assert(txn->tw.reclaimed_pglist, txn->mt_next_pgno));
    mdbx_tassert(txn, mdbx_dirtylist_check(txn));
    if (MDBX_PNL_SIZE(txn->tw.reclaimed_pglist)) {
      MDBX_val key, data;
      key.iov_len = data.iov_len = 0; /* avoid MSVC warning */
      key.iov_base = data.iov_base = NULL;
  
      const unsigned amount = MDBX_PNL_SIZE(txn->tw.reclaimed_pglist);
      unsigned left = amount;
      if (txn->tw.lifo_reclaimed == nullptr) {
        mdbx_tassert(txn, lifo == 0);
        rc = mdbx_cursor_first(&couple.outer, &key, &data);
        if (unlikely(rc != MDBX_SUCCESS))
          goto bailout;
      } else {
        mdbx_tassert(txn, lifo != 0);
      }
  
      while (true) {
        txnid_t fill_gc_id;
        mdbx_trace("%s: left %u of %u", dbg_prefix_mode, left,
                   (unsigned)MDBX_PNL_SIZE(txn->tw.reclaimed_pglist));
        if (txn->tw.lifo_reclaimed == nullptr) {
          mdbx_tassert(txn, lifo == 0);
          fill_gc_id = unaligned_peek_u64(4, key.iov_base);
          if (filled_gc_slot-- == 0 || fill_gc_id > txn->tw.last_reclaimed) {
            mdbx_notice(
                "** restart: reserve depleted (filled_slot %u, fill_id %" PRIaTXN
                " > last_reclaimed %" PRIaTXN,
                filled_gc_slot, fill_gc_id, txn->tw.last_reclaimed);
            goto retry;
          }
        } else {
          mdbx_tassert(txn, lifo != 0);
          if (++filled_gc_slot >
              (unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed)) {
            mdbx_notice("** restart: reserve depleted (filled_gc_slot %u > "
                        "lifo_reclaimed %u" PRIaTXN,
                        filled_gc_slot,
                        (unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed));
            goto retry;
          }
          fill_gc_id = txn->tw.lifo_reclaimed[filled_gc_slot];
          mdbx_trace("%s.seek-reservation @%" PRIaTXN " at lifo_reclaimed[%u]",
                     dbg_prefix_mode, fill_gc_id, filled_gc_slot);
          key.iov_base = &fill_gc_id;
          key.iov_len = sizeof(fill_gc_id);
          rc = mdbx_cursor_get(&couple.outer, &key, &data, MDBX_SET_KEY);
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
        }
        mdbx_tassert(txn, cleaned_gc_slot ==
                              (txn->tw.lifo_reclaimed
                                   ? MDBX_PNL_SIZE(txn->tw.lifo_reclaimed)
                                   : 0));
        mdbx_tassert(txn, fill_gc_id > 0 && fill_gc_id < *env->me_oldest);
        key.iov_base = &fill_gc_id;
        key.iov_len = sizeof(fill_gc_id);
  
        mdbx_tassert(txn, data.iov_len >= sizeof(pgno_t) * 2);
        couple.outer.mc_flags |= C_GCFREEZE;
        unsigned chunk = (unsigned)(data.iov_len / sizeof(pgno_t)) - 1;
        if (unlikely(chunk > left)) {
          mdbx_trace("%s: chunk %u > left %u, @%" PRIaTXN, dbg_prefix_mode, chunk,
                     left, fill_gc_id);
          if ((loop < 5 && chunk - left > loop / 2) ||
              chunk - left > env->me_maxgc_ov1page) {
            data.iov_len = (left + 1) * sizeof(pgno_t);
            if (loop < 7)
              couple.outer.mc_flags &= ~C_GCFREEZE;
          }
          chunk = left;
        }
        rc = mdbx_cursor_put(&couple.outer, &key, &data,
                             MDBX_CURRENT | MDBX_RESERVE);
        couple.outer.mc_flags &= ~C_GCFREEZE;
        if (unlikely(rc != MDBX_SUCCESS))
          goto bailout;
        clean_reserved_gc_pnl(env, data);
  
        if (unlikely(txn->tw.loose_count ||
                     amount != MDBX_PNL_SIZE(txn->tw.reclaimed_pglist))) {
          mdbx_notice("** restart: reclaimed-list growth (%u -> %u, loose +%u)",
                      amount, MDBX_PNL_SIZE(txn->tw.reclaimed_pglist),
                      txn->tw.loose_count);
          goto retry;
        }
        if (unlikely(txn->tw.lifo_reclaimed
                         ? cleaned_gc_slot < MDBX_PNL_SIZE(txn->tw.lifo_reclaimed)
                         : cleaned_gc_id < txn->tw.last_reclaimed)) {
          mdbx_notice("%s", "** restart: reclaimed-slots changed");
          goto retry;
        }
  
        pgno_t *dst = data.iov_base;
        *dst++ = chunk;
        pgno_t *src = MDBX_PNL_BEGIN(txn->tw.reclaimed_pglist) + left - chunk;
        memcpy(dst, src, chunk * sizeof(pgno_t));
        pgno_t *from = src, *to = src + chunk;
        mdbx_trace("%s.fill: %u [ %u:%" PRIaPGNO "...%u:%" PRIaPGNO
                   "] @%" PRIaTXN,
                   dbg_prefix_mode, chunk,
                   (unsigned)(from - txn->tw.reclaimed_pglist), from[0],
                   (unsigned)(to - txn->tw.reclaimed_pglist), to[-1], fill_gc_id);
  
        left -= chunk;
        if (mdbx_audit_enabled()) {
          rc = mdbx_audit_ex(txn, retired_stored + amount - left, true);
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
        }
        if (left == 0) {
          rc = MDBX_SUCCESS;
          break;
        }
  
        if (txn->tw.lifo_reclaimed == nullptr) {
          mdbx_tassert(txn, lifo == 0);
          rc = mdbx_cursor_next(&couple.outer, &key, &data, MDBX_NEXT);
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
        } else {
          mdbx_tassert(txn, lifo != 0);
        }
      }
    }
  
    mdbx_tassert(txn, rc == MDBX_SUCCESS);
    if (unlikely(txn->tw.loose_count != 0 ||
                 filled_gc_slot !=
                     (txn->tw.lifo_reclaimed
                          ? (unsigned)MDBX_PNL_SIZE(txn->tw.lifo_reclaimed)
                          : 0))) {
      mdbx_notice("** restart: reserve excess (filled-slot %u, loose-count %u)",
                  filled_gc_slot, txn->tw.loose_count);
      goto retry;
    }
  
    mdbx_tassert(txn,
                 txn->tw.lifo_reclaimed == NULL ||
                     cleaned_gc_slot == MDBX_PNL_SIZE(txn->tw.lifo_reclaimed));
  
  bailout:
    txn->tw.cursors[FREE_DBI] = couple.outer.mc_next;
  
  bailout_notracking:
    MDBX_PNL_SIZE(txn->tw.reclaimed_pglist) = 0;
    mdbx_trace("<<< %u loops, rc = %d", loop, rc);
    return rc;
  }
  
  static int mdbx_flush_iov(MDBX_txn *const txn, struct iovec *iov,
                            unsigned iov_items, size_t iov_off,
                            size_t iov_bytes) {
    MDBX_env *const env = txn->mt_env;
    mdbx_assert(env, iov_items > 0);
    int rc;
    if (likely(iov_items == 1)) {
      mdbx_assert(env, iov->iov_len == iov_bytes);
      rc = mdbx_pwrite(env->me_lazy_fd, iov->iov_base, iov_bytes, iov_off);
    } else {
      rc = mdbx_pwritev(env->me_lazy_fd, iov, iov_items, iov_off, iov_bytes);
    }
  
    if (unlikely(rc != MDBX_SUCCESS)) {
      mdbx_error("Write error: %s", mdbx_strerror(rc));
      txn->mt_flags |= MDBX_TXN_ERROR;
    }
  
    for (unsigned i = 0; i < iov_items; i++)
      mdbx_dpage_free(env, (MDBX_page *)iov[i].iov_base,
                      bytes2pgno(env, iov[i].iov_len));
    return rc;
  }
  
  /* Flush (some) dirty pages to the map, after clearing their dirty flag.
   * [in] txn   the transaction that's being committed
   * [in] keep  number of initial pages in dirtylist to keep dirty.
   * Returns 0 on success, non-zero on failure. */
  __hot static int mdbx_page_flush(MDBX_txn *txn, const unsigned keep) {
    struct iovec iov[MDBX_COMMIT_PAGES];
    const MDBX_DPL dl = (keep || txn->tw.loose_count > 1)
                            ? mdbx_dpl_sort(txn->tw.dirtylist)
                            : txn->tw.dirtylist;
    MDBX_env *const env = txn->mt_env;
    pgno_t flush_begin = MAX_PAGENO;
    pgno_t flush_end = MIN_PAGENO;
    unsigned iov_items = 0;
    size_t iov_bytes = 0;
    size_t iov_off = 0;
    unsigned r, w;
    for (r = w = keep; ++r <= dl->length;) {
      MDBX_page *dp = dl[r].ptr;
      mdbx_tassert(txn,
                   dp->mp_pgno >= MIN_PAGENO && dp->mp_pgno < txn->mt_next_pgno);
      mdbx_tassert(txn, dp->mp_flags & P_DIRTY);
  
      /* Don't flush this page yet */
      if (dp->mp_flags & P_KEEP) {
        dp->mp_flags &= ~P_KEEP;
        dl[++w] = dl[r];
        continue;
      }
      if (dp->mp_flags & P_LOOSE) {
        dl[++w] = dl[r];
        continue;
      }
  
      const unsigned npages = IS_OVERFLOW(dp) ? dp->mp_pages : 1;
      flush_begin = (flush_begin < dp->mp_pgno) ? flush_begin : dp->mp_pgno;
      flush_end =
          (flush_end > dp->mp_pgno + npages) ? flush_end : dp->mp_pgno + npages;
      *env->me_unsynced_pages += npages;
      dp->mp_flags &= ~P_DIRTY;
      dp->mp_txnid = pp_txnid2chk(txn);
  
      if ((env->me_flags & MDBX_WRITEMAP) == 0) {
        const size_t size = pgno2bytes(env, npages);
        if (iov_off + iov_bytes != pgno2bytes(env, dp->mp_pgno) ||
            iov_items == ARRAY_LENGTH(iov) || iov_bytes + size > MAX_WRITE) {
          if (iov_items) {
            int rc = mdbx_flush_iov(txn, iov, iov_items, iov_off, iov_bytes);
            if (unlikely(rc != MDBX_SUCCESS))
              return rc;
  #if defined(__linux__) || defined(__gnu_linux__)
            if (mdbx_linux_kernel_version >= 0x02060b00)
            /* Linux kernels older than version 2.6.11 ignore the addr and nbytes
             * arguments, making this function fairly expensive. Therefore, the
             * whole cache is always flushed. */
  #endif /* Linux */
              mdbx_flush_incoherent_mmap(env->me_map + iov_off, iov_bytes,
                                         env->me_os_psize);
            iov_items = 0;
            iov_bytes = 0;
          }
          iov_off = pgno2bytes(env, dp->mp_pgno);
        }
        iov[iov_items].iov_base = (void *)dp;
        iov[iov_items].iov_len = size;
        iov_items += 1;
        iov_bytes += size;
      }
    }
  
    if (iov_items) {
      int rc = mdbx_flush_iov(txn, iov, iov_items, iov_off, iov_bytes);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  
  #if defined(__linux__) || defined(__gnu_linux__)
    if ((env->me_flags & MDBX_WRITEMAP) == 0 &&
        mdbx_linux_kernel_version < 0x02060b00)
      /* Linux kernels older than version 2.6.11 ignore the addr and nbytes
       * arguments, making this function fairly expensive. Therefore, the
       * whole cache is always flushed. */
      mdbx_flush_incoherent_mmap(env->me_map + pgno2bytes(env, flush_begin),
                                 pgno2bytes(env, flush_end - flush_begin),
                                 env->me_os_psize);
  #endif /* Linux */
  
    /* TODO: use flush_begin & flush_end for msync() & sync_file_range(). */
    (void)flush_begin;
    (void)flush_end;
  
    txn->tw.dirtyroom += r - 1 - w;
    dl->length = w;
    mdbx_tassert(txn, txn->mt_parent ||
                          txn->tw.dirtyroom + txn->tw.dirtylist->length ==
                              MDBX_DPL_TXNFULL);
    return MDBX_SUCCESS;
  }
  
  /* Check txn and dbi arguments to a function */
  static __always_inline bool mdbx_txn_dbi_exists(MDBX_txn *txn, MDBX_dbi dbi,
                                                  unsigned validity) {
    if (likely(dbi < txn->mt_numdbs && (txn->mt_dbistate[dbi] & validity)))
      return true;
  
    return dbi_import(txn, dbi);
  }
  
  int mdbx_txn_commit(MDBX_txn *txn) { return __inline_mdbx_txn_commit(txn); }
  
  int mdbx_txn_commit_ex(MDBX_txn *txn, MDBX_commit_latency *latency) {
    STATIC_ASSERT(MDBX_TXN_FINISHED ==
                  MDBX_TXN_BLOCKED - MDBX_TXN_HAS_CHILD - MDBX_TXN_ERROR);
    const uint64_t ts_0 = latency ? mdbx_osal_monotime() : 0;
    uint64_t ts_1 = 0, ts_2 = 0, ts_3 = 0, ts_4 = 0;
    uint32_t audit_duration = 0;
  
    int rc = check_txn(txn, MDBX_TXN_FINISHED);
    if (unlikely(rc != MDBX_SUCCESS))
      goto provide_latency;
  
    if (unlikely(txn->mt_flags & MDBX_TXN_ERROR)) {
      rc = MDBX_RESULT_TRUE;
      goto fail;
    }
  
    MDBX_env *env = txn->mt_env;
  #if MDBX_ENV_CHECKPID
    if (unlikely(env->me_pid != mdbx_getpid())) {
      env->me_flags |= MDBX_FATAL_ERROR;
      rc = MDBX_PANIC;
      goto provide_latency;
    }
  #endif /* MDBX_ENV_CHECKPID */
  
    /* mdbx_txn_end() mode for a commit which writes nothing */
    unsigned end_mode =
        MDBX_END_EMPTY_COMMIT | MDBX_END_UPDATE | MDBX_END_SLOT | MDBX_END_FREE;
    if (unlikely(F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)))
      goto done;
  
    if (txn->mt_child) {
      rc = mdbx_txn_commit_ex(txn->mt_child, NULL);
      mdbx_tassert(txn, txn->mt_child == NULL);
      if (unlikely(rc != MDBX_SUCCESS))
        goto fail;
    }
  
    if (unlikely(txn != env->me_txn)) {
      mdbx_debug("%s", "attempt to commit unknown transaction");
      rc = MDBX_EINVAL;
      goto fail;
    }
  
    if (txn->mt_parent) {
      mdbx_assert(env, txn != env->me_txn0);
      MDBX_txn *const parent = txn->mt_parent;
      mdbx_assert(env, parent->mt_signature == MDBX_MT_SIGNATURE);
      mdbx_assert(env, parent->mt_child == txn &&
                           (parent->mt_flags & MDBX_TXN_HAS_CHILD) != 0);
      mdbx_assert(env, mdbx_dirtylist_check(txn));
  
      if (txn->tw.dirtylist->length == 0 &&
          (txn->mt_flags & (MDBX_TXN_DIRTY | MDBX_TXN_SPILLS)) == 0 &&
          parent->mt_numdbs == txn->mt_numdbs) {
        for (int i = txn->mt_numdbs; --i >= 0;) {
          mdbx_tassert(txn, (txn->mt_dbistate[i] & DBI_DIRTY) == 0);
          if ((txn->mt_dbistate[i] & DBI_STALE) &&
              !(parent->mt_dbistate[i] & DBI_STALE))
            mdbx_tassert(txn, memcmp(&parent->mt_dbs[i], &txn->mt_dbs[i],
                                     sizeof(MDBX_db)) == 0);
        }
  
        mdbx_tassert(txn, memcmp(&parent->mt_geo, &txn->mt_geo,
                                 sizeof(parent->mt_geo)) == 0);
        mdbx_tassert(txn, memcmp(&parent->mt_canary, &txn->mt_canary,
                                 sizeof(parent->mt_canary)) == 0);
  
        end_mode = MDBX_END_ABORT | MDBX_END_SLOT | MDBX_END_FREE;
        goto done;
      }
  
      /* Preserve space for spill list to avoid parent's state corruption
       * if allocation fails. */
      if (txn->tw.spill_pages && parent->tw.spill_pages) {
        rc = mdbx_pnl_need(&parent->tw.spill_pages,
                           MDBX_PNL_SIZE(txn->tw.spill_pages));
        if (unlikely(rc != MDBX_SUCCESS))
          goto fail;
      }
  
      //-------------------------------------------------------------------------
  
      parent->tw.lifo_reclaimed = txn->tw.lifo_reclaimed;
      txn->tw.lifo_reclaimed = NULL;
  
      parent->tw.retired_pages = txn->tw.retired_pages;
      txn->tw.retired_pages = NULL;
  
      mdbx_pnl_free(parent->tw.reclaimed_pglist);
      parent->tw.reclaimed_pglist = txn->tw.reclaimed_pglist;
      txn->tw.reclaimed_pglist = NULL;
      parent->tw.last_reclaimed = txn->tw.last_reclaimed;
  
      parent->mt_geo = txn->mt_geo;
      parent->mt_canary = txn->mt_canary;
      parent->mt_flags |= txn->mt_flags & MDBX_TXN_DIRTY;
  
      /* Merge our cursors into parent's and close them */
      mdbx_cursors_eot(txn, true);
      end_mode |= MDBX_END_EOTDONE;
  
      /* Update parent's DB table. */
      memcpy(parent->mt_dbs, txn->mt_dbs, txn->mt_numdbs * sizeof(MDBX_db));
      parent->mt_numdbs = txn->mt_numdbs;
      parent->mt_dbistate[FREE_DBI] = txn->mt_dbistate[FREE_DBI];
      parent->mt_dbistate[MAIN_DBI] = txn->mt_dbistate[MAIN_DBI];
      for (unsigned i = CORE_DBS; i < txn->mt_numdbs; i++) {
        /* preserve parent's DB_NEW status */
        parent->mt_dbistate[i] = txn->mt_dbistate[i] | (parent->mt_dbistate[i] &
                                                        (DBI_CREAT | DBI_FRESH));
      }
      ts_1 = latency ? mdbx_osal_monotime() : 0;
  
      /* Remove refunded pages from parent's dirty & spill lists */
      MDBX_DPL dst = mdbx_dpl_sort(parent->tw.dirtylist);
      while (dst->length && dst[dst->length].pgno >= parent->mt_next_pgno) {
        MDBX_page *mp = dst[dst->length].ptr;
        if (mp && (txn->mt_env->me_flags & MDBX_WRITEMAP) == 0)
          mdbx_dpage_free(txn->mt_env, mp, IS_OVERFLOW(mp) ? mp->mp_pages : 1);
        dst->length -= 1;
      }
      parent->tw.dirtyroom += dst->sorted - dst->length;
      dst->sorted = dst->length;
      mdbx_tassert(parent,
                   parent->mt_parent ||
                       parent->tw.dirtyroom + parent->tw.dirtylist->length ==
                           MDBX_DPL_TXNFULL);
  
      if (parent->tw.spill_pages && MDBX_PNL_SIZE(parent->tw.spill_pages) > 0 &&
          MDBX_PNL_MOST(parent->tw.spill_pages) >= parent->mt_next_pgno << 1) {
        const MDBX_PNL ps = parent->tw.spill_pages;
  #if MDBX_PNL_ASCENDING
        unsigned i = MDBX_PNL_SIZE(ps);
        assert(MDBX_PNL_MOST(ps) == MDBX_PNL_LAST(ps));
        do
          i -= 1;
        while (i && ps[i] >= parent->mt_next_pgno << 1);
        MDBX_PNL_SIZE(ps) = i;
  #else
        assert(MDBX_PNL_MOST(ps) == MDBX_PNL_FIRST(ps));
        unsigned i = 1, len = MDBX_PNL_SIZE(ps);
        while (i < len && ps[i + 1] >= parent->mt_next_pgno << 1)
          ++i;
        MDBX_PNL_SIZE(ps) = len -= i;
        for (unsigned k = 1; k <= len; ++k)
          ps[k] = ps[k + i];
  #endif
      }
  
      /* Remove anything in our dirty list from parent's spill list */
      MDBX_DPL src = mdbx_dpl_sort(txn->tw.dirtylist);
      if (likely(src->length > 0) && parent->tw.spill_pages &&
          MDBX_PNL_SIZE(parent->tw.spill_pages) > 0) {
        MDBX_PNL sp = parent->tw.spill_pages;
        assert(mdbx_pnl_check4assert(sp, txn->mt_next_pgno));
  
        const unsigned len = MDBX_PNL_SIZE(parent->tw.spill_pages);
        MDBX_PNL_SIZE(sp) = ~(pgno_t)0;
  
        /* Mark our dirty pages as deleted in parent spill list */
        unsigned r, w, i = 1;
        w = r = len;
        do {
          pgno_t pn = src[i].pgno << 1;
          while (pn > sp[r])
            r--;
          if (pn == sp[r]) {
            sp[r] = 1;
            w = --r;
          }
        } while (++i <= src->length);
  
        /* Squash deleted pagenums if we deleted any */
        for (r = w; ++r <= len;)
          if ((sp[r] & 1) == 0)
            sp[++w] = sp[r];
        MDBX_PNL_SIZE(sp) = w;
        assert(mdbx_pnl_check4assert(sp, txn->mt_next_pgno << 1));
      }
  
      /* Remove anything in our spill list from parent's dirty list */
      if (txn->tw.spill_pages && MDBX_PNL_SIZE(txn->tw.spill_pages) > 0) {
        const MDBX_PNL sp = txn->tw.spill_pages;
        mdbx_pnl_sort(sp);
        /* Scanning in ascend order */
        const int step = MDBX_PNL_ASCENDING ? 1 : -1;
        const int begin = MDBX_PNL_ASCENDING ? 1 : MDBX_PNL_SIZE(sp);
        const int end = MDBX_PNL_ASCENDING ? MDBX_PNL_SIZE(sp) + 1 : 0;
        mdbx_tassert(txn, sp[begin] <= sp[end - step]);
  
        unsigned r, w = r = mdbx_dpl_search(dst, sp[begin] >> 1);
        mdbx_tassert(txn, dst->sorted == dst->length);
        for (int i = begin; r <= dst->length;) {
          mdbx_tassert(txn, (sp[i] & 1) == 0);
          const pgno_t pgno = sp[i] >> 1;
          if (dst[r].pgno < pgno) {
            dst[w++] = dst[r++];
          } else if (dst[r].pgno > pgno) {
            i += step;
            if (i == end)
              while (r <= dst->length)
                dst[w++] = dst[r++];
          } else {
            MDBX_page *dp = dst[r++].ptr;
            if ((env->me_flags & MDBX_WRITEMAP) == 0)
              mdbx_dpage_free(env, dp, IS_OVERFLOW(dp) ? dp->mp_pages : 1);
          }
        }
        mdbx_tassert(txn, r == dst->length + 1);
        dst->length = w;
        parent->tw.dirtyroom += r - w;
      }
      assert(dst->sorted == dst->length);
      mdbx_tassert(parent,
                   parent->mt_parent ||
                       parent->tw.dirtyroom + parent->tw.dirtylist->length ==
                           MDBX_DPL_TXNFULL);
  
      unsigned d, s, l;
      /* Find length of merging our dirty list with parent's */
      for (l = 0, d = dst->length, s = src->length; d > 0 && s > 0; ++l) {
        const pgno_t s_pgno = src[s].pgno;
        const pgno_t d_pgno = dst[d].pgno;
        d -= d_pgno >= s_pgno;
        s -= d_pgno <= s_pgno;
      }
      assert(dst->sorted == dst->length);
      dst->sorted = l += d + s;
      assert(dst->sorted >= dst->length);
      parent->tw.dirtyroom -= dst->sorted - dst->length;
  
      /* Merge our dirty list into parent's */
      for (d = dst->length, s = src->length; d > 0 && s > 0; --l) {
        if (dst[d].pgno > src[s].pgno)
          dst[l] = dst[d--];
        else if (dst[d].pgno < src[s].pgno)
          dst[l] = src[s--];
        else {
          MDBX_page *dp = dst[d--].ptr;
          if (dp && (env->me_flags & MDBX_WRITEMAP) == 0)
            mdbx_dpage_free(env, dp, IS_OVERFLOW(dp) ? dp->mp_pgno : 1);
          dst[l] = src[s--];
        }
      }
      if (s) {
        do
          dst[l--] = src[s--];
        while (s > 0);
      } else if (d) {
        do
          dst[l--] = dst[d--];
        while (d > 0);
      }
      assert(l == 0);
      dst->length = dst->sorted;
      mdbx_free(txn->tw.dirtylist);
      txn->tw.dirtylist = nullptr;
      mdbx_tassert(parent,
                   parent->mt_parent ||
                       parent->tw.dirtyroom + parent->tw.dirtylist->length ==
                           MDBX_DPL_TXNFULL);
  
      if (txn->tw.spill_pages) {
        if (parent->tw.spill_pages) {
          /* Must not fail since space was preserved above. */
          rc = mdbx_pnl_append_list(&parent->tw.spill_pages, txn->tw.spill_pages);
          mdbx_assert(env, rc == MDBX_SUCCESS);
          (void)rc;
          mdbx_pnl_free(txn->tw.spill_pages);
          mdbx_pnl_sort(parent->tw.spill_pages);
        } else {
          parent->tw.spill_pages = txn->tw.spill_pages;
        }
      }
  
      parent->mt_flags &= ~(MDBX_TXN_SPILLS | MDBX_TXN_HAS_CHILD);
      if (parent->tw.spill_pages) {
        assert(mdbx_pnl_check4assert(parent->tw.spill_pages,
                                     parent->mt_next_pgno << 1));
        if (MDBX_PNL_SIZE(parent->tw.spill_pages))
          parent->mt_flags |= MDBX_TXN_SPILLS;
      }
  
      ts_2 = latency ? mdbx_osal_monotime() : 0;
      /* Append our loose page list to parent's */
      if (txn->tw.loose_pages) {
        MDBX_page **lp = &parent->tw.loose_pages;
        while (*lp)
          lp = &(*lp)->mp_next;
        *lp = txn->tw.loose_pages;
        parent->tw.loose_count += txn->tw.loose_count;
      }
      if (txn->tw.retired2parent_pages) {
        MDBX_page *mp = txn->tw.retired2parent_pages;
        do {
          MDBX_page *next = mp->mp_next;
          rc = mdbx_page_loose(parent, mp);
          if (unlikely(rc != MDBX_SUCCESS))
            goto fail;
          mp = next;
        } while (mp);
      }
  
      env->me_txn = parent;
      parent->mt_child = NULL;
      mdbx_tassert(parent, mdbx_dirtylist_check(parent));
  
      /* Scan parent's loose page for suitable for refund */
      for (MDBX_page *mp = parent->tw.loose_pages; mp; mp = mp->mp_next) {
        if (mp->mp_pgno == parent->mt_next_pgno - 1) {
          mdbx_refund(parent);
          break;
        }
      }
  
      ts_4 = ts_3 = latency ? mdbx_osal_monotime() : 0;
      txn->mt_signature = 0;
      mdbx_free(txn);
      mdbx_tassert(parent, mdbx_dirtylist_check(parent));
      rc = MDBX_SUCCESS;
      goto provide_latency;
    }
  
    mdbx_tassert(txn, txn->tw.dirtyroom + txn->tw.dirtylist->length ==
                          MDBX_DPL_TXNFULL);
    mdbx_cursors_eot(txn, false);
    end_mode |= MDBX_END_EOTDONE;
  
    if (txn->tw.dirtylist->length == 0 &&
        (txn->mt_flags & (MDBX_TXN_DIRTY | MDBX_TXN_SPILLS)) == 0) {
      for (int i = txn->mt_numdbs; --i >= 0;)
        mdbx_tassert(txn, (txn->mt_dbistate[i] & DBI_DIRTY) == 0);
      rc = MDBX_SUCCESS;
      goto done;
    }
  
    mdbx_debug("committing txn %" PRIaTXN " %p on mdbenv %p, root page %" PRIaPGNO
               "/%" PRIaPGNO,
               txn->mt_txnid, (void *)txn, (void *)env,
               txn->mt_dbs[MAIN_DBI].md_root, txn->mt_dbs[FREE_DBI].md_root);
  
    /* Update DB root pointers */
    if (txn->mt_numdbs > CORE_DBS) {
      MDBX_cursor_couple couple;
      MDBX_val data;
      data.iov_len = sizeof(MDBX_db);
  
      rc = mdbx_cursor_init(&couple.outer, txn, MAIN_DBI);
      if (unlikely(rc != MDBX_SUCCESS))
        goto fail;
      for (MDBX_dbi i = CORE_DBS; i < txn->mt_numdbs; i++) {
        if (txn->mt_dbistate[i] & DBI_DIRTY) {
          if (unlikely(TXN_DBI_CHANGED(txn, i))) {
            rc = MDBX_BAD_DBI;
            goto fail;
          }
          MDBX_db *db = &txn->mt_dbs[i];
          db->md_mod_txnid = pp_txnid2chk(txn);
          data.iov_base = db;
          WITH_CURSOR_TRACKING(couple.outer,
                               rc = mdbx_cursor_put(&couple.outer,
                                                    &txn->mt_dbxs[i].md_name,
                                                    &data, F_SUBDATA));
          if (unlikely(rc != MDBX_SUCCESS))
            goto fail;
        }
      }
    }
  
    ts_1 = latency ? mdbx_osal_monotime() : 0;
    rc = mdbx_update_gc(txn);
    if (unlikely(rc != MDBX_SUCCESS))
      goto fail;
  
    ts_2 = latency ? mdbx_osal_monotime() : 0;
    if (mdbx_audit_enabled()) {
      rc = mdbx_audit_ex(txn, MDBX_PNL_SIZE(txn->tw.retired_pages), true);
      const uint64_t audit_end = mdbx_osal_monotime();
      audit_duration = mdbx_osal_monotime_to_16dot16(audit_end - ts_2);
      ts_2 = audit_end;
      if (unlikely(rc != MDBX_SUCCESS))
        goto fail;
    }
  
    rc = mdbx_page_flush(txn, 0);
    ts_3 = latency ? mdbx_osal_monotime() : 0;
    if (likely(rc == MDBX_SUCCESS)) {
      if (txn->mt_dbs[MAIN_DBI].md_flags & DBI_DIRTY)
        txn->mt_dbs[MAIN_DBI].md_mod_txnid = pp_txnid2chk(txn);
  
      MDBX_meta meta, *head = mdbx_meta_head(env);
      meta.mm_magic_and_version = head->mm_magic_and_version;
      meta.mm_extra_flags = head->mm_extra_flags;
      meta.mm_validator_id = head->mm_validator_id;
      meta.mm_extra_pagehdr = head->mm_extra_pagehdr;
      meta.mm_pages_retired =
          head->mm_pages_retired + MDBX_PNL_SIZE(txn->tw.retired_pages);
  
      meta.mm_geo = txn->mt_geo;
      meta.mm_dbs[FREE_DBI] = txn->mt_dbs[FREE_DBI];
      meta.mm_dbs[MAIN_DBI] = txn->mt_dbs[MAIN_DBI];
      meta.mm_canary = txn->mt_canary;
      mdbx_meta_set_txnid(env, &meta, txn->mt_txnid);
  
      rc = mdbx_sync_locked(
          env, env->me_flags | txn->mt_flags | MDBX_SHRINK_ALLOWED, &meta);
    }
    ts_4 = latency ? mdbx_osal_monotime() : 0;
    if (unlikely(rc != MDBX_SUCCESS)) {
      env->me_flags |= MDBX_FATAL_ERROR;
      goto fail;
    }
  
    end_mode = MDBX_END_COMMITTED | MDBX_END_UPDATE | MDBX_END_EOTDONE;
  
  done:
    rc = mdbx_txn_end(txn, end_mode);
  
  provide_latency:
    if (latency) {
      latency->audit = audit_duration;
      latency->preparation =
          ts_1 ? mdbx_osal_monotime_to_16dot16(ts_1 - ts_0) : 0;
      latency->gc =
          (ts_1 && ts_2) ? mdbx_osal_monotime_to_16dot16(ts_2 - ts_1) : 0;
      latency->write =
          (ts_2 && ts_3) ? mdbx_osal_monotime_to_16dot16(ts_3 - ts_2) : 0;
      latency->sync =
          (ts_3 && ts_4) ? mdbx_osal_monotime_to_16dot16(ts_4 - ts_3) : 0;
      const uint64_t ts_5 = mdbx_osal_monotime();
      latency->ending = ts_4 ? mdbx_osal_monotime_to_16dot16(ts_5 - ts_4) : 0;
      latency->whole = mdbx_osal_monotime_to_16dot16(ts_5 - ts_0);
    }
    return rc;
  
  fail:
    mdbx_txn_abort(txn);
    goto provide_latency;
  }
  
  static __cold int
  mdbx_validate_meta(MDBX_env *env, MDBX_meta *const meta, uint64_t *filesize,
                     const MDBX_page *const page, const unsigned meta_number,
                     MDBX_meta *dest, const unsigned guess_pagesize) {
    if (meta->mm_magic_and_version != MDBX_DATA_MAGIC &&
        meta->mm_magic_and_version != MDBX_DATA_MAGIC_DEVEL) {
      mdbx_error("meta[%u] has invalid magic/version %" PRIx64, meta_number,
                 meta->mm_magic_and_version);
      return ((meta->mm_magic_and_version >> 8) != MDBX_MAGIC)
                 ? MDBX_INVALID
                 : MDBX_VERSION_MISMATCH;
    }
  
    if (page->mp_pgno != meta_number) {
      mdbx_error("meta[%u] has invalid pageno %" PRIaPGNO, meta_number,
                 page->mp_pgno);
      return MDBX_INVALID;
    }
  
    if (page->mp_flags != P_META) {
      mdbx_error("page #%u not a meta-page", meta_number);
      return MDBX_INVALID;
    }
  
    /* LY: check pagesize */
    if (!is_powerof2(meta->mm_psize) || meta->mm_psize < MIN_PAGESIZE ||
        meta->mm_psize > MAX_PAGESIZE) {
      mdbx_warning("meta[%u] has invalid pagesize (%u), skip it", meta_number,
                   meta->mm_psize);
      return is_powerof2(meta->mm_psize) ? MDBX_VERSION_MISMATCH : MDBX_INVALID;
    }
  
    if (dest && meta_number == 0 && guess_pagesize != meta->mm_psize) {
      dest->mm_psize = meta->mm_psize;
      mdbx_verbose("meta[%u] took pagesize %u", meta_number, meta->mm_psize);
    }
  
    if (safe64_read(&meta->mm_txnid_a) != safe64_read(&meta->mm_txnid_b)) {
      mdbx_warning("meta[%u] not completely updated, skip it", meta_number);
      return MDBX_RESULT_TRUE;
    }
  
    /* LY: check signature as a checksum */
    if (META_IS_STEADY(meta) && meta->mm_datasync_sign != mdbx_meta_sign(meta)) {
      mdbx_warning("meta[%u] has invalid steady-checksum (0x%" PRIx64
                   " != 0x%" PRIx64 "), skip it",
                   meta_number, meta->mm_datasync_sign, mdbx_meta_sign(meta));
      return MDBX_RESULT_TRUE;
    }
  
    mdbx_debug("read meta%" PRIaPGNO " = root %" PRIaPGNO "/%" PRIaPGNO
               ", geo %" PRIaPGNO "/%" PRIaPGNO "-%" PRIaPGNO "/%" PRIaPGNO
               " +%u -%u, txn_id %" PRIaTXN ", %s",
               page->mp_pgno, meta->mm_dbs[MAIN_DBI].md_root,
               meta->mm_dbs[FREE_DBI].md_root, meta->mm_geo.lower,
               meta->mm_geo.next, meta->mm_geo.now, meta->mm_geo.upper,
               meta->mm_geo.grow, meta->mm_geo.shrink,
               meta->mm_txnid_a.inconsistent, mdbx_durable_str(meta));
  
    /* LY: check min-pages value */
    if (meta->mm_geo.lower < MIN_PAGENO || meta->mm_geo.lower > MAX_PAGENO) {
      mdbx_warning("meta[%u] has invalid min-pages (%" PRIaPGNO "), skip it",
                   meta_number, meta->mm_geo.lower);
      return MDBX_INVALID;
    }
  
    /* LY: check max-pages value */
    if (meta->mm_geo.upper < MIN_PAGENO || meta->mm_geo.upper > MAX_PAGENO ||
        meta->mm_geo.upper < meta->mm_geo.lower) {
      mdbx_warning("meta[%u] has invalid max-pages (%" PRIaPGNO "), skip it",
                   meta_number, meta->mm_geo.upper);
      return MDBX_INVALID;
    }
  
    /* LY: check last_pgno */
    if (meta->mm_geo.next < MIN_PAGENO || meta->mm_geo.next - 1 > MAX_PAGENO) {
      mdbx_warning("meta[%u] has invalid next-pageno (%" PRIaPGNO "), skip it",
                   meta_number, meta->mm_geo.next);
      return MDBX_CORRUPTED;
    }
  
    /* LY: check filesize & used_bytes */
    const uint64_t used_bytes = meta->mm_geo.next * (uint64_t)meta->mm_psize;
    if (used_bytes > *filesize) {
      /* Here could be a race with DB-shrinking performed by other process */
      int err = mdbx_filesize(env->me_lazy_fd, filesize);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
      if (used_bytes > *filesize) {
        mdbx_warning("meta[%u] used-bytes (%" PRIu64 ") beyond filesize (%" PRIu64
                     "), skip it",
                     meta_number, used_bytes, *filesize);
        return MDBX_CORRUPTED;
      }
    }
    if (meta->mm_geo.next - 1 > MAX_PAGENO || used_bytes > MAX_MAPSIZE) {
      mdbx_warning("meta[%u] has too large used-space (%" PRIu64 "), skip it",
                   meta_number, used_bytes);
      return MDBX_TOO_LARGE;
    }
  
    /* LY: check mapsize limits */
    const uint64_t mapsize_min = meta->mm_geo.lower * (uint64_t)meta->mm_psize;
    STATIC_ASSERT(MAX_MAPSIZE < PTRDIFF_MAX - MAX_PAGESIZE);
    STATIC_ASSERT(MIN_MAPSIZE < MAX_MAPSIZE);
    if (mapsize_min < MIN_MAPSIZE || mapsize_min > MAX_MAPSIZE) {
      if (MAX_MAPSIZE != MAX_MAPSIZE64 && mapsize_min > MAX_MAPSIZE &&
          mapsize_min <= MAX_MAPSIZE64) {
        mdbx_assert(env, meta->mm_geo.next - 1 <= MAX_PAGENO &&
                             used_bytes <= MAX_MAPSIZE);
        mdbx_warning("meta[%u] has too large min-mapsize (%" PRIu64 "), "
                     "but size of used space still acceptable (%" PRIu64 ")",
                     meta_number, mapsize_min, used_bytes);
        meta->mm_geo.lower = (pgno_t)(MAX_MAPSIZE / meta->mm_psize);
      } else {
        mdbx_warning("meta[%u] has invalid min-mapsize (%" PRIu64 "), skip it",
                     meta_number, mapsize_min);
        return MDBX_VERSION_MISMATCH;
      }
    }
  
    const uint64_t mapsize_max = meta->mm_geo.upper * (uint64_t)meta->mm_psize;
    STATIC_ASSERT(MIN_MAPSIZE < MAX_MAPSIZE);
    if (mapsize_max > MAX_MAPSIZE ||
        MAX_PAGENO < ceil_powerof2((size_t)mapsize_max, env->me_os_psize) /
                         (size_t)meta->mm_psize) {
      /* allow to open large DB from a 32-bit environment */
      mdbx_assert(env, meta->mm_geo.next - 1 <= MAX_PAGENO &&
                           used_bytes <= MAX_MAPSIZE);
      mdbx_warning("meta[%u] has too large max-mapsize (%" PRIu64 "), "
                   "but size of used space still acceptable (%" PRIu64 ")",
                   meta_number, mapsize_max, used_bytes);
      meta->mm_geo.upper = (pgno_t)(MAX_MAPSIZE / meta->mm_psize);
    }
  
    /* LY: check and silently put mm_geo.now into [geo.lower...geo.upper].
     *
     * Copy-with-compaction by previous version of libmdbx could produce DB-file
     * less than meta.geo.lower bound, in case actual filling is low or no data
     * at all. This is not a problem as there is no damage or loss of data.
     * Therefore it is better not to consider such situation as an error, but
     * silently correct it. */
    if (meta->mm_geo.now < meta->mm_geo.lower)
      meta->mm_geo.now = meta->mm_geo.lower;
    if (meta->mm_geo.now > meta->mm_geo.upper &&
        meta->mm_geo.next <= meta->mm_geo.upper)
      meta->mm_geo.now = meta->mm_geo.upper;
  
    if (meta->mm_geo.next > meta->mm_geo.now) {
      mdbx_warning("meta[%u] next-pageno (%" PRIaPGNO
                   ") is beyond end-pgno (%" PRIaPGNO "), skip it",
                   meta_number, meta->mm_geo.next, meta->mm_geo.now);
      return MDBX_CORRUPTED;
    }
  
    /* LY: GC root */
    if (meta->mm_dbs[FREE_DBI].md_root == P_INVALID) {
      if (meta->mm_dbs[FREE_DBI].md_branch_pages ||
          meta->mm_dbs[FREE_DBI].md_depth || meta->mm_dbs[FREE_DBI].md_entries ||
          meta->mm_dbs[FREE_DBI].md_leaf_pages ||
          meta->mm_dbs[FREE_DBI].md_overflow_pages) {
        mdbx_warning("meta[%u] has false-empty GC, skip it", meta_number);
        return MDBX_CORRUPTED;
      }
    } else if (meta->mm_dbs[FREE_DBI].md_root >= meta->mm_geo.next) {
      mdbx_warning("meta[%u] has invalid GC-root %" PRIaPGNO ", skip it",
                   meta_number, meta->mm_dbs[FREE_DBI].md_root);
      return MDBX_CORRUPTED;
    }
  
    /* LY: MainDB root */
    if (meta->mm_dbs[MAIN_DBI].md_root == P_INVALID) {
      if (meta->mm_dbs[MAIN_DBI].md_branch_pages ||
          meta->mm_dbs[MAIN_DBI].md_depth || meta->mm_dbs[MAIN_DBI].md_entries ||
          meta->mm_dbs[MAIN_DBI].md_leaf_pages ||
          meta->mm_dbs[MAIN_DBI].md_overflow_pages) {
        mdbx_warning("meta[%u] has false-empty maindb", meta_number);
        return MDBX_CORRUPTED;
      }
    } else if (meta->mm_dbs[MAIN_DBI].md_root >= meta->mm_geo.next) {
      mdbx_warning("meta[%u] has invalid maindb-root %" PRIaPGNO ", skip it",
                   meta_number, meta->mm_dbs[MAIN_DBI].md_root);
      return MDBX_CORRUPTED;
    }
  
    if (safe64_read(&meta->mm_txnid_a) == 0) {
      mdbx_warning("meta[%u] has zero txnid, skip it", meta_number);
      return MDBX_RESULT_TRUE;
    }
  
    return MDBX_SUCCESS;
  }
  
  /* Read the environment parameters of a DB environment
   * before mapping it into memory. */
  static __cold int mdbx_read_header(MDBX_env *env, MDBX_meta *dest,
                                     uint64_t *filesize,
                                     const int lck_exclusive) {
    int rc = mdbx_filesize(env->me_lazy_fd, filesize);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    memset(dest, 0, sizeof(MDBX_meta));
    dest->mm_datasync_sign = MDBX_DATASIGN_WEAK;
    rc = MDBX_CORRUPTED;
  
    /* Read twice all meta pages so we can find the latest one. */
    unsigned loop_limit = NUM_METAS * 2;
    for (unsigned loop_count = 0; loop_count < loop_limit; ++loop_count) {
      /* We don't know the page size on first time.
       * So, just guess it. */
      unsigned guess_pagesize = dest->mm_psize;
      if (guess_pagesize == 0)
        guess_pagesize =
            (loop_count > NUM_METAS) ? env->me_psize : env->me_os_psize;
  
      const unsigned meta_number = loop_count % NUM_METAS;
      const unsigned offset = guess_pagesize * meta_number;
  
      char buffer[MIN_PAGESIZE];
      unsigned retryleft = 42;
      while (1) {
        mdbx_trace("reading meta[%d]: offset %u, bytes %u, retry-left %u",
                   meta_number, offset, MIN_PAGESIZE, retryleft);
        int err = mdbx_pread(env->me_lazy_fd, buffer, MIN_PAGESIZE, offset);
        if (err != MDBX_SUCCESS) {
          if (err == MDBX_ENODATA && offset == 0 && loop_count == 0 &&
              *filesize == 0 && (env->me_flags & MDBX_RDONLY) == 0)
            mdbx_warning("read meta: empty file (%d, %s)", err,
                         mdbx_strerror(err));
          else
            mdbx_error("read meta[%u,%u]: %i, %s", offset, MIN_PAGESIZE, err,
                       mdbx_strerror(err));
          return err;
        }
  
        char again[MIN_PAGESIZE];
        err = mdbx_pread(env->me_lazy_fd, again, MIN_PAGESIZE, offset);
        if (err != MDBX_SUCCESS) {
          mdbx_error("read meta[%u,%u]: %i, %s", offset, MIN_PAGESIZE, err,
                     mdbx_strerror(err));
          return err;
        }
  
        if (memcmp(buffer, again, MIN_PAGESIZE) == 0 || --retryleft == 0)
          break;
  
        mdbx_verbose("meta[%u] was updated, re-read it", meta_number);
      }
  
      if (!retryleft) {
        mdbx_error("meta[%u] is too volatile, skip it", meta_number);
        continue;
      }
  
      MDBX_page *const page = (MDBX_page *)buffer;
      MDBX_meta *const meta = page_meta(page);
      rc = mdbx_validate_meta(env, meta, filesize, page, meta_number, dest,
                              guess_pagesize);
      if (rc != MDBX_SUCCESS)
        continue;
  
      if ((env->me_stuck_meta < 0)
              ? mdbx_meta_ot(prefer_steady, env, dest, meta)
              : (meta_number == (unsigned)env->me_stuck_meta)) {
        *dest = *meta;
        if (!META_IS_STEADY(dest))
          loop_limit += 1; /* LY: should re-read to hush race with update */
        mdbx_verbose("latch meta[%u]", meta_number);
      }
    }
  
    if (dest->mm_psize == 0 ||
        ((env->me_stuck_meta < 0)
             ? (!META_IS_STEADY(dest) &&
                !meta_weak_acceptable(env, dest, lck_exclusive))
             : false)) {
      mdbx_error("%s", "no usable meta-pages, database is corrupted");
      if (rc == MDBX_SUCCESS) {
        /* TODO: try to restore the database by fully checking b-tree structure
         * for the each meta page, if the corresponding option was given */
        return MDBX_CORRUPTED;
      }
      return rc;
    }
  
    return MDBX_SUCCESS;
  }
  
  static MDBX_page *__cold mdbx_meta_model(const MDBX_env *env, MDBX_page *model,
                                           unsigned num) {
  
    mdbx_ensure(env, is_powerof2(env->me_psize));
    mdbx_ensure(env, env->me_psize >= MIN_PAGESIZE);
    mdbx_ensure(env, env->me_psize <= MAX_PAGESIZE);
    mdbx_ensure(env, env->me_dbgeo.lower >= MIN_MAPSIZE);
    mdbx_ensure(env, env->me_dbgeo.upper <= MAX_MAPSIZE);
    mdbx_ensure(env, env->me_dbgeo.now >= env->me_dbgeo.lower);
    mdbx_ensure(env, env->me_dbgeo.now <= env->me_dbgeo.upper);
  
    memset(model, 0, sizeof(*model));
    model->mp_pgno = num;
    model->mp_flags = P_META;
    MDBX_meta *const model_meta = page_meta(model);
    model_meta->mm_magic_and_version = MDBX_DATA_MAGIC;
  
    model_meta->mm_geo.lower = bytes2pgno(env, env->me_dbgeo.lower);
    model_meta->mm_geo.upper = bytes2pgno(env, env->me_dbgeo.upper);
    model_meta->mm_geo.grow = (uint16_t)bytes2pgno(env, env->me_dbgeo.grow);
    model_meta->mm_geo.shrink = (uint16_t)bytes2pgno(env, env->me_dbgeo.shrink);
    model_meta->mm_geo.now = bytes2pgno(env, env->me_dbgeo.now);
    model_meta->mm_geo.next = NUM_METAS;
  
    mdbx_ensure(env, model_meta->mm_geo.lower >= MIN_PAGENO);
    mdbx_ensure(env, model_meta->mm_geo.upper <= MAX_PAGENO);
    mdbx_ensure(env, model_meta->mm_geo.now >= model_meta->mm_geo.lower);
    mdbx_ensure(env, model_meta->mm_geo.now <= model_meta->mm_geo.upper);
    mdbx_ensure(env, model_meta->mm_geo.next >= MIN_PAGENO);
    mdbx_ensure(env, model_meta->mm_geo.next <= model_meta->mm_geo.now);
    mdbx_ensure(env,
                model_meta->mm_geo.grow == bytes2pgno(env, env->me_dbgeo.grow));
    mdbx_ensure(env, model_meta->mm_geo.shrink ==
                         bytes2pgno(env, env->me_dbgeo.shrink));
  
    model_meta->mm_psize = env->me_psize;
    model_meta->mm_flags = (uint16_t)env->me_flags;
    model_meta->mm_flags |=
        MDBX_INTEGERKEY; /* this is mm_dbs[FREE_DBI].md_flags */
    model_meta->mm_dbs[FREE_DBI].md_root = P_INVALID;
    model_meta->mm_dbs[MAIN_DBI].md_root = P_INVALID;
    mdbx_meta_set_txnid(env, model_meta, MIN_TXNID + num);
    model_meta->mm_datasync_sign = mdbx_meta_sign(model_meta);
    return (MDBX_page *)((uint8_t *)model + env->me_psize);
  }
  
  /* Fill in most of the zeroed meta-pages for an empty database environment.
   * Return pointer to recently (head) meta-page. */
  static MDBX_meta *__cold mdbx_init_metas(const MDBX_env *env, void *buffer) {
    MDBX_page *page0 = (MDBX_page *)buffer;
    MDBX_page *page1 = mdbx_meta_model(env, page0, 0);
    MDBX_page *page2 = mdbx_meta_model(env, page1, 1);
    mdbx_meta_model(env, page2, 2);
    mdbx_assert(env, !mdbx_meta_eq(env, page_meta(page0), page_meta(page1)));
    mdbx_assert(env, !mdbx_meta_eq(env, page_meta(page1), page_meta(page2)));
    mdbx_assert(env, !mdbx_meta_eq(env, page_meta(page2), page_meta(page0)));
    return page_meta(page2);
  }
  
  static int mdbx_sync_locked(MDBX_env *env, unsigned flags,
                              MDBX_meta *const pending) {
    mdbx_assert(env, ((env->me_flags ^ flags) & MDBX_WRITEMAP) == 0);
    MDBX_meta *const meta0 = METAPAGE(env, 0);
    MDBX_meta *const meta1 = METAPAGE(env, 1);
    MDBX_meta *const meta2 = METAPAGE(env, 2);
    MDBX_meta *const head = mdbx_meta_head(env);
    int rc;
  
    mdbx_assert(env, mdbx_meta_eq_mask(env) == 0);
    mdbx_assert(env,
                pending < METAPAGE(env, 0) || pending > METAPAGE(env, NUM_METAS));
    mdbx_assert(env, (env->me_flags & (MDBX_RDONLY | MDBX_FATAL_ERROR)) == 0);
    mdbx_assert(env, pending->mm_geo.next <= pending->mm_geo.now);
  
    if (flags & MDBX_SAFE_NOSYNC) {
      /* Check auto-sync conditions */
      const pgno_t autosync_threshold = *env->me_autosync_threshold;
      const uint64_t autosync_period = *env->me_autosync_period;
      if ((autosync_threshold && *env->me_unsynced_pages >= autosync_threshold) ||
          (autosync_period &&
           mdbx_osal_monotime() - *env->me_sync_timestamp >= autosync_period))
        flags &= MDBX_WRITEMAP | MDBX_SHRINK_ALLOWED; /* force steady */
    }
  
    pgno_t shrink = 0;
    if (flags & MDBX_SHRINK_ALLOWED) {
      /* LY: check conditions to discard unused pages */
      const pgno_t largest_pgno = mdbx_find_largest(
          env, (head->mm_geo.next > pending->mm_geo.next) ? head->mm_geo.next
                                                          : pending->mm_geo.next);
      mdbx_assert(env, largest_pgno >= NUM_METAS);
  #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
      const pgno_t edge = env->me_poison_edge;
      if (edge > largest_pgno) {
        env->me_poison_edge = largest_pgno;
        VALGRIND_MAKE_MEM_NOACCESS(env->me_map + pgno2bytes(env, largest_pgno),
                                   pgno2bytes(env, edge - largest_pgno));
        ASAN_POISON_MEMORY_REGION(env->me_map + pgno2bytes(env, largest_pgno),
                                  pgno2bytes(env, edge - largest_pgno));
      }
  #endif /* MDBX_USE_VALGRIND || __SANITIZE_ADDRESS__ */
  #if defined(MADV_DONTNEED)
      const size_t largest_bytes = pgno2bytes(env, largest_pgno);
      /* threshold to avoid unreasonable frequent madvise() calls */
      const size_t madvise_threshold = (largest_bytes < 65536 * 256)
                                           ? 65536
                                           : (largest_bytes > MEGABYTE * 4 * 256)
                                                 ? MEGABYTE * 4
                                                 : largest_bytes >> 10;
      const size_t discard_edge_bytes = bytes_align2os_bytes(
          env, ((MDBX_RDONLY &
                 (env->me_lck ? env->me_lck->mti_envmode : env->me_flags))
                    ? largest_bytes
                    : largest_bytes + madvise_threshold));
      const pgno_t discard_edge_pgno = bytes2pgno(env, discard_edge_bytes);
      const pgno_t prev_discarded_pgno = *env->me_discarded_tail;
      if (prev_discarded_pgno >=
          discard_edge_pgno + bytes2pgno(env, madvise_threshold)) {
        mdbx_notice("open-MADV_%s %u..%u", "DONTNEED", *env->me_discarded_tail,
                    largest_pgno);
        *env->me_discarded_tail = discard_edge_pgno;
        const size_t prev_discarded_bytes =
            ceil_powerof2(pgno2bytes(env, prev_discarded_pgno), env->me_os_psize);
        mdbx_ensure(env, prev_discarded_bytes > discard_edge_bytes);
        int advise = MADV_DONTNEED;
  #if defined(MADV_FREE) &&                                                      \
      0 /* MADV_FREE works for only anonymous vma at the moment */
        if ((env->me_flags & MDBX_WRITEMAP) &&
            mdbx_linux_kernel_version > 0x04050000)
          advise = MADV_FREE;
  #endif /* MADV_FREE */
        int err = madvise(env->me_map + discard_edge_bytes,
                          prev_discarded_bytes - discard_edge_bytes, advise)
                      ? ignore_enosys(errno)
                      : MDBX_SUCCESS;
        if (unlikely(MDBX_IS_ERROR(err)))
          return err;
      }
  #endif /* MADV_FREE || MADV_DONTNEED */
  
      /* LY: check conditions to shrink datafile */
      const pgno_t backlog_gap = 3 + pending->mm_dbs[FREE_DBI].md_depth * 3;
      if (pending->mm_geo.shrink && pending->mm_geo.now - pending->mm_geo.next >
                                        pending->mm_geo.shrink + backlog_gap) {
        if (pending->mm_geo.now > largest_pgno &&
            pending->mm_geo.now - largest_pgno >
                pending->mm_geo.shrink + backlog_gap) {
          const pgno_t aligner = pending->mm_geo.grow ? pending->mm_geo.grow
                                                      : pending->mm_geo.shrink;
          const pgno_t with_backlog_gap = largest_pgno + backlog_gap;
          const pgno_t aligned = pgno_align2os_pgno(
              env, with_backlog_gap + aligner - with_backlog_gap % aligner);
          const pgno_t bottom =
              (aligned > pending->mm_geo.lower) ? aligned : pending->mm_geo.lower;
          if (pending->mm_geo.now > bottom) {
            if (META_IS_STEADY(mdbx_meta_steady(env)))
              /* force steady, but only if steady-checkpoint is present */
              flags &= MDBX_WRITEMAP | MDBX_SHRINK_ALLOWED;
            shrink = pending->mm_geo.now - bottom;
            pending->mm_geo.now = bottom;
            if (unlikely(mdbx_meta_txnid_stable(env, head) ==
                         pending->mm_txnid_a.inconsistent)) {
              const txnid_t txnid =
                  safe64_txnid_next(pending->mm_txnid_a.inconsistent);
              if (unlikely(txnid > MAX_TXNID)) {
                mdbx_error("%s", "txnid overflow!");
                rc = MDBX_TXN_FULL;
                goto fail;
              }
              mdbx_meta_set_txnid(env, pending, txnid);
            }
          }
        }
      }
    }
  
    /* LY: step#1 - sync previously written/updated data-pages */
    rc = MDBX_RESULT_FALSE /* carry steady */;
    if (*env->me_unsynced_pages) {
      mdbx_assert(env, ((flags ^ env->me_flags) & MDBX_WRITEMAP) == 0);
      enum mdbx_syncmode_bits mode_bits = MDBX_SYNC_NONE;
      if ((flags & MDBX_SAFE_NOSYNC) == 0) {
        mode_bits = MDBX_SYNC_DATA;
        if (pending->mm_geo.next > mdbx_meta_steady(env)->mm_geo.now)
          mode_bits |= MDBX_SYNC_SIZE;
        if (flags & MDBX_NOMETASYNC)
          mode_bits |= MDBX_SYNC_IODQ;
      }
      if (flags & MDBX_WRITEMAP)
        rc =
            mdbx_msync(&env->me_dxb_mmap, 0,
                       pgno_align2os_bytes(env, pending->mm_geo.next), mode_bits);
      else
        rc = mdbx_fsync(env->me_lazy_fd, mode_bits);
      if (unlikely(rc != MDBX_SUCCESS))
        goto fail;
      rc = (flags & MDBX_SAFE_NOSYNC) ? MDBX_RESULT_TRUE /* carry non-steady */
                                      : MDBX_RESULT_FALSE /* carry steady */;
    }
  
    /* Steady or Weak */
    if (rc == MDBX_RESULT_FALSE /* carry steady */) {
      pending->mm_datasync_sign = mdbx_meta_sign(pending);
      *env->me_unsynced_pages = 0;
      *env->me_sync_timestamp = mdbx_osal_monotime();
    } else {
      assert(rc == MDBX_RESULT_TRUE /* carry non-steady */);
      pending->mm_datasync_sign = MDBX_DATASIGN_WEAK;
    }
  
    MDBX_meta *target = nullptr;
    if (mdbx_meta_txnid_stable(env, head) == pending->mm_txnid_a.inconsistent) {
      mdbx_assert(env, memcmp(&head->mm_dbs, &pending->mm_dbs,
                              sizeof(head->mm_dbs)) == 0);
      mdbx_assert(env, memcmp(&head->mm_canary, &pending->mm_canary,
                              sizeof(head->mm_canary)) == 0);
      mdbx_assert(env, memcmp(&head->mm_geo, &pending->mm_geo,
                              sizeof(pending->mm_geo)) == 0);
      if (!META_IS_STEADY(head) && META_IS_STEADY(pending))
        target = head;
      else {
        mdbx_ensure(env, mdbx_meta_eq(env, head, pending));
        mdbx_debug("%s", "skip update meta");
        return MDBX_SUCCESS;
      }
    } else if (head == meta0)
      target = mdbx_meta_ancient(prefer_steady, env, meta1, meta2);
    else if (head == meta1)
      target = mdbx_meta_ancient(prefer_steady, env, meta0, meta2);
    else {
      mdbx_assert(env, head == meta2);
      target = mdbx_meta_ancient(prefer_steady, env, meta0, meta1);
    }
  
    /* LY: step#2 - update meta-page. */
    mdbx_debug("writing meta%" PRIaPGNO " = root %" PRIaPGNO "/%" PRIaPGNO
               ", geo %" PRIaPGNO "/%" PRIaPGNO "-%" PRIaPGNO "/%" PRIaPGNO
               " +%u -%u, txn_id %" PRIaTXN ", %s",
               data_page(target)->mp_pgno, pending->mm_dbs[MAIN_DBI].md_root,
               pending->mm_dbs[FREE_DBI].md_root, pending->mm_geo.lower,
               pending->mm_geo.next, pending->mm_geo.now, pending->mm_geo.upper,
               pending->mm_geo.grow, pending->mm_geo.shrink,
               pending->mm_txnid_a.inconsistent, mdbx_durable_str(pending));
  
    mdbx_debug("meta0: %s, %s, txn_id %" PRIaTXN ", root %" PRIaPGNO
               "/%" PRIaPGNO,
               (meta0 == head) ? "head" : (meta0 == target) ? "tail" : "stay",
               mdbx_durable_str(meta0), mdbx_meta_txnid_fluid(env, meta0),
               meta0->mm_dbs[MAIN_DBI].md_root, meta0->mm_dbs[FREE_DBI].md_root);
    mdbx_debug("meta1: %s, %s, txn_id %" PRIaTXN ", root %" PRIaPGNO
               "/%" PRIaPGNO,
               (meta1 == head) ? "head" : (meta1 == target) ? "tail" : "stay",
               mdbx_durable_str(meta1), mdbx_meta_txnid_fluid(env, meta1),
               meta1->mm_dbs[MAIN_DBI].md_root, meta1->mm_dbs[FREE_DBI].md_root);
    mdbx_debug("meta2: %s, %s, txn_id %" PRIaTXN ", root %" PRIaPGNO
               "/%" PRIaPGNO,
               (meta2 == head) ? "head" : (meta2 == target) ? "tail" : "stay",
               mdbx_durable_str(meta2), mdbx_meta_txnid_fluid(env, meta2),
               meta2->mm_dbs[MAIN_DBI].md_root, meta2->mm_dbs[FREE_DBI].md_root);
  
    mdbx_assert(env, !mdbx_meta_eq(env, pending, meta0));
    mdbx_assert(env, !mdbx_meta_eq(env, pending, meta1));
    mdbx_assert(env, !mdbx_meta_eq(env, pending, meta2));
  
    mdbx_assert(env, ((env->me_flags ^ flags) & MDBX_WRITEMAP) == 0);
    mdbx_ensure(env, target == head || mdbx_meta_txnid_stable(env, target) <
                                           pending->mm_txnid_a.inconsistent);
    if (flags & MDBX_WRITEMAP) {
      mdbx_jitter4testing(true);
      if (likely(target != head)) {
        /* LY: 'invalidate' the meta. */
        mdbx_meta_update_begin(env, target, pending->mm_txnid_a.inconsistent);
        target->mm_datasync_sign = MDBX_DATASIGN_WEAK;
  #ifndef NDEBUG
        /* debug: provoke failure to catch a violators, but don't touch mm_psize
         * and mm_flags to allow readers catch actual pagesize. */
        uint8_t *provoke_begin = (uint8_t *)&target->mm_dbs[FREE_DBI].md_root;
        uint8_t *provoke_end = (uint8_t *)&target->mm_datasync_sign;
        memset(provoke_begin, 0xCC, provoke_end - provoke_begin);
        mdbx_jitter4testing(false);
  #endif
  
        /* LY: update info */
        target->mm_geo = pending->mm_geo;
        target->mm_dbs[FREE_DBI] = pending->mm_dbs[FREE_DBI];
        target->mm_dbs[MAIN_DBI] = pending->mm_dbs[MAIN_DBI];
        target->mm_canary = pending->mm_canary;
        target->mm_pages_retired = pending->mm_pages_retired;
        mdbx_jitter4testing(true);
        mdbx_flush_incoherent_cpu_writeback();
  
        /* LY: 'commit' the meta */
        mdbx_meta_update_end(env, target, pending->mm_txnid_b.inconsistent);
        mdbx_jitter4testing(true);
      } else {
        /* dangerous case (target == head), only mm_datasync_sign could
         * me updated, check assertions once again */
        mdbx_ensure(env, mdbx_meta_txnid_stable(env, head) ==
                                 pending->mm_txnid_a.inconsistent &&
                             !META_IS_STEADY(head) && META_IS_STEADY(pending));
        mdbx_ensure(env, memcmp(&head->mm_geo, &pending->mm_geo,
                                sizeof(head->mm_geo)) == 0);
        mdbx_ensure(env, memcmp(&head->mm_dbs, &pending->mm_dbs,
                                sizeof(head->mm_dbs)) == 0);
        mdbx_ensure(env, memcmp(&head->mm_canary, &pending->mm_canary,
                                sizeof(head->mm_canary)) == 0);
      }
      target->mm_datasync_sign = pending->mm_datasync_sign;
      mdbx_flush_incoherent_cpu_writeback();
      mdbx_jitter4testing(true);
      /* sync meta-pages */
      rc =
          mdbx_msync(&env->me_dxb_mmap, 0, pgno_align2os_bytes(env, NUM_METAS),
                     (flags & MDBX_NOMETASYNC) ? MDBX_SYNC_NONE
                                               : MDBX_SYNC_DATA | MDBX_SYNC_IODQ);
      if (unlikely(rc != MDBX_SUCCESS))
        goto fail;
    } else {
      const MDBX_meta undo_meta = *target;
      const mdbx_filehandle_t fd = (env->me_dsync_fd != INVALID_HANDLE_VALUE)
                                       ? env->me_dsync_fd
                                       : env->me_lazy_fd;
      rc = mdbx_pwrite(fd, pending, sizeof(MDBX_meta),
                       (uint8_t *)target - env->me_map);
      if (unlikely(rc != MDBX_SUCCESS)) {
      undo:
        mdbx_debug("%s", "write failed, disk error?");
        /* On a failure, the pagecache still contains the new data.
         * Try write some old data back, to prevent it from being used. */
        mdbx_pwrite(fd, &undo_meta, sizeof(MDBX_meta),
                    (uint8_t *)target - env->me_map);
        goto fail;
      }
      mdbx_flush_incoherent_mmap(target, sizeof(MDBX_meta), env->me_os_psize);
      /* sync meta-pages */
      if ((flags & MDBX_NOMETASYNC) == 0 && fd == env->me_lazy_fd) {
        rc = mdbx_fsync(env->me_lazy_fd, MDBX_SYNC_DATA | MDBX_SYNC_IODQ);
        if (rc != MDBX_SUCCESS)
          goto undo;
      }
    }
    if (flags & MDBX_NOMETASYNC)
      *env->me_unsynced_pages += 1;
    else
      *env->me_meta_sync_txnid = pending->mm_txnid_a.low;
  
    /* LY: shrink datafile if needed */
    if (unlikely(shrink)) {
      mdbx_verbose("shrink to %" PRIaPGNO " pages (-%" PRIaPGNO ")",
                   pending->mm_geo.now, shrink);
      rc = mdbx_mapresize_implicit(env, pending->mm_geo.next, pending->mm_geo.now,
                                   pending->mm_geo.upper);
      if (MDBX_IS_ERROR(rc))
        goto fail;
    }
  
    if (likely(env->me_lck))
      /* toggle oldest refresh */
      env->me_lck->mti_readers_refresh_flag = false;
  
    return MDBX_SUCCESS;
  
  fail:
    env->me_flags |= MDBX_FATAL_ERROR;
    return rc;
  }
  
  static void __cold mdbx_setup_pagesize(MDBX_env *env, const size_t pagesize) {
    STATIC_ASSERT(PTRDIFF_MAX > MAX_MAPSIZE);
    STATIC_ASSERT(MIN_PAGESIZE > sizeof(MDBX_page) + sizeof(MDBX_meta));
    mdbx_ensure(env, is_powerof2(pagesize));
    mdbx_ensure(env, pagesize >= MIN_PAGESIZE);
    mdbx_ensure(env, pagesize <= MAX_PAGESIZE);
    env->me_psize = (unsigned)pagesize;
  
    STATIC_ASSERT(MAX_GC1OVPAGE(MIN_PAGESIZE) > 4);
    STATIC_ASSERT(MAX_GC1OVPAGE(MAX_PAGESIZE) < MDBX_DPL_TXNFULL);
    const intptr_t maxgc_ov1page = (pagesize - PAGEHDRSZ) / sizeof(pgno_t) - 1;
    mdbx_ensure(env,
                maxgc_ov1page > 42 && maxgc_ov1page < (intptr_t)MDBX_DPL_TXNFULL);
    env->me_maxgc_ov1page = (unsigned)maxgc_ov1page;
  
    STATIC_ASSERT(LEAF_NODEMAX(MIN_PAGESIZE) > sizeof(MDBX_db) + NODESIZE + 42);
    STATIC_ASSERT(LEAF_NODEMAX(MAX_PAGESIZE) < UINT16_MAX);
    STATIC_ASSERT(LEAF_NODEMAX(MIN_PAGESIZE) > BRANCH_NODEMAX(MIN_PAGESIZE));
    STATIC_ASSERT(BRANCH_NODEMAX(MAX_PAGESIZE) > NODESIZE + 42);
    STATIC_ASSERT(BRANCH_NODEMAX(MAX_PAGESIZE) < UINT16_MAX);
    const intptr_t branch_nodemax = BRANCH_NODEMAX(pagesize);
    mdbx_ensure(env, branch_nodemax > 42 && branch_nodemax < (int)UINT16_MAX &&
                         branch_nodemax % 2 == 0);
    env->me_branch_nodemax = (unsigned)branch_nodemax;
    env->me_psize2log = (uint8_t)log2n(pagesize);
    mdbx_assert(env, pgno2bytes(env, 1) == pagesize);
    mdbx_assert(env, bytes2pgno(env, pagesize + pagesize) == 2);
  }
  
  __cold int mdbx_env_create(MDBX_env **penv) {
    MDBX_env *env = mdbx_calloc(1, sizeof(MDBX_env));
    if (unlikely(!env))
      return MDBX_ENOMEM;
  
    env->me_maxreaders = DEFAULT_READERS;
    env->me_maxdbs = env->me_numdbs = CORE_DBS;
    env->me_lazy_fd = INVALID_HANDLE_VALUE;
    env->me_dsync_fd = INVALID_HANDLE_VALUE;
    env->me_lfd = INVALID_HANDLE_VALUE;
    env->me_pid = mdbx_getpid();
    env->me_stuck_meta = -1;
  
    int rc;
    const size_t os_psize = mdbx_syspagesize();
    if (unlikely(!is_powerof2(os_psize) || os_psize < MIN_PAGESIZE)) {
      mdbx_error("unsuitable system pagesize %" PRIuPTR, os_psize);
      rc = MDBX_INCOMPATIBLE;
      goto bailout;
    }
    env->me_os_psize = (unsigned)os_psize;
    mdbx_setup_pagesize(env, env->me_os_psize);
  
    rc = mdbx_fastmutex_init(&env->me_dbi_lock);
    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout;
  
  #if defined(_WIN32) || defined(_WIN64)
    mdbx_srwlock_Init(&env->me_remap_guard);
    InitializeCriticalSection(&env->me_windowsbug_lock);
  #else
    rc = mdbx_fastmutex_init(&env->me_remap_guard);
    if (unlikely(rc != MDBX_SUCCESS)) {
      mdbx_fastmutex_destroy(&env->me_dbi_lock);
      goto bailout;
    }
  
  #if MDBX_LOCKING > MDBX_LOCKING_SYSV
    rc = mdbx_ipclock_stub(&env->me_lckless_stub.wlock);
  #endif /* MDBX_LOCKING */
    if (unlikely(rc != MDBX_SUCCESS)) {
      mdbx_fastmutex_destroy(&env->me_remap_guard);
      mdbx_fastmutex_destroy(&env->me_dbi_lock);
      goto bailout;
    }
  #endif /* Windows */
  
    VALGRIND_CREATE_MEMPOOL(env, 0, 0);
    env->me_signature = MDBX_ME_SIGNATURE;
    *penv = env;
    return MDBX_SUCCESS;
  
  bailout:
    mdbx_free(env);
    *penv = nullptr;
    return rc;
  }
  
  __cold LIBMDBX_API int
  mdbx_env_set_geometry(MDBX_env *env, intptr_t size_lower, intptr_t size_now,
                        intptr_t size_upper, intptr_t growth_step,
                        intptr_t shrink_threshold, intptr_t pagesize) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    const bool inside_txn =
        (env->me_txn0 && env->me_txn0->mt_owner == mdbx_thread_self());
  
  #if MDBX_DEBUG
    if (growth_step < 0)
      growth_step = 1;
    if (shrink_threshold < 0)
      shrink_threshold = 1;
  #endif
  
    bool need_unlock = false;
    rc = MDBX_PROBLEM;
    if (env->me_map) {
      /* env already mapped */
      if (unlikely(env->me_flags & MDBX_RDONLY))
        return MDBX_EACCESS;
  
      if (!inside_txn) {
        int err = mdbx_txn_lock(env, false);
        if (unlikely(err != MDBX_SUCCESS))
          return err;
        need_unlock = true;
      }
      MDBX_meta *head = mdbx_meta_head(env);
      if (!inside_txn) {
        env->me_txn0->mt_txnid = meta_txnid(env, head, false);
        mdbx_find_oldest(env->me_txn0);
      }
  
      /* get untouched params from DB */
      if (pagesize <= 0 || pagesize >= INT_MAX)
        pagesize = env->me_psize;
      if (size_lower < 0)
        size_lower = pgno2bytes(env, head->mm_geo.lower);
      if (size_now < 0)
        size_now = pgno2bytes(env, head->mm_geo.now);
      if (size_upper < 0)
        size_upper = pgno2bytes(env, head->mm_geo.upper);
      if (growth_step < 0)
        growth_step = pgno2bytes(env, head->mm_geo.grow);
      if (shrink_threshold < 0)
        shrink_threshold = pgno2bytes(env, head->mm_geo.shrink);
  
      if (pagesize != (intptr_t)env->me_psize) {
        rc = MDBX_EINVAL;
        goto bailout;
      }
      const size_t usedbytes =
          pgno2bytes(env, mdbx_find_largest(env, head->mm_geo.next));
      if ((size_t)size_upper < usedbytes) {
        rc = MDBX_MAP_FULL;
        goto bailout;
      }
      if ((size_t)size_now < usedbytes)
        size_now = usedbytes;
    } else {
      /* env NOT yet mapped */
      if (unlikely(inside_txn))
        return MDBX_PANIC;
  
      /* is requested some auto-value for pagesize ? */
      if (pagesize >= INT_MAX /* maximal */)
        pagesize = MAX_PAGESIZE;
      else if (pagesize <= 0) {
        if (pagesize < 0 /* default */) {
          pagesize = env->me_os_psize;
          if ((uintptr_t)pagesize > MAX_PAGESIZE)
            pagesize = MAX_PAGESIZE;
          mdbx_assert(env, (uintptr_t)pagesize >= MIN_PAGESIZE);
        } else if (pagesize == 0 /* minimal */)
          pagesize = MIN_PAGESIZE;
  
        /* choose pagesize */
        intptr_t max_size = (size_now > size_lower) ? size_now : size_lower;
        max_size = (size_upper > max_size) ? size_upper : max_size;
        if (max_size < 0 /* default */)
          max_size = DEFAULT_MAPSIZE;
        else if (max_size == 0 /* minimal */)
          max_size = MIN_MAPSIZE;
        else if (max_size >= (intptr_t)MAX_MAPSIZE /* maximal */)
          max_size = MAX_MAPSIZE;
  
        while (max_size > pagesize * (int64_t)MAX_PAGENO &&
               pagesize < MAX_PAGESIZE)
          pagesize <<= 1;
      }
    }
  
    if (pagesize < (intptr_t)MIN_PAGESIZE || pagesize > (intptr_t)MAX_PAGESIZE ||
        !is_powerof2(pagesize)) {
      rc = MDBX_EINVAL;
      goto bailout;
    }
  
    if (size_lower <= 0) {
      size_lower = MIN_MAPSIZE;
      if (MIN_MAPSIZE / pagesize < MIN_PAGENO)
        size_lower = MIN_PAGENO * pagesize;
    }
    if (size_lower == INTPTR_MAX)
      size_lower = MAX_MAPSIZE;
  
    if (size_now <= 0) {
      size_now = DEFAULT_MAPSIZE;
      if (size_now < size_lower)
        size_now = size_lower;
      if (size_upper >= size_lower && size_now > size_upper)
        size_now = size_upper;
    }
    if (size_now == INTPTR_MAX)
      size_now = MAX_MAPSIZE;
  
    if (size_upper <= 0) {
      if ((size_t)size_now >= MAX_MAPSIZE / 2)
        size_upper = MAX_MAPSIZE;
      else if (MAX_MAPSIZE != MAX_MAPSIZE32 &&
               (size_t)size_now >= MAX_MAPSIZE32 / 2 &&
               (size_t)size_now <= MAX_MAPSIZE32 / 4 * 3)
        size_upper = MAX_MAPSIZE32;
      else {
        size_upper = size_now + size_now;
        if ((size_t)size_upper < DEFAULT_MAPSIZE * 2)
          size_upper = DEFAULT_MAPSIZE * 2;
      }
      if ((size_t)size_upper / pagesize > MAX_PAGENO)
        size_upper = pagesize * MAX_PAGENO;
    }
  
    if (unlikely(size_lower < (intptr_t)MIN_MAPSIZE || size_lower > size_upper)) {
      rc = MDBX_EINVAL;
      goto bailout;
    }
  
    if ((uint64_t)size_lower / pagesize < MIN_PAGENO) {
      rc = MDBX_EINVAL;
      goto bailout;
    }
  
    if (unlikely((size_t)size_upper > MAX_MAPSIZE ||
                 (uint64_t)size_upper / pagesize > MAX_PAGENO)) {
      rc = MDBX_TOO_LARGE;
      goto bailout;
    }
  
    const size_t unit = (env->me_os_psize > (size_t)pagesize) ? env->me_os_psize
                                                              : (size_t)pagesize;
    size_lower = ceil_powerof2(size_lower, unit);
    size_upper = ceil_powerof2(size_upper, unit);
    size_now = ceil_powerof2(size_now, unit);
  
    /* LY: подбираем значение size_upper:
     *  - кратное размеру страницы
     *  - без нарушения MAX_MAPSIZE и MAX_PAGENO */
    while (unlikely((size_t)size_upper > MAX_MAPSIZE ||
                    (uint64_t)size_upper / pagesize > MAX_PAGENO)) {
      if ((size_t)size_upper < unit + MIN_MAPSIZE ||
          (size_t)size_upper < (size_t)pagesize * (MIN_PAGENO + 1)) {
        /* паранойа на случай переполнения при невероятных значениях */
        rc = MDBX_EINVAL;
        goto bailout;
      }
      size_upper -= unit;
      if ((size_t)size_upper < (size_t)size_lower)
        size_lower = size_upper;
    }
    mdbx_assert(env, (size_upper - size_lower) % env->me_os_psize == 0);
  
    if (size_now < size_lower)
      size_now = size_lower;
    if (size_now > size_upper)
      size_now = size_upper;
  
    if (growth_step < 0) {
      growth_step = ((size_t)(size_upper - size_lower)) / 42;
      if (growth_step > size_lower)
        growth_step = size_lower;
      if (growth_step < 65536)
        growth_step = 65536;
      if ((size_t)growth_step > MEGABYTE * 16)
        growth_step = MEGABYTE * 16;
    }
    if (growth_step == 0 && shrink_threshold > 0)
      growth_step = 1;
    growth_step = ceil_powerof2(growth_step, unit);
    if (bytes2pgno(env, growth_step) > UINT16_MAX)
      growth_step = pgno2bytes(env, UINT16_MAX);
  
    if (shrink_threshold < 0)
      shrink_threshold = growth_step + growth_step;
    shrink_threshold = ceil_powerof2(shrink_threshold, unit);
    if (bytes2pgno(env, shrink_threshold) > UINT16_MAX)
      shrink_threshold = pgno2bytes(env, UINT16_MAX);
  
    /* save user's geo-params for future open/create */
    env->me_dbgeo.lower = size_lower;
    env->me_dbgeo.now = size_now;
    env->me_dbgeo.upper = size_upper;
    env->me_dbgeo.grow = growth_step;
    env->me_dbgeo.shrink = shrink_threshold;
    rc = MDBX_SUCCESS;
  
    mdbx_ensure(env, pagesize >= MIN_PAGESIZE);
    mdbx_ensure(env, pagesize <= MAX_PAGESIZE);
    mdbx_ensure(env, is_powerof2(pagesize));
    mdbx_ensure(env, is_powerof2(env->me_os_psize));
  
    mdbx_ensure(env, env->me_dbgeo.lower >= MIN_MAPSIZE);
    mdbx_ensure(env, env->me_dbgeo.lower / pagesize >= MIN_PAGENO);
    mdbx_ensure(env, env->me_dbgeo.lower % pagesize == 0);
    mdbx_ensure(env, env->me_dbgeo.lower % env->me_os_psize == 0);
  
    mdbx_ensure(env, env->me_dbgeo.upper <= MAX_MAPSIZE);
    mdbx_ensure(env, env->me_dbgeo.upper / pagesize <= MAX_PAGENO);
    mdbx_ensure(env, env->me_dbgeo.upper % pagesize == 0);
    mdbx_ensure(env, env->me_dbgeo.upper % env->me_os_psize == 0);
  
    mdbx_ensure(env, env->me_dbgeo.now >= env->me_dbgeo.lower);
    mdbx_ensure(env, env->me_dbgeo.now <= env->me_dbgeo.upper);
    mdbx_ensure(env, env->me_dbgeo.now % pagesize == 0);
    mdbx_ensure(env, env->me_dbgeo.now % env->me_os_psize == 0);
  
    mdbx_ensure(env, env->me_dbgeo.grow % pagesize == 0);
    mdbx_ensure(env, env->me_dbgeo.grow % env->me_os_psize == 0);
    mdbx_ensure(env, env->me_dbgeo.shrink % pagesize == 0);
    mdbx_ensure(env, env->me_dbgeo.shrink % env->me_os_psize == 0);
  
    if (env->me_map) {
      /* apply new params to opened environment */
      mdbx_ensure(env, pagesize == (intptr_t)env->me_psize);
      MDBX_meta meta;
      MDBX_meta *head = nullptr;
      const mdbx_geo_t *current_geo;
      if (inside_txn) {
        current_geo = &env->me_txn->mt_geo;
      } else {
        head = mdbx_meta_head(env);
        meta = *head;
        current_geo = &meta.mm_geo;
      }
  
      mdbx_geo_t new_geo;
      new_geo.lower = bytes2pgno(env, env->me_dbgeo.lower);
      new_geo.now = bytes2pgno(env, env->me_dbgeo.now);
      new_geo.upper = bytes2pgno(env, env->me_dbgeo.upper);
      new_geo.grow = (uint16_t)bytes2pgno(env, env->me_dbgeo.grow);
      new_geo.shrink = (uint16_t)bytes2pgno(env, env->me_dbgeo.shrink);
      new_geo.next = current_geo->next;
  
      mdbx_ensure(env,
                  pgno_align2os_bytes(env, new_geo.lower) == env->me_dbgeo.lower);
      mdbx_ensure(env,
                  pgno_align2os_bytes(env, new_geo.upper) == env->me_dbgeo.upper);
      mdbx_ensure(env,
                  pgno_align2os_bytes(env, new_geo.now) == env->me_dbgeo.now);
      mdbx_ensure(env,
                  pgno_align2os_bytes(env, new_geo.grow) == env->me_dbgeo.grow);
      mdbx_ensure(env, pgno_align2os_bytes(env, new_geo.shrink) ==
                           env->me_dbgeo.shrink);
  
      mdbx_ensure(env, env->me_dbgeo.lower >= MIN_MAPSIZE);
      mdbx_ensure(env, new_geo.lower >= MIN_PAGENO);
      mdbx_ensure(env, env->me_dbgeo.upper <= MAX_MAPSIZE);
      mdbx_ensure(env, new_geo.upper <= MAX_PAGENO);
      mdbx_ensure(env, new_geo.now >= new_geo.next);
      mdbx_ensure(env, new_geo.upper >= new_geo.now);
      mdbx_ensure(env, new_geo.now >= new_geo.lower);
  
      if (memcmp(current_geo, &new_geo, sizeof(mdbx_geo_t)) != 0) {
  #if defined(_WIN32) || defined(_WIN64)
        /* Was DB shrinking disabled before and now it will be enabled? */
        if (new_geo.lower < new_geo.upper && new_geo.shrink &&
            !(current_geo->lower < current_geo->upper && current_geo->shrink)) {
          if (!env->me_lck) {
            rc = MDBX_EPERM;
            goto bailout;
          }
          int err = mdbx_rdt_lock(env);
          if (unlikely(MDBX_IS_ERROR(err))) {
            rc = err;
            goto bailout;
          }
  
          /* Check if there are any reading threads that do not use the SRWL */
          const size_t CurrentTid = GetCurrentThreadId();
          const MDBX_reader *const begin = env->me_lck->mti_readers;
          const MDBX_reader *const end = begin + env->me_lck->mti_numreaders;
          for (const MDBX_reader *reader = begin; reader < end; ++reader) {
            if (reader->mr_pid == env->me_pid && reader->mr_tid &&
                reader->mr_tid != CurrentTid) {
              /* At least one thread may don't use SRWL */
              rc = MDBX_EPERM;
              break;
            }
          }
  
          mdbx_rdt_unlock(env);
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
        }
  #endif
  
        if (new_geo.now != current_geo->now ||
            new_geo.upper != current_geo->upper) {
          rc = mdbx_mapresize(env, current_geo->next, new_geo.now, new_geo.upper,
                              false);
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
          mdbx_assert(env, (head == nullptr) == inside_txn);
          if (head)
            head = /* base address could be changed */ mdbx_meta_head(env);
        }
        if (inside_txn) {
          env->me_txn->mt_geo = new_geo;
          env->me_txn->mt_flags |= MDBX_TXN_DIRTY;
        } else {
          meta.mm_geo = new_geo;
          const txnid_t txnid =
              safe64_txnid_next(mdbx_meta_txnid_stable(env, head));
          if (unlikely(txnid > MAX_TXNID)) {
            mdbx_error("%s", "txnid overflow!");
            rc = MDBX_TXN_FULL;
            goto bailout;
          }
          mdbx_meta_set_txnid(env, &meta, txnid);
          rc = mdbx_sync_locked(env, env->me_flags, &meta);
        }
      }
    } else if (pagesize != (intptr_t)env->me_psize) {
      mdbx_setup_pagesize(env, pagesize);
    }
  
  bailout:
    if (need_unlock)
      mdbx_txn_unlock(env);
    return rc;
  }
  
  __cold int mdbx_env_set_mapsize(MDBX_env *env, size_t size) {
    return __inline_mdbx_env_set_mapsize(env, size);
  }
  
  __cold int mdbx_env_set_maxdbs(MDBX_env *env, MDBX_dbi dbs) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(dbs > MDBX_MAX_DBI))
      return MDBX_EINVAL;
  
    if (unlikely(env->me_map))
      return MDBX_EPERM;
  
    env->me_maxdbs = dbs + CORE_DBS;
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_env_get_maxdbs(MDBX_env *env, MDBX_dbi *dbs) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!dbs))
      return MDBX_EINVAL;
  
    *dbs = env->me_maxdbs;
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_env_set_maxreaders(MDBX_env *env, unsigned readers) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(readers < 1 || readers > MDBX_READERS_LIMIT))
      return MDBX_EINVAL;
  
    if (unlikely(env->me_map))
      return MDBX_EPERM;
  
    env->me_maxreaders = readers;
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_env_get_maxreaders(const MDBX_env *env, unsigned *readers) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!readers))
      return MDBX_EINVAL;
  
    *readers = env->me_maxreaders;
    return MDBX_SUCCESS;
  }
  
  /* Further setup required for opening an MDBX environment */
  static __cold int mdbx_setup_dxb(MDBX_env *env, const int lck_rc) {
    uint64_t filesize_before;
    MDBX_meta meta;
    int rc = MDBX_RESULT_FALSE;
    int err = mdbx_read_header(env, &meta, &filesize_before, lck_rc);
    if (unlikely(err != MDBX_SUCCESS)) {
      if (lck_rc != /* lck exclusive */ MDBX_RESULT_TRUE || err != MDBX_ENODATA ||
          (env->me_flags & MDBX_RDONLY) != 0 ||
          /* recovery mode */ env->me_stuck_meta >= 0)
        return err;
  
      mdbx_debug("%s", "create new database");
      rc = /* new database */ MDBX_RESULT_TRUE;
  
      if (!env->me_dbgeo.now) {
        /* set defaults if not configured */
        err = mdbx_env_set_geometry(env, 0, -1, DEFAULT_MAPSIZE, -1, -1, -1);
        if (unlikely(err != MDBX_SUCCESS))
          return err;
      }
  
      void *buffer = mdbx_calloc(NUM_METAS, env->me_psize);
      if (!buffer)
        return MDBX_ENOMEM;
  
      meta = *mdbx_init_metas(env, buffer);
      err = mdbx_pwrite(env->me_lazy_fd, buffer, env->me_psize * NUM_METAS, 0);
      mdbx_free(buffer);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
  
      err = mdbx_ftruncate(env->me_lazy_fd, filesize_before = env->me_dbgeo.now);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
  
  #ifndef NDEBUG /* just for checking */
      err = mdbx_read_header(env, &meta, &filesize_before, lck_rc);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
  #endif
    }
  
    mdbx_verbose("header: root %" PRIaPGNO "/%" PRIaPGNO ", geo %" PRIaPGNO
                 "/%" PRIaPGNO "-%" PRIaPGNO "/%" PRIaPGNO
                 " +%u -%u, txn_id %" PRIaTXN ", %s",
                 meta.mm_dbs[MAIN_DBI].md_root, meta.mm_dbs[FREE_DBI].md_root,
                 meta.mm_geo.lower, meta.mm_geo.next, meta.mm_geo.now,
                 meta.mm_geo.upper, meta.mm_geo.grow, meta.mm_geo.shrink,
                 meta.mm_txnid_a.inconsistent, mdbx_durable_str(&meta));
  
    mdbx_setup_pagesize(env, meta.mm_psize);
    const size_t used_bytes = pgno2bytes(env, meta.mm_geo.next);
    const size_t used_aligned2os_bytes =
        ceil_powerof2(used_bytes, env->me_os_psize);
    if ((env->me_flags & MDBX_RDONLY) /* readonly */
        || lck_rc != MDBX_RESULT_TRUE /* not exclusive */
        || /* recovery mode */ env->me_stuck_meta >= 0) {
      /* use present params from db */
      const size_t pagesize = meta.mm_psize;
      err = mdbx_env_set_geometry(
          env, meta.mm_geo.lower * pagesize, meta.mm_geo.now * pagesize,
          meta.mm_geo.upper * pagesize, meta.mm_geo.grow * pagesize,
          meta.mm_geo.shrink * pagesize, meta.mm_psize);
      if (unlikely(err != MDBX_SUCCESS)) {
        mdbx_error("%s: err %d", "could not apply preconfigured geometry from db",
                   err);
        return (err == MDBX_EINVAL) ? MDBX_INCOMPATIBLE : err;
      }
    } else if (env->me_dbgeo.now) {
      /* silently growth to last used page */
      if (env->me_dbgeo.now < used_aligned2os_bytes)
        env->me_dbgeo.now = used_aligned2os_bytes;
      if (env->me_dbgeo.upper < used_aligned2os_bytes)
        env->me_dbgeo.upper = used_aligned2os_bytes;
  
      /* apply preconfigured params, but only if substantial changes:
       *  - upper or lower limit changes
       *  - shrink threshold or growth step
       * But ignore change just a 'now/current' size. */
      if (bytes_align2os_bytes(env, env->me_dbgeo.upper) !=
              pgno2bytes(env, meta.mm_geo.upper) ||
          bytes_align2os_bytes(env, env->me_dbgeo.lower) !=
              pgno2bytes(env, meta.mm_geo.lower) ||
          bytes_align2os_bytes(env, env->me_dbgeo.shrink) !=
              pgno2bytes(env, meta.mm_geo.shrink) ||
          bytes_align2os_bytes(env, env->me_dbgeo.grow) !=
              pgno2bytes(env, meta.mm_geo.grow)) {
  
        if (env->me_dbgeo.shrink && env->me_dbgeo.now > used_bytes)
          /* pre-shrink if enabled */
          env->me_dbgeo.now = used_bytes + env->me_dbgeo.shrink -
                              used_bytes % env->me_dbgeo.shrink;
  
        err = mdbx_env_set_geometry(env, env->me_dbgeo.lower, env->me_dbgeo.now,
                                    env->me_dbgeo.upper, env->me_dbgeo.grow,
                                    env->me_dbgeo.shrink, meta.mm_psize);
        if (unlikely(err != MDBX_SUCCESS)) {
          mdbx_error("%s: err %d", "could not apply preconfigured db-geometry",
                     err);
          return (err == MDBX_EINVAL) ? MDBX_INCOMPATIBLE : err;
        }
  
        /* update meta fields */
        meta.mm_geo.now = bytes2pgno(env, env->me_dbgeo.now);
        meta.mm_geo.lower = bytes2pgno(env, env->me_dbgeo.lower);
        meta.mm_geo.upper = bytes2pgno(env, env->me_dbgeo.upper);
        meta.mm_geo.grow = (uint16_t)bytes2pgno(env, env->me_dbgeo.grow);
        meta.mm_geo.shrink = (uint16_t)bytes2pgno(env, env->me_dbgeo.shrink);
  
        mdbx_verbose("amended: root %" PRIaPGNO "/%" PRIaPGNO ", geo %" PRIaPGNO
                     "/%" PRIaPGNO "-%" PRIaPGNO "/%" PRIaPGNO
                     " +%u -%u, txn_id %" PRIaTXN ", %s",
                     meta.mm_dbs[MAIN_DBI].md_root, meta.mm_dbs[FREE_DBI].md_root,
                     meta.mm_geo.lower, meta.mm_geo.next, meta.mm_geo.now,
                     meta.mm_geo.upper, meta.mm_geo.grow, meta.mm_geo.shrink,
                     meta.mm_txnid_a.inconsistent, mdbx_durable_str(&meta));
      } else {
        /* fetch back 'now/current' size, since it was ignored during comparison
         * and may differ. */
        env->me_dbgeo.now = pgno_align2os_bytes(env, meta.mm_geo.now);
      }
      mdbx_ensure(env, meta.mm_geo.now >= meta.mm_geo.next);
    } else {
      /* geo-params are not pre-configured by user,
       * get current values from the meta. */
      env->me_dbgeo.now = pgno2bytes(env, meta.mm_geo.now);
      env->me_dbgeo.lower = pgno2bytes(env, meta.mm_geo.lower);
      env->me_dbgeo.upper = pgno2bytes(env, meta.mm_geo.upper);
      env->me_dbgeo.grow = pgno2bytes(env, meta.mm_geo.grow);
      env->me_dbgeo.shrink = pgno2bytes(env, meta.mm_geo.shrink);
    }
  
    mdbx_ensure(env,
                pgno_align2os_bytes(env, meta.mm_geo.now) == env->me_dbgeo.now);
    mdbx_ensure(env, env->me_dbgeo.now >= used_bytes);
    if (unlikely(filesize_before != env->me_dbgeo.now)) {
      if (lck_rc != /* lck exclusive */ MDBX_RESULT_TRUE) {
        mdbx_verbose("filesize mismatch (expect %" PRIuPTR "b/%" PRIaPGNO
                     "p, have %" PRIu64 "b/%" PRIaPGNO "p), "
                     "assume other process working",
                     env->me_dbgeo.now, bytes2pgno(env, env->me_dbgeo.now),
                     filesize_before, bytes2pgno(env, (size_t)filesize_before));
      } else {
        mdbx_warning("filesize mismatch (expect %" PRIuSIZE "b/%" PRIaPGNO
                     "p, have %" PRIu64 "b/%" PRIaPGNO "p)",
                     env->me_dbgeo.now, bytes2pgno(env, env->me_dbgeo.now),
                     filesize_before, bytes2pgno(env, (size_t)filesize_before));
        if (filesize_before < used_bytes) {
          mdbx_error("last-page beyond end-of-file (last %" PRIaPGNO
                     ", have %" PRIaPGNO ")",
                     meta.mm_geo.next, bytes2pgno(env, (size_t)filesize_before));
          return MDBX_CORRUPTED;
        }
  
        if (env->me_flags & MDBX_RDONLY) {
          if (filesize_before & (env->me_os_psize - 1)) {
            mdbx_error("%s", "filesize should be rounded-up to system page");
            return MDBX_WANNA_RECOVERY;
          }
          mdbx_warning("%s", "ignore filesize mismatch in readonly-mode");
        } else {
          mdbx_verbose("will resize datafile to %" PRIuSIZE " bytes, %" PRIaPGNO
                       " pages",
                       env->me_dbgeo.now, bytes2pgno(env, env->me_dbgeo.now));
        }
      }
    }
  
    mdbx_verbose("current boot-id %" PRIx64 "-%" PRIx64 " (%savailable)",
                 bootid.x, bootid.y, (bootid.x | bootid.y) ? "" : "not-");
  
    /* calculate readahead hint before mmap with zero redundant pages */
    const bool readahead =
        (env->me_flags & MDBX_NORDAHEAD) == 0 &&
        mdbx_is_readahead_reasonable(used_bytes, 0) == MDBX_RESULT_TRUE;
    err = mdbx_mmap(env->me_flags, &env->me_dxb_mmap, env->me_dbgeo.now,
                    env->me_dbgeo.upper, lck_rc ? MMAP_OPTION_TRUNCATE : 0);
    if (unlikely(err != MDBX_SUCCESS))
      return err;
  
  #if defined(MADV_DONTDUMP)
    err = madvise(env->me_map, env->me_dxb_mmap.limit, MADV_DONTDUMP)
              ? ignore_enosys(errno)
              : MDBX_SUCCESS;
    if (unlikely(MDBX_IS_ERROR(err)))
      return err;
  #endif /* MADV_DONTDUMP */
  #if defined(MADV_DODUMP)
    if (mdbx_runtime_flags & MDBX_DBG_DUMP) {
      const size_t meta_length_aligned2os = pgno_align2os_bytes(env, NUM_METAS);
      err = madvise(env->me_map, meta_length_aligned2os, MADV_DODUMP)
                ? ignore_enosys(errno)
                : MDBX_SUCCESS;
      if (unlikely(MDBX_IS_ERROR(err)))
        return err;
    }
  #endif /* MADV_DODUMP */
  
  #ifdef MDBX_USE_VALGRIND
    env->me_valgrind_handle =
        VALGRIND_CREATE_BLOCK(env->me_map, env->me_dxb_mmap.limit, "mdbx");
  #endif /* MDBX_USE_VALGRIND */
  
    mdbx_assert(env, used_bytes >= pgno2bytes(env, NUM_METAS) &&
                         used_bytes <= env->me_dxb_mmap.limit);
  #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
    VALGRIND_MAKE_MEM_NOACCESS(env->me_map + used_bytes,
                               env->me_dxb_mmap.limit - used_bytes);
    ASAN_POISON_MEMORY_REGION(env->me_map + used_bytes,
                              env->me_dxb_mmap.limit - used_bytes);
    env->me_poison_edge = bytes2pgno(env, env->me_dxb_mmap.limit);
  #endif /* MDBX_USE_VALGRIND || __SANITIZE_ADDRESS__ */
  
    const unsigned meta_clash_mask = mdbx_meta_eq_mask(env);
    if (unlikely(meta_clash_mask)) {
      if (/* not recovery mode */ env->me_stuck_meta < 0) {
        mdbx_error("meta-pages are clashed: mask 0x%d", meta_clash_mask);
        return MDBX_CORRUPTED;
      } else {
        mdbx_warning("ignore meta-pages clashing (mask 0x%d) in recovery mode",
                     meta_clash_mask);
      }
    }
  
    while (likely(/* not recovery mode */ env->me_stuck_meta < 0)) {
      MDBX_meta *const head = mdbx_meta_head(env);
      const txnid_t head_txnid = mdbx_meta_txnid_fluid(env, head);
      MDBX_meta *const steady = mdbx_meta_steady(env);
      const txnid_t steady_txnid = mdbx_meta_txnid_fluid(env, steady);
      if (head_txnid == steady_txnid)
        break;
  
      if (lck_rc == /* lck exclusive */ MDBX_RESULT_TRUE) {
        mdbx_assert(env, META_IS_STEADY(&meta) && !META_IS_STEADY(head));
        if (meta_bootid_match(head)) {
          MDBX_meta clone = *head;
          uint64_t filesize = env->me_dbgeo.now;
          err = mdbx_validate_meta(
              env, &clone, &filesize, data_page(head),
              bytes2pgno(env, (uint8_t *)data_page(head) - env->me_map), nullptr,
              env->me_psize);
          if (err == MDBX_SUCCESS) {
            mdbx_warning(
                "opening after an unclean shutdown, but boot-id(%016" PRIx64
                "-%016" PRIx64
                ") is MATCH: rollback NOT needed, steady-sync NEEDED%s",
                bootid.x, bootid.y,
                (env->me_flags & MDBX_RDONLY) ? ", but unable in read-only mode"
                                              : "");
            if (env->me_flags & MDBX_RDONLY)
              return MDBX_WANNA_RECOVERY /* LY: could not recovery/sync */;
            meta = clone;
            *env->me_unsynced_pages = meta.mm_geo.next;
            break;
          }
          mdbx_warning("opening after an unclean shutdown, "
                       "but boot-id(%016" PRIx64 "-%016" PRIx64 ") is MATCH, "
                       "but last meta not valid, rollback needed",
                       bootid.x, bootid.y);
        }
        if (env->me_flags & MDBX_RDONLY) {
          mdbx_error("rollback needed: (from head %" PRIaTXN
                     " to steady %" PRIaTXN "), but unable in read-only mode",
                     head_txnid, steady_txnid);
          return MDBX_WANNA_RECOVERY /* LY: could not recovery/rollback */;
        }
  
        const MDBX_meta *const meta0 = METAPAGE(env, 0);
        const MDBX_meta *const meta1 = METAPAGE(env, 1);
        const MDBX_meta *const meta2 = METAPAGE(env, 2);
        txnid_t undo_txnid = 0 /* zero means undo is unneeded */;
        while (
            (head != meta0 && mdbx_meta_txnid_fluid(env, meta0) == undo_txnid) ||
            (head != meta1 && mdbx_meta_txnid_fluid(env, meta1) == undo_txnid) ||
            (head != meta2 && mdbx_meta_txnid_fluid(env, meta2) == undo_txnid))
          undo_txnid = safe64_txnid_next(undo_txnid);
        if (unlikely(undo_txnid >= steady_txnid)) {
          mdbx_fatal("rollback failed: no suitable txnid (0,1,2) < %" PRIaTXN,
                     steady_txnid);
          return MDBX_PANIC /* LY: could not recovery/rollback */;
        }
  
        /* LY: rollback weak checkpoint */
        mdbx_notice("rollback: from %" PRIaTXN ", to %" PRIaTXN " as %" PRIaTXN,
                    head_txnid, steady_txnid, undo_txnid);
        mdbx_ensure(env, head_txnid == mdbx_meta_txnid_stable(env, head));
  
        if (env->me_flags & MDBX_WRITEMAP) {
          /* It is possible to update txnid without safe64_write(),
           * since DB opened exclusive for now */
          head->mm_txnid_a.inconsistent = undo_txnid;
          head->mm_datasync_sign = MDBX_DATASIGN_WEAK;
          head->mm_txnid_b.inconsistent = undo_txnid;
          const size_t offset = (uint8_t *)data_page(head) - env->me_dxb_mmap.dxb;
          const size_t paged_offset = floor_powerof2(offset, env->me_os_psize);
          const size_t paged_length = ceil_powerof2(
              env->me_psize + offset - paged_offset, env->me_os_psize);
          err = mdbx_msync(&env->me_dxb_mmap, paged_offset, paged_length, false);
        } else {
          MDBX_meta rollback = *head;
          mdbx_meta_set_txnid(env, &rollback, undo_txnid);
          rollback.mm_datasync_sign = MDBX_DATASIGN_WEAK;
          err = mdbx_pwrite(env->me_lazy_fd, &rollback, sizeof(MDBX_meta),
                            (uint8_t *)head - (uint8_t *)env->me_map);
        }
        if (err) {
          mdbx_error("error %d rollback from %" PRIaTXN ", to %" PRIaTXN
                     " as %" PRIaTXN,
                     err, head_txnid, steady_txnid, undo_txnid);
          return err;
        }
  
        mdbx_flush_incoherent_mmap(env->me_map, pgno2bytes(env, NUM_METAS),
                                   env->me_os_psize);
        mdbx_ensure(env, undo_txnid == mdbx_meta_txnid_fluid(env, head));
        mdbx_ensure(env, 0 == mdbx_meta_eq_mask(env));
        continue;
      }
  
      if (!env->me_lck) {
        /* LY: without-lck (read-only) mode, so it is impossible that other
         * process made weak checkpoint. */
        mdbx_error("%s", "without-lck, unable recovery/rollback");
        return MDBX_WANNA_RECOVERY;
      }
  
      /* LY: assume just have a collision with other running process,
       *     or someone make a weak checkpoint */
      mdbx_verbose("%s", "assume collision or online weak checkpoint");
      break;
    }
  
    const MDBX_meta *head = mdbx_meta_head(env);
    if (lck_rc == /* lck exclusive */ MDBX_RESULT_TRUE) {
      /* re-check size after mmap */
      if ((env->me_dxb_mmap.current & (env->me_os_psize - 1)) != 0 ||
          env->me_dxb_mmap.current < used_bytes) {
        mdbx_error("unacceptable/unexpected datafile size %" PRIuPTR,
                   env->me_dxb_mmap.current);
        return MDBX_PROBLEM;
      }
      if (env->me_dxb_mmap.current != env->me_dbgeo.now) {
        meta.mm_geo.now = bytes2pgno(env, env->me_dxb_mmap.current);
        mdbx_notice("need update meta-geo to filesize %" PRIuPTR
                    " bytes, %" PRIaPGNO " pages",
                    env->me_dxb_mmap.current, meta.mm_geo.now);
      }
  
      if (memcmp(&meta.mm_geo, &head->mm_geo, sizeof(meta.mm_geo))) {
        if ((env->me_flags & MDBX_RDONLY) != 0 ||
            /* recovery mode */ env->me_stuck_meta >= 0) {
          mdbx_warning("skipped update meta.geo in %s mode: from l%" PRIaPGNO
                       "-n%" PRIaPGNO "-u%" PRIaPGNO "/s%u-g%u, to l%" PRIaPGNO
                       "-n%" PRIaPGNO "-u%" PRIaPGNO "/s%u-g%u",
                       (env->me_stuck_meta < 0) ? "read-only" : "recovery",
                       head->mm_geo.lower, head->mm_geo.now, head->mm_geo.upper,
                       head->mm_geo.shrink, head->mm_geo.grow, meta.mm_geo.lower,
                       meta.mm_geo.now, meta.mm_geo.upper, meta.mm_geo.shrink,
                       meta.mm_geo.grow);
        } else {
          const txnid_t txnid = mdbx_meta_txnid_stable(env, head);
          const txnid_t next_txnid = safe64_txnid_next(txnid);
          if (unlikely(txnid > MAX_TXNID)) {
            mdbx_error("%s", "txnid overflow!");
            return MDBX_TXN_FULL;
          }
          mdbx_notice("updating meta.geo: "
                      "from l%" PRIaPGNO "-n%" PRIaPGNO "-u%" PRIaPGNO
                      "/s%u-g%u (txn#%" PRIaTXN "), "
                      "to l%" PRIaPGNO "-n%" PRIaPGNO "-u%" PRIaPGNO
                      "/s%u-g%u (txn#%" PRIaTXN ")",
                      head->mm_geo.lower, head->mm_geo.now, head->mm_geo.upper,
                      head->mm_geo.shrink, head->mm_geo.grow, txnid,
                      meta.mm_geo.lower, meta.mm_geo.now, meta.mm_geo.upper,
                      meta.mm_geo.shrink, meta.mm_geo.grow, next_txnid);
  
          mdbx_ensure(env, mdbx_meta_eq(env, &meta, head));
          mdbx_meta_set_txnid(env, &meta, next_txnid);
          err = mdbx_sync_locked(env, env->me_flags | MDBX_SHRINK_ALLOWED, &meta);
          if (err) {
            mdbx_error("error %d, while updating meta.geo: "
                       "from l%" PRIaPGNO "-n%" PRIaPGNO "-u%" PRIaPGNO
                       "/s%u-g%u (txn#%" PRIaTXN "), "
                       "to l%" PRIaPGNO "-n%" PRIaPGNO "-u%" PRIaPGNO
                       "/s%u-g%u (txn#%" PRIaTXN ")",
                       err, head->mm_geo.lower, head->mm_geo.now,
                       head->mm_geo.upper, head->mm_geo.shrink, head->mm_geo.grow,
                       txnid, meta.mm_geo.lower, meta.mm_geo.now,
                       meta.mm_geo.upper, meta.mm_geo.shrink, meta.mm_geo.grow,
                       next_txnid);
            return err;
          }
        }
      }
    }
  
    *env->me_discarded_tail = bytes2pgno(env, used_aligned2os_bytes);
    if (used_aligned2os_bytes < env->me_dxb_mmap.current) {
  #if defined(MADV_REMOVE)
      if (lck_rc && (env->me_flags & MDBX_WRITEMAP) != 0 &&
          /* not recovery mode */ env->me_stuck_meta < 0) {
        mdbx_notice("open-MADV_%s %u..%u", "REMOVE (deallocate file space)",
                    *env->me_discarded_tail,
                    bytes2pgno(env, env->me_dxb_mmap.current));
        err =
            madvise(env->me_map + used_aligned2os_bytes,
                    env->me_dxb_mmap.current - used_aligned2os_bytes, MADV_REMOVE)
                ? ignore_enosys(errno)
                : MDBX_SUCCESS;
        if (unlikely(MDBX_IS_ERROR(err)))
          return err;
      }
  #endif /* MADV_REMOVE */
  #if defined(MADV_DONTNEED)
      mdbx_notice("open-MADV_%s %u..%u", "DONTNEED", *env->me_discarded_tail,
                  bytes2pgno(env, env->me_dxb_mmap.current));
      err =
          madvise(env->me_map + used_aligned2os_bytes,
                  env->me_dxb_mmap.current - used_aligned2os_bytes, MADV_DONTNEED)
              ? ignore_enosys(errno)
              : MDBX_SUCCESS;
      if (unlikely(MDBX_IS_ERROR(err)))
        return err;
  #elif defined(POSIX_MADV_DONTNEED)
      err = ignore_enosys(posix_madvise(
          env->me_map + used_aligned2os_bytes,
          env->me_dxb_mmap.current - used_aligned2os_bytes, POSIX_MADV_DONTNEED));
      if (unlikely(MDBX_IS_ERROR(err)))
        return err;
  #elif defined(POSIX_FADV_DONTNEED)
      err = ignore_enosys(posix_fadvise(
          env->me_lazy_fd, used_aligned2os_bytes,
          env->me_dxb_mmap.current - used_aligned2os_bytes, POSIX_FADV_DONTNEED));
      if (unlikely(MDBX_IS_ERROR(err)))
        return err;
  #endif /* MADV_DONTNEED */
    }
  
    err = mdbx_set_readahead(env, 0, used_bytes, readahead);
    if (err != MDBX_SUCCESS && lck_rc == /* lck exclusive */ MDBX_RESULT_TRUE)
      return err;
  
    return rc;
  }
  
  /******************************************************************************/
  
  /* Open and/or initialize the lock region for the environment. */
  static __cold int mdbx_setup_lck(MDBX_env *env, char *lck_pathname,
                                   mdbx_mode_t mode) {
    mdbx_assert(env, env->me_lazy_fd != INVALID_HANDLE_VALUE);
    mdbx_assert(env, env->me_lfd == INVALID_HANDLE_VALUE);
  
    int err = mdbx_openfile(MDBX_OPEN_LCK, env, lck_pathname, &env->me_lfd, mode);
    if (err != MDBX_SUCCESS) {
      if (!(err == MDBX_ENOFILE && (env->me_flags & MDBX_EXCLUSIVE)) &&
          !((err == MDBX_EROFS || err == MDBX_EACCESS || err == MDBX_EPERM) &&
            (env->me_flags & MDBX_RDONLY)))
        return err;
  
      /* ensure the file system is read-only */
      err = mdbx_check_fs_rdonly(env->me_lazy_fd, lck_pathname, err);
      if (err != MDBX_SUCCESS &&
          /* ignore ERROR_NOT_SUPPORTED for exclusive mode */
          !(err == MDBX_ENOSYS && (env->me_flags & MDBX_EXCLUSIVE)))
        return err;
  
      /* LY: without-lck mode (e.g. exclusive or on read-only filesystem) */
      /* beginning of a locked section ---------------------------------------- */
      lcklist_lock();
      mdbx_assert(env, env->me_lcklist_next == nullptr);
      env->me_lfd = INVALID_HANDLE_VALUE;
      const int rc = mdbx_lck_seize(env);
      if (MDBX_IS_ERROR(rc)) {
        /* Calling lcklist_detach_locked() is required to restore POSIX-filelock
         * and this job will be done by mdbx_env_close0(). */
        lcklist_unlock();
        return rc;
      }
      /* insert into inprocess lck-list */
      env->me_lcklist_next = inprocess_lcklist_head;
      inprocess_lcklist_head = env;
      lcklist_unlock();
      /* end of a locked section ---------------------------------------------- */
  
      env->me_oldest = &env->me_lckless_stub.oldest;
      env->me_sync_timestamp = &env->me_lckless_stub.sync_timestamp;
      env->me_autosync_period = &env->me_lckless_stub.autosync_period;
      env->me_unsynced_pages = &env->me_lckless_stub.autosync_pending;
      env->me_autosync_threshold = &env->me_lckless_stub.autosync_threshold;
      env->me_discarded_tail = &env->me_lckless_stub.discarded_tail;
      env->me_meta_sync_txnid = &env->me_lckless_stub.meta_sync_txnid;
      env->me_maxreaders = UINT_MAX;
  #if MDBX_LOCKING > 0
      env->me_wlock = &env->me_lckless_stub.wlock;
  #endif /* MDBX_LOCKING > 0 */
      mdbx_debug("lck-setup:%s%s%s", " lck-less",
                 (env->me_flags & MDBX_RDONLY) ? " readonly" : "",
                 (rc == MDBX_RESULT_TRUE) ? " exclusive" : " cooperative");
      return rc;
    }
  
    /* beginning of a locked section ------------------------------------------ */
    lcklist_lock();
    mdbx_assert(env, env->me_lcklist_next == nullptr);
  
    /* Try to get exclusive lock. If we succeed, then
     * nobody is using the lock region and we should initialize it. */
    err = mdbx_lck_seize(env);
    if (MDBX_IS_ERROR(err)) {
    bailout:
      /* Calling lcklist_detach_locked() is required to restore POSIX-filelock
       * and this job will be done by mdbx_env_close0(). */
      lcklist_unlock();
      return err;
    }
  
    MDBX_env *inprocess_neighbor = nullptr;
    if (err == MDBX_RESULT_TRUE) {
      err = uniq_check(&env->me_lck_mmap, &inprocess_neighbor);
      if (MDBX_IS_ERROR(err))
        goto bailout;
      if (inprocess_neighbor &&
          ((mdbx_runtime_flags & MDBX_DBG_LEGACY_MULTIOPEN) == 0 ||
           (inprocess_neighbor->me_flags & MDBX_EXCLUSIVE) != 0)) {
        err = MDBX_BUSY;
        goto bailout;
      }
    }
    const int lck_seize_rc = err;
  
    mdbx_debug("lck-setup:%s%s%s", " with-lck",
               (env->me_flags & MDBX_RDONLY) ? " readonly" : "",
               (lck_seize_rc == MDBX_RESULT_TRUE) ? " exclusive"
                                                  : " cooperative");
  
    uint64_t size = 0;
    err = mdbx_filesize(env->me_lfd, &size);
    if (unlikely(err != MDBX_SUCCESS))
      goto bailout;
  
    if (lck_seize_rc == MDBX_RESULT_TRUE) {
      size = ceil_powerof2(env->me_maxreaders * sizeof(MDBX_reader) +
                               sizeof(MDBX_lockinfo),
                           env->me_os_psize);
      mdbx_jitter4testing(false);
    } else {
      if (env->me_flags & MDBX_EXCLUSIVE) {
        err = MDBX_BUSY;
        goto bailout;
      }
      if (size > INT_MAX || (size & (env->me_os_psize - 1)) != 0 ||
          size < env->me_os_psize) {
        mdbx_error("lck-file has invalid size %" PRIu64 " bytes", size);
        err = MDBX_PROBLEM;
        goto bailout;
      }
    }
  
    const size_t maxreaders =
        ((size_t)size - sizeof(MDBX_lockinfo)) / sizeof(MDBX_reader);
    if (size > 65536 || maxreaders < 2 || maxreaders > MDBX_READERS_LIMIT) {
      mdbx_error("lck-size too big (up to %" PRIuPTR " readers)", maxreaders);
      err = MDBX_PROBLEM;
      goto bailout;
    }
    env->me_maxreaders = (unsigned)maxreaders;
  
    err = mdbx_mmap((env->me_flags & MDBX_EXCLUSIVE) | MDBX_WRITEMAP,
                    &env->me_lck_mmap, (size_t)size, (size_t)size,
                    lck_seize_rc ? MMAP_OPTION_TRUNCATE | MMAP_OPTION_SEMAPHORE
                                 : MMAP_OPTION_SEMAPHORE);
    if (unlikely(err != MDBX_SUCCESS))
      goto bailout;
  
  #ifdef MADV_DODUMP
    err = madvise(env->me_lck, size, MADV_DODUMP) ? ignore_enosys(errno)
                                                  : MDBX_SUCCESS;
    if (unlikely(MDBX_IS_ERROR(err)))
      goto bailout;
  #endif /* MADV_DODUMP */
  
  #ifdef MADV_WILLNEED
    err = madvise(env->me_lck, size, MADV_WILLNEED) ? ignore_enosys(errno)
                                                    : MDBX_SUCCESS;
    if (unlikely(MDBX_IS_ERROR(err)))
      goto bailout;
  #endif /* MADV_WILLNEED */
  
    struct MDBX_lockinfo *const lck = env->me_lck;
    if (lck_seize_rc == MDBX_RESULT_TRUE) {
      /* LY: exclusive mode, check and reset lck content */
      memset(lck, 0, (size_t)size);
      mdbx_jitter4testing(false);
      lck->mti_magic_and_version = MDBX_LOCK_MAGIC;
      lck->mti_os_and_format = MDBX_LOCK_FORMAT;
      err = mdbx_msync(&env->me_lck_mmap, 0, (size_t)size, false);
      if (unlikely(err != MDBX_SUCCESS)) {
        mdbx_error("initial-%s for lck-file failed", "msync");
        goto bailout;
      }
      err = mdbx_fsync(env->me_lck_mmap.fd, MDBX_SYNC_SIZE);
      if (unlikely(err != MDBX_SUCCESS)) {
        mdbx_error("initial-%s for lck-file failed", "fsync");
        goto bailout;
      }
    } else {
      if (lck->mti_magic_and_version != MDBX_LOCK_MAGIC) {
        mdbx_error("%s", "lock region has invalid magic/version");
        err = ((lck->mti_magic_and_version >> 8) != MDBX_MAGIC)
                  ? MDBX_INVALID
                  : MDBX_VERSION_MISMATCH;
        goto bailout;
      }
      if (lck->mti_os_and_format != MDBX_LOCK_FORMAT) {
        mdbx_error("lock region has os/format 0x%" PRIx32 ", expected 0x%" PRIx32,
                   lck->mti_os_and_format, MDBX_LOCK_FORMAT);
        err = MDBX_VERSION_MISMATCH;
        goto bailout;
      }
    }
  
    err = mdbx_lck_init(env, inprocess_neighbor, lck_seize_rc);
    if (MDBX_IS_ERROR(err))
      goto bailout;
  
    mdbx_ensure(env, env->me_lcklist_next == nullptr);
    /* insert into inprocess lck-list */
    env->me_lcklist_next = inprocess_lcklist_head;
    inprocess_lcklist_head = env;
    lcklist_unlock();
    /* end of a locked section ------------------------------------------------ */
  
    mdbx_assert(env, !MDBX_IS_ERROR(lck_seize_rc));
    env->me_oldest = &lck->mti_oldest_reader;
    env->me_sync_timestamp = &lck->mti_sync_timestamp;
    env->me_autosync_period = &lck->mti_autosync_period;
    env->me_unsynced_pages = &lck->mti_unsynced_pages;
    env->me_autosync_threshold = &lck->mti_autosync_threshold;
    env->me_discarded_tail = &lck->mti_discarded_tail;
    env->me_meta_sync_txnid = &lck->mti_meta_sync_txnid;
  #if MDBX_LOCKING > 0
    env->me_wlock = &lck->mti_wlock;
  #endif /* MDBX_LOCKING > 0 */
    return lck_seize_rc;
  }
  
  __cold int mdbx_is_readahead_reasonable(size_t volume, intptr_t redundancy) {
    if (volume <= 1024 * 1024 * 4ul)
      return MDBX_RESULT_TRUE;
  
    const intptr_t pagesize = mdbx_syspagesize();
    if (unlikely(pagesize < MIN_PAGESIZE || !is_powerof2(pagesize)))
      return MDBX_INCOMPATIBLE;
  
  #if defined(_WIN32) || defined(_WIN64)
    MEMORYSTATUSEX info;
    memset(&info, 0, sizeof(info));
    info.dwLength = sizeof(info);
    if (!GlobalMemoryStatusEx(&info))
      return GetLastError();
  #endif
    const int log2page = log2n(pagesize);
  
  #if defined(_WIN32) || defined(_WIN64)
    const intptr_t total_ram_pages = (intptr_t)(info.ullTotalPhys >> log2page);
  #elif defined(_SC_PHYS_PAGES)
    const intptr_t total_ram_pages = sysconf(_SC_PHYS_PAGES);
    if (total_ram_pages == -1)
      return errno;
  #elif defined(_SC_AIX_REALMEM)
    const intptr_t total_ram_Kb = sysconf(_SC_AIX_REALMEM);
    if (total_ram_Kb == -1)
      return errno;
    const intptr_t total_ram_pages = (total_ram_Kb << 10) >> log2page;
  #elif defined(HW_USERMEM) || defined(HW_PHYSMEM64) || defined(HW_MEMSIZE) ||   \
      defined(HW_PHYSMEM)
    size_t ram, len = sizeof(ram);
    static const int mib[] = {
      CTL_HW,
  #if defined(HW_USERMEM)
      HW_USERMEM
  #elif defined(HW_PHYSMEM64)
      HW_PHYSMEM64
  #elif defined(HW_MEMSIZE)
      HW_MEMSIZE
  #else
      HW_PHYSMEM
  #endif
    };
    if (sysctl(
  #ifdef SYSCTL_LEGACY_NONCONST_MIB
            (int *)
  #endif
                mib,
            ARRAY_LENGTH(mib), &ram, &len, NULL, 0) != 0)
      return errno;
    if (len != sizeof(ram))
      return MDBX_ENOSYS;
    const intptr_t total_ram_pages = (intptr_t)(ram >> log2page);
  #else
  #error "FIXME: Get User-accessible or physical RAM"
  #endif
    if (total_ram_pages < 1)
      return MDBX_ENOSYS;
  
    const intptr_t volume_pages = (volume + pagesize - 1) >> log2page;
    const intptr_t redundancy_pages =
        (redundancy < 0) ? -(intptr_t)((-redundancy + pagesize - 1) >> log2page)
                         : (intptr_t)(redundancy + pagesize - 1) >> log2page;
    if (volume_pages >= total_ram_pages ||
        volume_pages + redundancy_pages >= total_ram_pages)
      return MDBX_RESULT_FALSE;
  
  #if defined(_WIN32) || defined(_WIN64)
    const intptr_t avail_ram_pages = (intptr_t)(info.ullAvailPhys >> log2page);
  #elif defined(_SC_AVPHYS_PAGES)
    const intptr_t avail_ram_pages = sysconf(_SC_AVPHYS_PAGES);
    if (avail_ram_pages == -1)
      return errno;
  #elif defined(__MACH__)
    mach_msg_type_number_t count = HOST_VM_INFO_COUNT;
    vm_statistics_data_t vmstat;
    mach_port_t mport = mach_host_self();
    kern_return_t kerr = host_statistics(mach_host_self(), HOST_VM_INFO,
                                         (host_info_t)&vmstat, &count);
    mach_port_deallocate(mach_task_self(), mport);
    if (unlikely(kerr != KERN_SUCCESS))
      return MDBX_ENOSYS;
    const intptr_t avail_ram_pages = vmstat.free_count;
  #elif defined(VM_TOTAL) || defined(VM_METER)
    struct vmtotal info;
    size_t len = sizeof(info);
    static const int mib[] = {
      CTL_VM,
  #if defined(VM_TOTAL)
      VM_TOTAL
  #elif defined(VM_METER)
      VM_METER
  #endif
    };
    if (sysctl(
  #ifdef SYSCTL_LEGACY_NONCONST_MIB
            (int *)
  #endif
                mib,
            ARRAY_LENGTH(mib), &info, &len, NULL, 0) != 0)
      return errno;
    if (len != sizeof(info))
      return MDBX_ENOSYS;
    const intptr_t avail_ram_pages = info.t_free;
  #else
  #error "FIXME: Get Available RAM"
  #endif
    if (avail_ram_pages < 1)
      return MDBX_ENOSYS;
  
    return (volume_pages + redundancy_pages >= avail_ram_pages)
               ? MDBX_RESULT_FALSE
               : MDBX_RESULT_TRUE;
  }
  
  /* Merge sync flags */
  static uint32_t merge_sync_flags(const uint32_t a, const uint32_t b) {
    uint32_t r = a | b;
  
    /* avoid false MDBX_UTTERLY_NOSYNC */
    if (F_ISSET(r, MDBX_UTTERLY_NOSYNC) && !F_ISSET(a, MDBX_UTTERLY_NOSYNC) &&
        !F_ISSET(b, MDBX_UTTERLY_NOSYNC))
      r = (r - MDBX_UTTERLY_NOSYNC) | MDBX_SAFE_NOSYNC;
  
    /* convert MDBX_DEPRECATED_MAPASYNC to MDBX_SAFE_NOSYNC */
    if ((r & (MDBX_WRITEMAP | MDBX_DEPRECATED_MAPASYNC)) ==
            (MDBX_WRITEMAP | MDBX_DEPRECATED_MAPASYNC) &&
        !F_ISSET(r, MDBX_UTTERLY_NOSYNC))
      r = (r - MDBX_DEPRECATED_MAPASYNC) | MDBX_SAFE_NOSYNC;
  
    /* force MDBX_NOMETASYNC if MDBX_SAFE_NOSYNC enabled */
    if (r & MDBX_SAFE_NOSYNC)
      r |= MDBX_NOMETASYNC;
  
    assert(!(F_ISSET(r, MDBX_UTTERLY_NOSYNC) &&
             !F_ISSET(a, MDBX_UTTERLY_NOSYNC) &&
             !F_ISSET(b, MDBX_UTTERLY_NOSYNC)));
    return r;
  }
  
  __cold int mdbx_env_turn_for_recovery(MDBX_env *env, unsigned target_meta) {
    if (unlikely(target_meta >= NUM_METAS))
      return MDBX_EINVAL;
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if ((env->me_flags & (MDBX_EXCLUSIVE | MDBX_RDONLY)) != MDBX_EXCLUSIVE)
      return MDBX_EPERM;
  
    MDBX_page *page =
        (env->me_flags & MDBX_WRITEMAP)
            ? pgno2page(env, target_meta)
            : memcpy(env->me_pbuf, pgno2page(env, target_meta), env->me_psize);
    page->mp_pgno = target_meta;
    page->mp_flags = P_META;
  
    MDBX_meta *meta = page_meta(page);
    meta->mm_magic_and_version = MDBX_DATA_MAGIC;
    meta->mm_psize = env->me_psize;
    txnid_t txnid = mdbx_meta_txnid_stable(env, meta);
    const txnid_t txnid0 = mdbx_meta_txnid_stable(env, METAPAGE(env, 0));
    if (target_meta != 0 && txnid <= txnid0)
      txnid = safe64_txnid_next(txnid0);
    const txnid_t txnid1 = mdbx_meta_txnid_stable(env, METAPAGE(env, 1));
    if (target_meta != 1 && txnid <= txnid1)
      txnid = safe64_txnid_next(txnid1);
    const txnid_t txnid2 = mdbx_meta_txnid_stable(env, METAPAGE(env, 2));
    if (target_meta != 2 && txnid <= txnid2)
      txnid = safe64_txnid_next(txnid2);
  
    if (!META_IS_STEADY(meta) || mdbx_recent_committed_txnid(env) != txnid) {
      if (unlikely(txnid > MAX_TXNID)) {
        mdbx_error("%s", "txnid overflow!");
        return MDBX_TXN_FULL;
      }
      mdbx_meta_set_txnid(env, meta, txnid);
      meta->mm_datasync_sign = mdbx_meta_sign(meta);
    }
  
    if (env->me_flags & MDBX_WRITEMAP) {
      mdbx_flush_incoherent_cpu_writeback();
      rc = mdbx_msync(&env->me_dxb_mmap, 0, pgno_align2os_bytes(env, target_meta),
                      MDBX_SYNC_DATA | MDBX_SYNC_IODQ);
    } else {
      const mdbx_filehandle_t fd = (env->me_dsync_fd != INVALID_HANDLE_VALUE)
                                       ? env->me_dsync_fd
                                       : env->me_lazy_fd;
      rc = mdbx_pwrite(fd, page, env->me_psize, pgno2bytes(env, target_meta));
      if (rc == MDBX_SUCCESS && fd == env->me_lazy_fd)
        rc = mdbx_fsync(env->me_lazy_fd, MDBX_SYNC_DATA | MDBX_SYNC_IODQ);
    }
  
    return rc;
  }
  
  __cold int mdbx_env_open_for_recovery(MDBX_env *env, const char *pathname,
                                        unsigned target_meta, bool writeable) {
    if (unlikely(target_meta >= NUM_METAS))
      return MDBX_EINVAL;
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    env->me_stuck_meta = (int8_t)target_meta;
    return mdbx_env_open(
        env, pathname, writeable ? MDBX_EXCLUSIVE : MDBX_EXCLUSIVE | MDBX_RDONLY,
        0);
  }
  
  typedef struct {
    void *buffer_for_free;
    char *lck, *dxb;
    size_t ent_len;
  } MDBX_handle_env_pathname;
  
  __cold static int mdbx_handle_env_pathname(MDBX_handle_env_pathname *ctx,
                                             const char *pathname,
                                             MDBX_env_flags_t *flags,
                                             const mdbx_mode_t mode) {
    int rc;
    memset(ctx, 0, sizeof(*ctx));
    if (unlikely(!pathname))
      return MDBX_EINVAL;
  
  #if defined(_WIN32) || defined(_WIN64)
    const size_t wlen = mbstowcs(nullptr, pathname, INT_MAX);
    if (wlen < 1 || wlen > /* MAX_PATH */ INT16_MAX)
      return ERROR_INVALID_NAME;
    wchar_t *const pathnameW = _alloca((wlen + 1) * sizeof(wchar_t));
    if (wlen != mbstowcs(pathnameW, pathname, wlen + 1))
      return ERROR_INVALID_NAME;
  
    const DWORD dwAttrib = GetFileAttributesW(pathnameW);
    if (dwAttrib == INVALID_FILE_ATTRIBUTES) {
      rc = GetLastError();
      if (rc != MDBX_ENOFILE)
        return rc;
      if (mode == 0 || (*flags & MDBX_RDONLY) != 0)
        /* can't open existing */
        return rc;
  
      /* auto-create directory if requested */
      if ((*flags & MDBX_NOSUBDIR) == 0 &&
          !CreateDirectoryW(pathnameW, nullptr)) {
        rc = GetLastError();
        if (rc != ERROR_ALREADY_EXISTS)
          return rc;
      }
    } else {
      /* ignore passed MDBX_NOSUBDIR flag and set it automatically */
      *flags |= MDBX_NOSUBDIR;
      if (dwAttrib & FILE_ATTRIBUTE_DIRECTORY)
        *flags -= MDBX_NOSUBDIR;
    }
  #else
    struct stat st;
    if (stat(pathname, &st)) {
      rc = errno;
      if (rc != MDBX_ENOFILE)
        return rc;
      if (mode == 0 || (*flags & MDBX_RDONLY) != 0)
        /* can't open existing */
        return rc;
  
      /* auto-create directory if requested */
      const mdbx_mode_t dir_mode =
          (/* inherit read/write permissions for group and others */ mode &
           (S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH)) |
          /* always add read/write/search for owner */ S_IRWXU |
          ((mode & S_IRGRP) ? /* +search if readable by group */ S_IXGRP : 0) |
          ((mode & S_IROTH) ? /* +search if readable by others */ S_IXOTH : 0);
      if ((*flags & MDBX_NOSUBDIR) == 0 && mkdir(pathname, dir_mode)) {
        rc = errno;
        if (rc != EEXIST)
          return rc;
      }
    } else {
      /* ignore passed MDBX_NOSUBDIR flag and set it automatically */
      *flags |= MDBX_NOSUBDIR;
      if (S_ISDIR(st.st_mode))
        *flags -= MDBX_NOSUBDIR;
    }
  #endif
  
    static const char dxb_name[] = MDBX_DATANAME;
    static const size_t dxb_name_len = sizeof(dxb_name) - 1;
    static const char lck_name[] = MDBX_LOCKNAME;
    static const char lock_suffix[] = MDBX_LOCK_SUFFIX;
  
    ctx->ent_len = strlen(pathname);
    if ((*flags & MDBX_NOSUBDIR) && ctx->ent_len >= dxb_name_len &&
        !memcmp(dxb_name, pathname + ctx->ent_len - dxb_name_len, dxb_name_len)) {
      *flags -= MDBX_NOSUBDIR;
      ctx->ent_len -= dxb_name_len;
    }
  
    const size_t bytes_needed =
        ctx->ent_len * 2 + ((*flags & MDBX_NOSUBDIR)
                                ? sizeof(lock_suffix) + 1
                                : sizeof(lck_name) + sizeof(dxb_name));
    ctx->buffer_for_free = mdbx_malloc(bytes_needed);
    if (!ctx->buffer_for_free)
      return MDBX_ENOMEM;
  
    ctx->lck = ctx->buffer_for_free;
    if (*flags & MDBX_NOSUBDIR) {
      ctx->dxb = ctx->lck + ctx->ent_len + sizeof(lock_suffix);
      sprintf(ctx->lck, "%s%s", pathname, lock_suffix);
      strcpy(ctx->dxb, pathname);
    } else {
      ctx->dxb = ctx->lck + ctx->ent_len + sizeof(lck_name);
      sprintf(ctx->lck, "%.*s%s", (int)ctx->ent_len, pathname, lck_name);
      sprintf(ctx->dxb, "%.*s%s", (int)ctx->ent_len, pathname, dxb_name);
    }
  
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_env_delete(const char *pathname, MDBX_env_delete_mode_t mode) {
    switch (mode) {
    default:
      return MDBX_EINVAL;
    case MDBX_ENV_JUST_DELETE:
    case MDBX_ENV_ENSURE_UNUSED:
    case MDBX_ENV_WAIT_FOR_UNUSED:
      break;
    }
  
    MDBX_env dummy_env;
    memset(&dummy_env, 0, sizeof(dummy_env));
    dummy_env.me_flags =
        (mode == MDBX_ENV_ENSURE_UNUSED) ? MDBX_EXCLUSIVE : MDBX_ENV_DEFAULTS;
    dummy_env.me_psize = dummy_env.me_os_psize = (unsigned)mdbx_syspagesize();
    dummy_env.me_pathname = (char *)pathname;
  
    MDBX_handle_env_pathname env_pathname;
    STATIC_ASSERT(sizeof(dummy_env.me_flags) == sizeof(MDBX_env_flags_t));
    int rc = MDBX_RESULT_TRUE,
        err = mdbx_handle_env_pathname(
            &env_pathname, pathname, (MDBX_env_flags_t *)&dummy_env.me_flags, 0);
    if (likely(err == MDBX_SUCCESS)) {
      mdbx_filehandle_t clk_handle = INVALID_HANDLE_VALUE,
                        dxb_handle = INVALID_HANDLE_VALUE;
      if (mode > MDBX_ENV_JUST_DELETE) {
        err = mdbx_openfile(MDBX_OPEN_DELETE, &dummy_env, env_pathname.dxb,
                            &dxb_handle, 0);
        err = (err == MDBX_ENOFILE) ? MDBX_SUCCESS : err;
        if (err == MDBX_SUCCESS) {
          err = mdbx_openfile(MDBX_OPEN_DELETE, &dummy_env, env_pathname.lck,
                              &clk_handle, 0);
          err = (err == MDBX_ENOFILE) ? MDBX_SUCCESS : err;
        }
        if (err == MDBX_SUCCESS && clk_handle != INVALID_HANDLE_VALUE)
          err = mdbx_lockfile(clk_handle, mode == MDBX_ENV_WAIT_FOR_UNUSED);
        if (err == MDBX_SUCCESS && dxb_handle != INVALID_HANDLE_VALUE)
          err = mdbx_lockfile(dxb_handle, mode == MDBX_ENV_WAIT_FOR_UNUSED);
      }
  
      if (err == MDBX_SUCCESS) {
        err = mdbx_removefile(env_pathname.dxb);
        if (err == MDBX_SUCCESS)
          rc = MDBX_SUCCESS;
        else if (err == MDBX_ENOFILE)
          err = MDBX_SUCCESS;
      }
  
      if (err == MDBX_SUCCESS) {
        err = mdbx_removefile(env_pathname.lck);
        if (err == MDBX_SUCCESS)
          rc = MDBX_SUCCESS;
        else if (err == MDBX_ENOFILE)
          err = MDBX_SUCCESS;
      }
  
      if (err == MDBX_SUCCESS && !(dummy_env.me_flags & MDBX_NOSUBDIR)) {
        err = mdbx_removedirectory(pathname);
        if (err == MDBX_SUCCESS)
          rc = MDBX_SUCCESS;
        else if (err == MDBX_ENOFILE)
          err = MDBX_SUCCESS;
      }
  
      if (dxb_handle != INVALID_HANDLE_VALUE)
        mdbx_closefile(dxb_handle);
      if (clk_handle != INVALID_HANDLE_VALUE)
        mdbx_closefile(clk_handle);
    } else if (err == MDBX_ENOFILE)
      err = MDBX_SUCCESS;
  
    mdbx_free(env_pathname.buffer_for_free);
    return (err == MDBX_SUCCESS) ? rc : err;
  }
  
  __cold int mdbx_env_open(MDBX_env *env, const char *pathname,
                           MDBX_env_flags_t flags, mdbx_mode_t mode) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (flags & ~ENV_USABLE_FLAGS)
      return MDBX_EINVAL;
  
    if (env->me_lazy_fd != INVALID_HANDLE_VALUE ||
        (env->me_flags & MDBX_ENV_ACTIVE) != 0)
      return MDBX_EPERM;
  
    /* pickup previously mdbx_env_set_flags(),
     * but avoid MDBX_UTTERLY_NOSYNC by disjunction */
    const uint32_t saved_me_flags = env->me_flags;
    flags = merge_sync_flags(flags, env->me_flags);
  
    MDBX_handle_env_pathname env_pathname;
    rc = mdbx_handle_env_pathname(&env_pathname, pathname, &flags, mode);
    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout;
  
    if (flags & MDBX_RDONLY) {
      /* LY: silently ignore irrelevant flags when
       * we're only getting read access */
      flags &= ~(MDBX_WRITEMAP | MDBX_DEPRECATED_MAPASYNC | MDBX_SAFE_NOSYNC |
                 MDBX_NOMETASYNC | MDBX_COALESCE | MDBX_LIFORECLAIM |
                 MDBX_NOMEMINIT | MDBX_ACCEDE);
    } else {
  #if MDBX_MMAP_INCOHERENT_FILE_WRITE
      /* Temporary `workaround` for OpenBSD kernel's flaw.
       * See https://github.com/erthink/libmdbx/issues/67 */
      if ((flags & MDBX_WRITEMAP) == 0) {
        if (flags & MDBX_ACCEDE)
          flags |= MDBX_WRITEMAP;
        else {
          mdbx_debug_log(MDBX_LOG_ERROR, __func__, __LINE__,
                         "System (i.e. OpenBSD) requires MDBX_WRITEMAP because "
                         "of an internal flaw(s) in a file/buffer/page cache.\n");
          rc = 42 /* ENOPROTOOPT */;
          goto bailout;
        }
      }
  #endif /* MDBX_MMAP_INCOHERENT_FILE_WRITE */
      env->me_dirtylist = mdbx_calloc(MDBX_DPL_TXNFULL + 1, sizeof(MDBX_DP));
      if (!env->me_dirtylist)
        rc = MDBX_ENOMEM;
    }
  
    env->me_flags = (flags & ~MDBX_FATAL_ERROR) | MDBX_ENV_ACTIVE;
    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout;
  
    env->me_pathname = mdbx_calloc(env_pathname.ent_len + 1, 1);
    env->me_dbxs = mdbx_calloc(env->me_maxdbs, sizeof(MDBX_dbx));
    env->me_dbflags = mdbx_calloc(env->me_maxdbs, sizeof(env->me_dbflags[0]));
    env->me_dbiseqs = mdbx_calloc(env->me_maxdbs, sizeof(env->me_dbiseqs[0]));
    if (!(env->me_dbxs && env->me_pathname && env->me_dbflags &&
          env->me_dbiseqs)) {
      rc = MDBX_ENOMEM;
      goto bailout;
    }
    memcpy(env->me_pathname, env_pathname.dxb, env_pathname.ent_len);
    env->me_dbxs[FREE_DBI].md_cmp = cmp_int_align4; /* aligned MDBX_INTEGERKEY */
    env->me_dbxs[FREE_DBI].md_dcmp = cmp_lenfast;
  
    rc = mdbx_openfile(F_ISSET(flags, MDBX_RDONLY) ? MDBX_OPEN_DXB_READ
                                                   : MDBX_OPEN_DXB_LAZY,
                       env, env_pathname.dxb, &env->me_lazy_fd, mode);
    if (rc != MDBX_SUCCESS)
      goto bailout;
  
    mdbx_assert(env, env->me_dsync_fd == INVALID_HANDLE_VALUE);
    if ((flags & (MDBX_RDONLY | MDBX_SAFE_NOSYNC | MDBX_NOMETASYNC)) == 0) {
      rc = mdbx_openfile(MDBX_OPEN_DXB_DSYNC, env, env_pathname.dxb,
                         &env->me_dsync_fd, 0);
      mdbx_ensure(env, (rc != MDBX_SUCCESS) ==
                           (env->me_dsync_fd == INVALID_HANDLE_VALUE));
    }
  
  #if MDBX_LOCKING == MDBX_LOCKING_SYSV
    env->me_sysv_ipc.key = ftok(env_pathname.dxb, 42);
    if (env->me_sysv_ipc.key == -1) {
      rc = errno;
      goto bailout;
    }
  #endif /* MDBX_LOCKING */
  
  #if !(defined(_WIN32) || defined(_WIN64))
    if (mode == 0) {
      /* pickup mode for lck-file */
      struct stat st;
      if (fstat(env->me_lazy_fd, &st)) {
        rc = errno;
        goto bailout;
      }
      mode = st.st_mode;
    }
    mode = (/* inherit read permissions for group and others */ mode &
            (S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH)) |
           /* always add read/write/search for owner */ S_IRUSR | S_IWUSR |
           ((mode & S_IRGRP) ? /* +write if readable by group */ S_IWGRP : 0) |
           ((mode & S_IROTH) ? /* +write if readable by others */ S_IWOTH : 0);
  #endif /* !Windows */
    const int lck_rc = mdbx_setup_lck(env, env_pathname.lck, mode);
    if (MDBX_IS_ERROR(lck_rc)) {
      rc = lck_rc;
      goto bailout;
    }
  
    /* Set the position in files outside of the data to avoid corruption
     * due to erroneous use of file descriptors in the application code. */
    mdbx_fseek(env->me_lfd, UINT64_C(1) << 63);
    mdbx_fseek(env->me_lazy_fd, UINT64_C(1) << 63);
    if (env->me_dsync_fd != INVALID_HANDLE_VALUE)
      mdbx_fseek(env->me_dsync_fd, UINT64_C(1) << 63);
  
    const MDBX_env_flags_t rigorous_flags =
        MDBX_SAFE_NOSYNC | MDBX_DEPRECATED_MAPASYNC;
    const MDBX_env_flags_t mode_flags = rigorous_flags | MDBX_NOMETASYNC |
                                        MDBX_LIFORECLAIM | MDBX_COALESCE |
                                        MDBX_NORDAHEAD;
  
    if (env->me_lck && lck_rc != MDBX_RESULT_TRUE &&
        (env->me_flags & MDBX_RDONLY) == 0) {
      while (env->me_lck->mti_envmode == MDBX_RDONLY) {
        if (atomic_cas32(&env->me_lck->mti_envmode, MDBX_RDONLY,
                         env->me_flags & mode_flags))
          break;
        atomic_yield();
      }
  
      if (env->me_flags & MDBX_ACCEDE) {
        /* pickup current mode-flags, including MDBX_LIFORECLAIM |
         * MDBX_COALESCE | MDBX_NORDAHEAD */
        const unsigned diff =
            (env->me_lck->mti_envmode ^ env->me_flags) & mode_flags;
        mdbx_notice("accede mode-flags: 0x%X, 0x%X -> 0x%X", diff, env->me_flags,
                    env->me_flags ^ diff);
        env->me_flags ^= diff;
      }
  
      if ((env->me_lck->mti_envmode ^ env->me_flags) & rigorous_flags) {
        mdbx_error("%s", "current mode/flags incompatible with requested");
        rc = MDBX_INCOMPATIBLE;
        goto bailout;
      }
    }
  
    const int dxb_rc = mdbx_setup_dxb(env, lck_rc);
    if (MDBX_IS_ERROR(dxb_rc)) {
      rc = dxb_rc;
      goto bailout;
    }
  
    if (unlikely(/* recovery mode */ env->me_stuck_meta >= 0) &&
        (lck_rc != /* exclusive */ MDBX_RESULT_TRUE ||
         (flags & MDBX_EXCLUSIVE) == 0)) {
      mdbx_error("%s", "recovery requires exclusive mode");
      rc = MDBX_BUSY;
      goto bailout;
    }
  
    mdbx_debug("opened dbenv %p", (void *)env);
    if (env->me_lck) {
      if (lck_rc == MDBX_RESULT_TRUE) {
        env->me_lck->mti_envmode = env->me_flags & (mode_flags | MDBX_RDONLY);
        rc = mdbx_lck_downgrade(env);
        mdbx_debug("lck-downgrade-%s: rc %i",
                   (env->me_flags & MDBX_EXCLUSIVE) ? "partial" : "full", rc);
        if (rc != MDBX_SUCCESS)
          goto bailout;
      } else {
        rc = mdbx_cleanup_dead_readers(env, false, NULL);
        if (MDBX_IS_ERROR(rc))
          goto bailout;
      }
  
      if ((env->me_flags & MDBX_NOTLS) == 0) {
        rc = mdbx_rthc_alloc(&env->me_txkey, &env->me_lck->mti_readers[0],
                             &env->me_lck->mti_readers[env->me_maxreaders]);
        if (unlikely(rc != MDBX_SUCCESS))
          goto bailout;
        env->me_flags |= MDBX_ENV_TXKEY;
      }
    }
  
    if ((flags & MDBX_RDONLY) == 0) {
      const size_t tsize = sizeof(MDBX_txn),
                   size = tsize + env->me_maxdbs *
                                      (sizeof(MDBX_db) + sizeof(MDBX_cursor *) +
                                       sizeof(unsigned) + 1);
      rc = mdbx_memalign_alloc(
          env->me_os_psize,
          env->me_psize * (1 /* page buffer */ + 1 /* page killer buffer */),
          &env->me_pbuf);
      if (rc == MDBX_SUCCESS) {
        memset(env->me_pbuf, -1, env->me_psize * 2);
        MDBX_txn *txn = mdbx_calloc(1, size);
        if (txn) {
          txn->mt_dbs = (MDBX_db *)((char *)txn + tsize);
          txn->tw.cursors = (MDBX_cursor **)(txn->mt_dbs + env->me_maxdbs);
          txn->mt_dbiseqs = (unsigned *)(txn->tw.cursors + env->me_maxdbs);
          txn->mt_dbistate = (uint8_t *)(txn->mt_dbiseqs + env->me_maxdbs);
          txn->mt_env = env;
          txn->mt_dbxs = env->me_dbxs;
          txn->mt_flags = MDBX_TXN_FINISHED;
          env->me_txn0 = txn;
          txn->tw.retired_pages = mdbx_pnl_alloc(MDBX_PNL_INITIAL);
          txn->tw.reclaimed_pglist = mdbx_pnl_alloc(MDBX_PNL_INITIAL);
          if (!txn->tw.retired_pages || !txn->tw.reclaimed_pglist)
            rc = MDBX_ENOMEM;
        } else
          rc = MDBX_ENOMEM;
      }
    }
  
  #if MDBX_DEBUG
    if (rc == MDBX_SUCCESS) {
      MDBX_meta *meta = mdbx_meta_head(env);
      MDBX_db *db = &meta->mm_dbs[MAIN_DBI];
  
      mdbx_debug("opened database version %u, pagesize %u",
                 (uint8_t)meta->mm_magic_and_version, env->me_psize);
      mdbx_debug("using meta page %" PRIaPGNO ", txn %" PRIaTXN,
                 data_page(meta)->mp_pgno, mdbx_meta_txnid_fluid(env, meta));
      mdbx_debug("depth: %u", db->md_depth);
      mdbx_debug("entries: %" PRIu64, db->md_entries);
      mdbx_debug("branch pages: %" PRIaPGNO, db->md_branch_pages);
      mdbx_debug("leaf pages: %" PRIaPGNO, db->md_leaf_pages);
      mdbx_debug("overflow pages: %" PRIaPGNO, db->md_overflow_pages);
      mdbx_debug("root: %" PRIaPGNO, db->md_root);
      mdbx_debug("schema_altered: %" PRIaTXN, db->md_mod_txnid);
    }
  #endif
  
  bailout:
    if (rc != MDBX_SUCCESS) {
      rc = mdbx_env_close0(env) ? MDBX_PANIC : rc;
      env->me_flags =
          saved_me_flags | ((rc != MDBX_PANIC) ? 0 : MDBX_FATAL_ERROR);
    } else {
  #if defined(MDBX_USE_VALGRIND) || defined(__SANITIZE_ADDRESS__)
      mdbx_txn_valgrind(env, nullptr);
  #endif
    }
    mdbx_free(env_pathname.buffer_for_free);
    return rc;
  }
  
  /* Destroy resources from mdbx_env_open(), clear our readers & DBIs */
  static __cold int mdbx_env_close0(MDBX_env *env) {
    env->me_stuck_meta = -1;
    if (!(env->me_flags & MDBX_ENV_ACTIVE)) {
      mdbx_ensure(env, env->me_lcklist_next == nullptr);
      return MDBX_SUCCESS;
    }
  
    env->me_flags &= ~MDBX_ENV_ACTIVE;
    env->me_oldest = nullptr;
    env->me_sync_timestamp = nullptr;
    env->me_autosync_period = nullptr;
    env->me_unsynced_pages = nullptr;
    env->me_autosync_threshold = nullptr;
    env->me_discarded_tail = nullptr;
    env->me_meta_sync_txnid = nullptr;
    if (env->me_flags & MDBX_ENV_TXKEY)
      mdbx_rthc_remove(env->me_txkey);
  
    lcklist_lock();
    const int rc = lcklist_detach_locked(env);
    lcklist_unlock();
  
    if (env->me_map) {
      mdbx_munmap(&env->me_dxb_mmap);
  #ifdef MDBX_USE_VALGRIND
      VALGRIND_DISCARD(env->me_valgrind_handle);
      env->me_valgrind_handle = -1;
  #endif
    }
  
    if (env->me_dsync_fd != INVALID_HANDLE_VALUE) {
      (void)mdbx_closefile(env->me_dsync_fd);
      env->me_dsync_fd = INVALID_HANDLE_VALUE;
    }
  
    if (env->me_lazy_fd != INVALID_HANDLE_VALUE) {
      (void)mdbx_closefile(env->me_lazy_fd);
      env->me_lazy_fd = INVALID_HANDLE_VALUE;
    }
  
    if (env->me_lck)
      mdbx_munmap(&env->me_lck_mmap);
  
    if (env->me_lfd != INVALID_HANDLE_VALUE) {
      (void)mdbx_closefile(env->me_lfd);
      env->me_lfd = INVALID_HANDLE_VALUE;
    }
  
    if (env->me_dbxs) {
      for (unsigned i = env->me_numdbs; --i >= CORE_DBS;)
        mdbx_free(env->me_dbxs[i].md_name.iov_base);
      mdbx_free(env->me_dbxs);
    }
    mdbx_memalign_free(env->me_pbuf);
    mdbx_free(env->me_dbiseqs);
    mdbx_free(env->me_dbflags);
    mdbx_free(env->me_pathname);
    mdbx_free(env->me_dirtylist);
    if (env->me_txn0) {
      mdbx_txl_free(env->me_txn0->tw.lifo_reclaimed);
      mdbx_pnl_free(env->me_txn0->tw.retired_pages);
      mdbx_pnl_free(env->me_txn0->tw.spill_pages);
      mdbx_pnl_free(env->me_txn0->tw.reclaimed_pglist);
      mdbx_free(env->me_txn0);
    }
    env->me_flags = 0;
    return rc;
  }
  
  __cold int mdbx_env_close_ex(MDBX_env *env, bool dont_sync) {
    MDBX_page *dp;
    int rc = MDBX_SUCCESS;
  
    if (unlikely(!env))
      return MDBX_EINVAL;
  
    if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
      return MDBX_EBADSIGN;
  
  #if MDBX_ENV_CHECKPID || !(defined(_WIN32) || defined(_WIN64))
    /* Check the PID even if MDBX_ENV_CHECKPID=0 on non-Windows
     * platforms (i.e. where fork() is available).
     * This is required to legitimize a call after fork()
     * from a child process, that should be allowed to free resources. */
    if (unlikely(env->me_pid != mdbx_getpid()))
      env->me_flags |= MDBX_FATAL_ERROR;
  #endif /* MDBX_ENV_CHECKPID */
  
    if ((env->me_flags & (MDBX_RDONLY | MDBX_FATAL_ERROR)) == 0 && env->me_txn0) {
      if (env->me_txn0->mt_owner && env->me_txn0->mt_owner != mdbx_thread_self())
        return MDBX_BUSY;
    } else
      dont_sync = true;
  
    if (!atomic_cas32(&env->me_signature, MDBX_ME_SIGNATURE, 0))
      return MDBX_EBADSIGN;
  
    if (!dont_sync) {
  #if defined(_WIN32) || defined(_WIN64)
      /* On windows, without blocking is impossible to determine whether another
       * process is running a writing transaction or not.
       * Because in the "owner died" condition kernel don't release
       * file lock immediately. */
      rc = mdbx_env_sync_internal(env, true, false);
      rc = (rc == MDBX_RESULT_TRUE) ? MDBX_SUCCESS : rc;
  #else
      struct stat st;
      if (unlikely(fstat(env->me_lazy_fd, &st)))
        rc = errno;
      else if (st.st_nlink > 0 /* don't sync deleted files */) {
        rc = mdbx_env_sync_internal(env, true, true);
        rc = (rc == MDBX_BUSY || rc == EAGAIN || rc == EACCES || rc == EBUSY ||
              rc == EWOULDBLOCK || rc == MDBX_RESULT_TRUE)
                 ? MDBX_SUCCESS
                 : rc;
      }
  #endif
    }
  
    env->me_signature = 0;
    rc = mdbx_env_close0(env) ? MDBX_PANIC : rc;
    mdbx_ensure(env, mdbx_fastmutex_destroy(&env->me_dbi_lock) == MDBX_SUCCESS);
  #if defined(_WIN32) || defined(_WIN64)
    /* me_remap_guard don't have destructor (Slim Reader/Writer Lock) */
    DeleteCriticalSection(&env->me_windowsbug_lock);
  #else
    mdbx_ensure(env,
                mdbx_fastmutex_destroy(&env->me_remap_guard) == MDBX_SUCCESS);
  #endif /* Windows */
  
  #if MDBX_LOCKING > MDBX_LOCKING_SYSV
    mdbx_ensure(env, mdbx_ipclock_destroy(&env->me_lckless_stub.wlock) == 0);
  #endif /* MDBX_LOCKING */
  
    while ((dp = env->me_dpages) != NULL) {
      ASAN_UNPOISON_MEMORY_REGION(&dp->mp_next, sizeof(dp->mp_next));
      VALGRIND_MAKE_MEM_DEFINED(&dp->mp_next, sizeof(dp->mp_next));
      env->me_dpages = dp->mp_next;
      mdbx_free(dp);
    }
    VALGRIND_DESTROY_MEMPOOL(env);
    mdbx_ensure(env, env->me_lcklist_next == nullptr);
    env->me_pid = 0;
    mdbx_free(env);
  
    return rc;
  }
  
  __cold int mdbx_env_close(MDBX_env *env) {
    return __inline_mdbx_env_close(env);
  }
  
  /* Compare two items pointing at aligned unsigned int's. */
  static int __hot cmp_int_align4(const MDBX_val *a, const MDBX_val *b) {
    mdbx_assert(NULL, a->iov_len == b->iov_len);
    switch (a->iov_len) {
    case 4:
      return CMP2INT(unaligned_peek_u32(4, a->iov_base),
                     unaligned_peek_u32(4, b->iov_base));
    case 8:
      return CMP2INT(unaligned_peek_u64(4, a->iov_base),
                     unaligned_peek_u64(4, b->iov_base));
    default:
      mdbx_assert_fail(NULL, "invalid size for INTEGERKEY/INTEGERDUP", __func__,
                       __LINE__);
      return 0;
    }
  }
  
  /* Compare two items pointing at 2-byte aligned unsigned int's. */
  static int __hot cmp_int_align2(const MDBX_val *a, const MDBX_val *b) {
    mdbx_assert(NULL, a->iov_len == b->iov_len);
    switch (a->iov_len) {
    case 4:
      return CMP2INT(unaligned_peek_u32(2, a->iov_base),
                     unaligned_peek_u32(2, b->iov_base));
    case 8:
      return CMP2INT(unaligned_peek_u64(2, a->iov_base),
                     unaligned_peek_u64(2, b->iov_base));
    default:
      mdbx_assert_fail(NULL, "invalid size for INTEGERKEY/INTEGERDUP", __func__,
                       __LINE__);
      return 0;
    }
  }
  
  /* Compare two items pointing at unsigned values with unknown alignment.
   *
   * This is also set as MDBX_INTEGERDUP|MDBX_DUPFIXED's MDBX_dbx.md_dcmp. */
  static int __hot cmp_int_unaligned(const MDBX_val *a, const MDBX_val *b) {
    mdbx_assert(NULL, a->iov_len == b->iov_len);
    switch (a->iov_len) {
    case 4:
      return CMP2INT(unaligned_peek_u32(1, a->iov_base),
                     unaligned_peek_u32(1, b->iov_base));
    case 8:
      return CMP2INT(unaligned_peek_u64(1, a->iov_base),
                     unaligned_peek_u64(1, b->iov_base));
    default:
      mdbx_assert_fail(NULL, "invalid size for INTEGERKEY/INTEGERDUP", __func__,
                       __LINE__);
      return 0;
    }
  }
  
  /* Compare two items lexically */
  static int __hot cmp_lexical(const MDBX_val *a, const MDBX_val *b) {
    if (a->iov_len == b->iov_len)
      return memcmp(a->iov_base, b->iov_base, a->iov_len);
  
    const int diff_len = (a->iov_len < b->iov_len) ? -1 : 1;
    const size_t shortest = (a->iov_len < b->iov_len) ? a->iov_len : b->iov_len;
    int diff_data = memcmp(a->iov_base, b->iov_base, shortest);
    return likely(diff_data) ? diff_data : diff_len;
  }
  
  /* Compare two items in reverse byte order */
  static int __hot cmp_reverse(const MDBX_val *a, const MDBX_val *b) {
    const uint8_t *pa = (const uint8_t *)a->iov_base + a->iov_len;
    const uint8_t *pb = (const uint8_t *)b->iov_base + b->iov_len;
    const size_t shortest = (a->iov_len < b->iov_len) ? a->iov_len : b->iov_len;
  
    const uint8_t *const end = pa - shortest;
    while (pa != end) {
      int diff = *--pa - *--pb;
      if (likely(diff))
        return diff;
    }
    return CMP2INT(a->iov_len, b->iov_len);
  }
  
  /* Fast non-lexically comparator */
  static int __hot cmp_lenfast(const MDBX_val *a, const MDBX_val *b) {
    int diff = CMP2INT(a->iov_len, b->iov_len);
    return likely(diff) ? diff : memcmp(a->iov_base, b->iov_base, a->iov_len);
  }
  
  static bool unsure_equal(MDBX_cmp_func cmp, const MDBX_val *a,
                           const MDBX_val *b) {
    return cmp == cmp_lenfast || cmp == cmp_lexical || cmp == cmp_reverse ||
           cmp == cmp_int_unaligned || cmp_lenfast(a, b) == 0;
  }
  
  /* Search for key within a page, using binary search.
   * Returns the smallest entry larger or equal to the key.
   * If exactp is non-null, stores whether the found entry was an exact match
   * in *exactp (1 or 0).
   * Updates the cursor index with the index of the found entry.
   * If no entry larger or equal to the key is found, returns NULL. */
  static MDBX_node *__hot mdbx_node_search(MDBX_cursor *mc, const MDBX_val *key,
                                           int *exactp) {
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    const int nkeys = page_numkeys(mp);
    DKBUF;
  
    mdbx_debug("searching %u keys in %s %spage %" PRIaPGNO, nkeys,
               IS_LEAF(mp) ? "leaf" : "branch", IS_SUBP(mp) ? "sub-" : "",
               mp->mp_pgno);
  
    int low = IS_LEAF(mp) ? 0 : 1;
    int high = nkeys - 1;
    *exactp = 0;
    if (unlikely(high < low)) {
      mc->mc_ki[mc->mc_top] = 0;
      return NULL;
    }
  
    int rc = 0, i = 0;
    MDBX_cmp_func *cmp = mc->mc_dbx->md_cmp;
    MDBX_val nodekey;
    if (unlikely(IS_LEAF2(mp))) {
      mdbx_cassert(mc, mp->mp_leaf2_ksize == mc->mc_db->md_xsize);
      nodekey.iov_len = mp->mp_leaf2_ksize;
      do {
        i = (low + high) >> 1;
        nodekey.iov_base = page_leaf2key(mp, i, nodekey.iov_len);
        mdbx_cassert(mc, (char *)mp + mc->mc_txn->mt_env->me_psize >=
                             (char *)nodekey.iov_base + nodekey.iov_len);
        rc = cmp(key, &nodekey);
        mdbx_debug("found leaf index %u [%s], rc = %i", i, DKEY(&nodekey), rc);
        if (unlikely(rc == 0)) {
          *exactp = 1;
          break;
        }
        low = (rc < 0) ? low : i + 1;
        high = (rc < 0) ? i - 1 : high;
      } while (likely(low <= high));
  
      /* Found entry is less than the key. */
      /* Skip to get the smallest entry larger than key. */
      i += rc > 0;
  
      /* store the key index */
      mc->mc_ki[mc->mc_top] = (indx_t)i;
      return (i < nkeys)
                 ? /* fake for LEAF2 */ (MDBX_node *)(intptr_t)-1
                 : /* There is no entry larger or equal to the key. */ NULL;
    }
  
    if (cmp == cmp_int_align2 && IS_BRANCH(mp))
      /* Branch pages have no data, so if using integer keys,
       * alignment is guaranteed. Use faster mdbx_cmp_int_align4(). */
      cmp = cmp_int_align4;
  
    MDBX_node *node;
    do {
      i = (low + high) >> 1;
  
      node = page_node(mp, i);
      nodekey.iov_len = node_ks(node);
      nodekey.iov_base = node_key(node);
      mdbx_cassert(mc, (char *)mp + mc->mc_txn->mt_env->me_psize >=
                           (char *)nodekey.iov_base + nodekey.iov_len);
  
      rc = cmp(key, &nodekey);
      if (IS_LEAF(mp))
        mdbx_debug("found leaf index %u [%s], rc = %i", i, DKEY(&nodekey), rc);
      else
        mdbx_debug("found branch index %u [%s -> %" PRIaPGNO "], rc = %i", i,
                   DKEY(&nodekey), node_pgno(node), rc);
      if (unlikely(rc == 0)) {
        *exactp = 1;
        break;
      }
      low = (rc < 0) ? low : i + 1;
      high = (rc < 0) ? i - 1 : high;
    } while (likely(low <= high));
  
    /* Found entry is less than the key. */
    /* Skip to get the smallest entry larger than key. */
    i += rc > 0;
  
    /* store the key index */
    mc->mc_ki[mc->mc_top] = (indx_t)i;
    return (i < nkeys) ? page_node(mp, i)
                       : /* There is no entry larger or equal to the key. */ NULL;
  }
  
  #if 0 /* unused for now */
  static void mdbx_cursor_adjust(MDBX_cursor *mc, func) {
    MDBX_cursor *m2;
  
    for (m2 = mc->mc_txn->tw.cursors[mc->mc_dbi]; m2; m2 = m2->mc_next) {
      if (m2->mc_pg[m2->mc_top] == mc->mc_pg[mc->mc_top]) {
        func(mc, m2);
      }
    }
  }
  #endif
  
  /* Pop a page off the top of the cursor's stack. */
  static __inline void mdbx_cursor_pop(MDBX_cursor *mc) {
    if (mc->mc_snum) {
      mdbx_debug("popped page %" PRIaPGNO " off db %d cursor %p",
                 mc->mc_pg[mc->mc_top]->mp_pgno, DDBI(mc), (void *)mc);
      if (--mc->mc_snum) {
        mc->mc_top--;
      } else {
        mc->mc_flags &= ~C_INITIALIZED;
      }
    }
  }
  
  /* Push a page onto the top of the cursor's stack.
   * Set MDBX_TXN_ERROR on failure. */
  static __inline int mdbx_cursor_push(MDBX_cursor *mc, MDBX_page *mp) {
    mdbx_debug("pushing page %" PRIaPGNO " on db %d cursor %p", mp->mp_pgno,
               DDBI(mc), (void *)mc);
  
    if (unlikely(mc->mc_snum >= CURSOR_STACK)) {
      mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
      return MDBX_CURSOR_FULL;
    }
  
    mdbx_cassert(mc, mc->mc_snum < UINT16_MAX);
    mc->mc_top = mc->mc_snum++;
    mc->mc_pg[mc->mc_top] = mp;
    mc->mc_ki[mc->mc_top] = 0;
  
    return MDBX_SUCCESS;
  }
  
  /* Find the address of the page corresponding to a given page number.
   * Set MDBX_TXN_ERROR on failure.
   *
   * [in] mc    the cursor accessing the page.
   * [in] pgno  the page number for the page to retrieve.
   * [out] ret  address of a pointer where the page's address will be
   *            stored.
   * [out] lvl  dirtylist inheritance level of found page. 1=current txn,
   *            0=mapped page.
   *
   * Returns 0 on success, non-zero on failure. */
  __hot static int mdbx_page_get(MDBX_cursor *mc, pgno_t pgno, MDBX_page **ret,
                                 int *lvl, txnid_t pp_txnid) {
    MDBX_txn *txn = mc->mc_txn;
    if (unlikely(pgno >= txn->mt_next_pgno)) {
      mdbx_error("page #%" PRIaPGNO " beyond next-pgno", pgno);
    notfound:
      *ret = nullptr;
      txn->mt_flags |= MDBX_TXN_ERROR;
      return MDBX_PAGE_NOTFOUND;
    }
  
    MDBX_env *const env = txn->mt_env;
    MDBX_page *p = nullptr;
    mdbx_assert(env, ((txn->mt_flags ^ env->me_flags) & MDBX_WRITEMAP) == 0);
    mdbx_assert(env, pp_txnid >= MIN_TXNID && pp_txnid <= txn->mt_txnid);
    const uint16_t illegal_bits = (txn->mt_flags & MDBX_TXN_RDONLY)
                                      ? P_LOOSE | P_SUBP | P_META | P_DIRTY
                                      : P_LOOSE | P_SUBP | P_META;
    int level;
    if (unlikely((txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_WRITEMAP)) == 0)) {
      level = 1;
      do {
        /* Spilled pages were dirtied in this txn and flushed
         * because the dirty list got full. Bring this page
         * back in from the map (but don't unspill it here,
         * leave that unless page_touch happens again). */
        if (txn->tw.spill_pages &&
            mdbx_pnl_exist(txn->tw.spill_pages, pgno << 1)) {
          pp_txnid = txn->mt_txnid;
          goto spilled;
        }
        p = mdbx_dpl_find(txn->tw.dirtylist, pgno);
        if (p)
          goto dirty;
        level++;
      } while ((txn = txn->mt_parent) != NULL);
    }
    level = 0;
  
  spilled:
    p = pgno2page(env, pgno);
  
  dirty:
    *(lvl ? lvl : &level) = level;
    *ret = p;
  
    if (unlikely(p->mp_pgno != pgno)) {
      bad_page(
          p, "mismatch actual pgno (%" PRIaPGNO ") != expected (%" PRIaPGNO ")\n",
          p->mp_pgno, pgno);
      goto notfound;
    }
  
    if (unlikely(p->mp_flags & illegal_bits)) {
      bad_page(p, "invalid page's flags (%u)\n", p->mp_flags);
      goto corrupted;
    }
  
    if (unlikely(p->mp_txnid >
                 ((p->mp_flags & P_DIRTY) ? UINT64_MAX : pp_txnid))) {
      bad_page(p, "page mod-txnid (%" PRIaTXN ") > parent (%" PRIaTXN ")\n",
               p->mp_txnid, pp_txnid);
      goto corrupted;
    }
  
    if (unlikely((p->mp_upper < p->mp_lower ||
                  ((p->mp_lower | p->mp_upper) & 1) != 0 ||
                  PAGEHDRSZ + p->mp_upper > env->me_psize) &&
                 !IS_OVERFLOW(p))) {
      bad_page(p, "invalid page lower(%u)/upper(%u) with limit (%u)\n",
               p->mp_lower, p->mp_upper, page_space(env));
      goto corrupted;
    }
  
    if (mdbx_audit_enabled())
      return mdbx_page_check(mc, p, C_UPDATING);
  
    return MDBX_SUCCESS;
  
  corrupted:
    mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
    return MDBX_CORRUPTED;
  }
  
  /* Finish mdbx_page_search() / mdbx_page_search_lowest().
   * The cursor is at the root page, set up the rest of it. */
  __hot static int mdbx_page_search_root(MDBX_cursor *mc, const MDBX_val *key,
                                         int flags) {
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    int rc;
    DKBUF;
  
    while (IS_BRANCH(mp)) {
      MDBX_node *node;
      int i;
  
      mdbx_debug("branch page %" PRIaPGNO " has %u keys", mp->mp_pgno,
                 page_numkeys(mp));
      /* Don't assert on branch pages in the GC. We can get here
       * while in the process of rebalancing a GC branch page; we must
       * let that proceed. ITS#8336 */
      mdbx_cassert(mc, !mc->mc_dbi || page_numkeys(mp) > 1);
      mdbx_debug("found index 0 to page %" PRIaPGNO, node_pgno(page_node(mp, 0)));
  
      if (flags & (MDBX_PS_FIRST | MDBX_PS_LAST)) {
        i = 0;
        if (flags & MDBX_PS_LAST) {
          i = page_numkeys(mp) - 1;
          /* if already init'd, see if we're already in right place */
          if (mc->mc_flags & C_INITIALIZED) {
            if (mc->mc_ki[mc->mc_top] == i) {
              mc->mc_top = mc->mc_snum++;
              mp = mc->mc_pg[mc->mc_top];
              goto ready;
            }
          }
        }
      } else {
        int exact;
        node = mdbx_node_search(mc, key, &exact);
        if (node == NULL)
          i = page_numkeys(mp) - 1;
        else {
          i = mc->mc_ki[mc->mc_top];
          if (!exact) {
            mdbx_cassert(mc, i > 0);
            i--;
          }
        }
        mdbx_debug("following index %u for key [%s]", i, DKEY(key));
      }
  
      mdbx_cassert(mc, i < (int)page_numkeys(mp));
      node = page_node(mp, i);
  
      if (unlikely((rc = mdbx_page_get(mc, node_pgno(node), &mp, NULL,
                                       pp_txnid4chk(mp, mc->mc_txn))) != 0))
        return rc;
  
      mc->mc_ki[mc->mc_top] = (indx_t)i;
      if (unlikely(rc = mdbx_cursor_push(mc, mp)))
        return rc;
  
    ready:
      if (flags & MDBX_PS_MODIFY) {
        if (unlikely((rc = mdbx_page_touch(mc)) != 0))
          return rc;
        mp = mc->mc_pg[mc->mc_top];
      }
    }
  
    if (unlikely(!IS_LEAF(mp))) {
      mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
      return bad_page(mp, "index points to a page with 0x%02x flags\n",
                      mp->mp_flags);
    }
  
    mdbx_debug("found leaf page %" PRIaPGNO " for key [%s]", mp->mp_pgno,
               DKEY(key));
    mc->mc_flags |= C_INITIALIZED;
    mc->mc_flags &= ~C_EOF;
  
    return MDBX_SUCCESS;
  }
  
  static int mdbx_setup_dbx(MDBX_dbx *const dbx, const MDBX_db *const db,
                            const unsigned pagesize) {
    if (unlikely(!dbx->md_cmp)) {
      dbx->md_cmp = get_default_keycmp(db->md_flags);
      dbx->md_dcmp = get_default_datacmp(db->md_flags);
    }
  
    dbx->md_klen_min =
        (db->md_flags & MDBX_INTEGERKEY) ? 4 /* sizeof(uint32_t) */ : 0;
    dbx->md_klen_max = mdbx_limits_keysize_max(pagesize, db->md_flags);
    assert(dbx->md_klen_max != (unsigned)-1);
  
    dbx->md_vlen_min = (db->md_flags & MDBX_INTEGERDUP)
                           ? 4 /* sizeof(uint32_t) */
                           : ((db->md_flags & MDBX_DUPFIXED) ? 1 : 0);
    dbx->md_vlen_max = mdbx_limits_valsize_max(pagesize, db->md_flags);
    assert(dbx->md_vlen_max != (unsigned)-1);
  
    if ((db->md_flags & (MDBX_DUPFIXED | MDBX_INTEGERDUP)) != 0 && db->md_xsize) {
      if (unlikely(db->md_xsize < dbx->md_vlen_min ||
                   db->md_xsize > dbx->md_vlen_max)) {
        mdbx_error("db.md_xsize (%u) <> min/max value-length (%zu/%zu)",
                   db->md_xsize, dbx->md_vlen_min, dbx->md_vlen_max);
        return MDBX_CORRUPTED;
      }
      dbx->md_vlen_min = dbx->md_vlen_max = db->md_xsize;
    }
    return MDBX_SUCCESS;
  }
  
  static int mdbx_fetch_sdb(MDBX_txn *txn, MDBX_dbi dbi) {
    MDBX_cursor_couple couple;
    if (unlikely(TXN_DBI_CHANGED(txn, dbi)))
      return MDBX_BAD_DBI;
    int rc = mdbx_cursor_init(&couple.outer, txn, MAIN_DBI);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    MDBX_dbx *const dbx = &txn->mt_dbxs[dbi];
    rc = mdbx_page_search(&couple.outer, &dbx->md_name, 0);
    if (unlikely(rc != MDBX_SUCCESS))
      return (rc == MDBX_NOTFOUND) ? MDBX_BAD_DBI : rc;
  
    MDBX_val data;
    int exact = 0;
    MDBX_node *node = mdbx_node_search(&couple.outer, &dbx->md_name, &exact);
    if (unlikely(!exact))
      return MDBX_BAD_DBI;
    if (unlikely((node_flags(node) & (F_DUPDATA | F_SUBDATA)) != F_SUBDATA))
      return MDBX_INCOMPATIBLE; /* not a named DB */
  
    const txnid_t pp_txnid =
        pp_txnid4chk(couple.outer.mc_pg[couple.outer.mc_top], txn);
    rc = mdbx_node_read(&couple.outer, node, &data, pp_txnid);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(data.iov_len != sizeof(MDBX_db)))
      return MDBX_INCOMPATIBLE; /* not a named DB */
  
    uint16_t md_flags = UNALIGNED_PEEK_16(data.iov_base, MDBX_db, md_flags);
    /* The txn may not know this DBI, or another process may
     * have dropped and recreated the DB with other flags. */
    MDBX_db *const db = &txn->mt_dbs[dbi];
    if (unlikely((db->md_flags & DB_PERSISTENT_FLAGS) != md_flags))
      return MDBX_INCOMPATIBLE;
  
    memcpy(db, data.iov_base, sizeof(MDBX_db));
    mdbx_tassert(txn, txn->mt_txnid >= pp_txnid);
    if (unlikely(db->md_mod_txnid > pp_txnid)) {
      mdbx_error("db.md_mod_txnid (%" PRIaTXN ") > page-txnid (%" PRIaTXN ")",
                 db->md_mod_txnid, pp_txnid);
      return MDBX_CORRUPTED;
    }
    rc = mdbx_setup_dbx(dbx, db, txn->mt_env->me_psize);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    txn->mt_dbistate[dbi] &= ~DBI_STALE;
    return MDBX_SUCCESS;
  }
  
  /* Search for the lowest key under the current branch page.
   * This just bypasses a numkeys check in the current page
   * before calling mdbx_page_search_root(), because the callers
   * are all in situations where the current page is known to
   * be underfilled. */
  __hot static int mdbx_page_search_lowest(MDBX_cursor *mc) {
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    mdbx_cassert(mc, IS_BRANCH(mp));
    MDBX_node *node = page_node(mp, 0);
    int rc;
  
    if (unlikely((rc = mdbx_page_get(mc, node_pgno(node), &mp, NULL,
                                     pp_txnid4chk(mp, mc->mc_txn))) != 0))
      return rc;
  
    mc->mc_ki[mc->mc_top] = 0;
    if (unlikely(rc = mdbx_cursor_push(mc, mp)))
      return rc;
    return mdbx_page_search_root(mc, NULL, MDBX_PS_FIRST);
  }
  
  /* Search for the page a given key should be in.
   * Push it and its parent pages on the cursor stack.
   *
   * [in,out] mc  the cursor for this operation.
   * [in] key     the key to search for, or NULL for first/last page.
   * [in] flags   If MDBX_PS_MODIFY is set, visited pages in the DB
   *              are touched (updated with new page numbers).
   *              If MDBX_PS_FIRST or MDBX_PS_LAST is set, find first or last
   * leaf.
   *              This is used by mdbx_cursor_first() and mdbx_cursor_last().
   *              If MDBX_PS_ROOTONLY set, just fetch root node, no further
   *              lookups.
   *
   * Returns 0 on success, non-zero on failure. */
  __hot static int mdbx_page_search(MDBX_cursor *mc, const MDBX_val *key,
                                    int flags) {
    int rc;
    pgno_t root;
  
    /* Make sure the txn is still viable, then find the root from
     * the txn's db table and set it as the root of the cursor's stack. */
    if (unlikely(mc->mc_txn->mt_flags & MDBX_TXN_BLOCKED)) {
      mdbx_debug("%s", "transaction has failed, must abort");
      return MDBX_BAD_TXN;
    }
  
    /* Make sure we're using an up-to-date root */
    if (unlikely(*mc->mc_dbistate & DBI_STALE)) {
      rc = mdbx_fetch_sdb(mc->mc_txn, mc->mc_dbi);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
    root = mc->mc_db->md_root;
  
    if (unlikely(root == P_INVALID)) { /* Tree is empty. */
      mdbx_debug("%s", "tree is empty");
      return MDBX_NOTFOUND;
    }
  
    mdbx_cassert(mc, root >= NUM_METAS);
    if (!mc->mc_pg[0] || mc->mc_pg[0]->mp_pgno != root) {
      if (unlikely((rc = mdbx_page_get(
                        mc, root, &mc->mc_pg[0], NULL,
                        (/* maybe zero in legacy DB */ mc->mc_db->md_mod_txnid &&
                         !(*mc->mc_dbistate & DBI_DIRTY))
                            ? mc->mc_db->md_mod_txnid
                            : mc->mc_txn->mt_txnid)) != 0))
        return rc;
    }
  
    mc->mc_snum = 1;
    mc->mc_top = 0;
  
    mdbx_debug("db %d root page %" PRIaPGNO " has flags 0x%X", DDBI(mc), root,
               mc->mc_pg[0]->mp_flags);
  
    if (flags & MDBX_PS_MODIFY) {
      if (unlikely(rc = mdbx_page_touch(mc)))
        return rc;
    }
  
    if (flags & MDBX_PS_ROOTONLY)
      return MDBX_SUCCESS;
  
    return mdbx_page_search_root(mc, key, flags);
  }
  
  /* Return the data associated with a given node.
   *
   * [in] mc      The cursor for this operation.
   * [in] leaf    The node being read.
   * [out] data   Updated to point to the node's data.
   *
   * Returns 0 on success, non-zero on failure. */
  static __always_inline int mdbx_node_read(MDBX_cursor *mc, MDBX_node *node,
                                            MDBX_val *data,
                                            const txnid_t pp_txnid) {
    data->iov_len = node_ds(node);
    data->iov_base = node_data(node);
    if (unlikely(F_ISSET(node_flags(node), F_BIGDATA))) {
      /* Read overflow data. */
      MDBX_page *omp; /* overflow page */
      int rc = mdbx_page_get(mc, node_largedata_pgno(node), &omp, NULL, pp_txnid);
      if (unlikely((rc != MDBX_SUCCESS))) {
        mdbx_debug("read overflow page %" PRIaPGNO " failed",
                   node_largedata_pgno(node));
        return rc;
      }
      data->iov_base = page_data(omp);
    }
    return MDBX_SUCCESS;
  }
  
  int mdbx_get(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key, MDBX_val *data) {
    DKBUF;
    mdbx_debug("===> get db %u key [%s]", dbi, DKEY(key));
  
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!key || !data))
      return MDBX_EINVAL;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    MDBX_cursor_couple cx;
    rc = mdbx_cursor_init(&cx.outer, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    int exact = 0;
    return mdbx_cursor_set(&cx.outer, (MDBX_val *)key, data, MDBX_SET, &exact);
  }
  
  int mdbx_get_equal_or_great(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key,
                              MDBX_val *data) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!key || !data))
      return MDBX_EINVAL;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    if (unlikely(txn->mt_flags & MDBX_TXN_BLOCKED))
      return MDBX_BAD_TXN;
  
    MDBX_cursor_couple cx;
    rc = mdbx_cursor_init(&cx.outer, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    return mdbx_cursor_get(&cx.outer, key, data, MDBX_SET_LOWERBOUND);
  }
  
  int mdbx_get_ex(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
                  size_t *values_count) {
    DKBUF;
    mdbx_debug("===> get db %u key [%s]", dbi, DKEY(key));
  
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!key || !data))
      return MDBX_EINVAL;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    MDBX_cursor_couple cx;
    rc = mdbx_cursor_init(&cx.outer, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    int exact = 0;
    rc = mdbx_cursor_set(&cx.outer, key, data, MDBX_SET_KEY, &exact);
    if (unlikely(rc != MDBX_SUCCESS)) {
      if (rc == MDBX_NOTFOUND && values_count)
        *values_count = 0;
      return rc;
    }
  
    if (values_count) {
      *values_count = 1;
      if (cx.outer.mc_xcursor != NULL) {
        MDBX_node *node = page_node(cx.outer.mc_pg[cx.outer.mc_top],
                                    cx.outer.mc_ki[cx.outer.mc_top]);
        if (F_ISSET(node_flags(node), F_DUPDATA)) {
          mdbx_tassert(txn, cx.outer.mc_xcursor == &cx.inner &&
                                (cx.inner.mx_cursor.mc_flags & C_INITIALIZED));
          *values_count =
              (sizeof(*values_count) >= sizeof(cx.inner.mx_db.md_entries) ||
               cx.inner.mx_db.md_entries <= PTRDIFF_MAX)
                  ? (size_t)cx.inner.mx_db.md_entries
                  : PTRDIFF_MAX;
        }
      }
    }
    return MDBX_SUCCESS;
  }
  
  /* Find a sibling for a page.
   * Replaces the page at the top of the cursor's stack with the specified
   * sibling, if one exists.
   *
   * [in] mc    The cursor for this operation.
   * [in] dir   SIBLING_LEFT or SIBLING_RIGHT.
   *
   * Returns 0 on success, non-zero on failure. */
  static int mdbx_cursor_sibling(MDBX_cursor *mc, int dir) {
    int rc;
    MDBX_node *node;
    MDBX_page *mp;
    assert(dir == SIBLING_LEFT || dir == SIBLING_RIGHT);
  
    if (unlikely(mc->mc_snum < 2))
      return MDBX_NOTFOUND; /* root has no siblings */
  
    mdbx_cursor_pop(mc);
    mdbx_debug("parent page is page %" PRIaPGNO ", index %u",
               mc->mc_pg[mc->mc_top]->mp_pgno, mc->mc_ki[mc->mc_top]);
  
    if ((dir == SIBLING_RIGHT)
            ? (mc->mc_ki[mc->mc_top] + 1u >= page_numkeys(mc->mc_pg[mc->mc_top]))
            : (mc->mc_ki[mc->mc_top] == 0)) {
      mdbx_debug("no more keys aside, moving to next %s sibling",
                 dir ? "right" : "left");
      if (unlikely((rc = mdbx_cursor_sibling(mc, dir)) != MDBX_SUCCESS)) {
        /* undo cursor_pop before returning */
        mc->mc_top++;
        mc->mc_snum++;
        return rc;
      }
    } else {
      assert((dir - 1) == -1 || (dir - 1) == 1);
      mc->mc_ki[mc->mc_top] += (indx_t)(dir - 1);
      mdbx_debug("just moving to %s index key %u",
                 (dir == SIBLING_RIGHT) ? "right" : "left",
                 mc->mc_ki[mc->mc_top]);
    }
    mdbx_cassert(mc, IS_BRANCH(mc->mc_pg[mc->mc_top]));
  
    node = page_node(mp = mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
    if (unlikely((rc = mdbx_page_get(mc, node_pgno(node), &mp, NULL,
                                     pp_txnid4chk(mp, mc->mc_txn))) != 0)) {
      /* mc will be inconsistent if caller does mc_snum++ as above */
      mc->mc_flags &= ~(C_INITIALIZED | C_EOF);
      return rc;
    }
  
    rc = mdbx_cursor_push(mc, mp);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    mc->mc_ki[mc->mc_top] =
        (indx_t)((dir == SIBLING_LEFT) ? page_numkeys(mp) - 1 : 0);
    return MDBX_SUCCESS;
  }
  
  /* Move the cursor to the next data item. */
  static int mdbx_cursor_next(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                              MDBX_cursor_op op) {
    MDBX_page *mp;
    MDBX_node *node;
    int rc;
  
    if ((mc->mc_flags & C_DEL) && op == MDBX_NEXT_DUP)
      return MDBX_NOTFOUND;
  
    if (!(mc->mc_flags & C_INITIALIZED))
      return mdbx_cursor_first(mc, key, data);
  
    mp = mc->mc_pg[mc->mc_top];
    if (mc->mc_flags & C_EOF) {
      if (mc->mc_ki[mc->mc_top] + 1u >= page_numkeys(mp))
        return MDBX_NOTFOUND;
      mc->mc_flags ^= C_EOF;
    }
  
    if (mc->mc_db->md_flags & MDBX_DUPSORT) {
      node = page_node(mp, mc->mc_ki[mc->mc_top]);
      if (F_ISSET(node_flags(node), F_DUPDATA)) {
        if (op == MDBX_NEXT || op == MDBX_NEXT_DUP) {
          rc =
              mdbx_cursor_next(&mc->mc_xcursor->mx_cursor, data, NULL, MDBX_NEXT);
          if (op != MDBX_NEXT || rc != MDBX_NOTFOUND) {
            if (likely(rc == MDBX_SUCCESS))
              get_key_optional(node, key);
            return rc;
          }
        }
      } else {
        mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);
        if (op == MDBX_NEXT_DUP)
          return MDBX_NOTFOUND;
      }
    }
  
    mdbx_debug("cursor_next: top page is %" PRIaPGNO " in cursor %p", mp->mp_pgno,
               (void *)mc);
    if (mc->mc_flags & C_DEL) {
      mc->mc_flags ^= C_DEL;
      goto skip;
    }
  
    int ki = mc->mc_ki[mc->mc_top];
    mc->mc_ki[mc->mc_top] = (indx_t)++ki;
    const int numkeys = page_numkeys(mp);
    if (unlikely(ki >= numkeys)) {
      mdbx_debug("%s", "=====> move to next sibling page");
      mc->mc_ki[mc->mc_top] = (indx_t)(numkeys - 1);
      if (unlikely((rc = mdbx_cursor_sibling(mc, SIBLING_RIGHT)) !=
                   MDBX_SUCCESS)) {
        mc->mc_flags |= C_EOF;
        return rc;
      }
      mp = mc->mc_pg[mc->mc_top];
      mdbx_debug("next page is %" PRIaPGNO ", key index %u", mp->mp_pgno,
                 mc->mc_ki[mc->mc_top]);
    }
  
  skip:
    mdbx_debug("==> cursor points to page %" PRIaPGNO
               " with %u keys, key index %u",
               mp->mp_pgno, page_numkeys(mp), mc->mc_ki[mc->mc_top]);
  
    if (unlikely(!IS_LEAF(mp)))
      return MDBX_CORRUPTED;
  
    if (IS_LEAF2(mp)) {
      if (likely(key)) {
        key->iov_len = mc->mc_db->md_xsize;
        key->iov_base = page_leaf2key(mp, mc->mc_ki[mc->mc_top], key->iov_len);
      }
      return MDBX_SUCCESS;
    }
  
    node = page_node(mp, mc->mc_ki[mc->mc_top]);
    if (F_ISSET(node_flags(node), F_DUPDATA)) {
      rc = mdbx_xcursor_init1(mc, node, mp);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      rc = mdbx_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    } else if (likely(data)) {
      if (unlikely((rc = mdbx_node_read(mc, node, data,
                                        pp_txnid4chk(mp, mc->mc_txn))) !=
                   MDBX_SUCCESS))
        return rc;
    }
  
    get_key_optional(node, key);
    return MDBX_SUCCESS;
  }
  
  /* Move the cursor to the previous data item. */
  static int mdbx_cursor_prev(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                              MDBX_cursor_op op) {
    MDBX_page *mp;
    MDBX_node *node;
    int rc;
  
    if ((mc->mc_flags & C_DEL) && op == MDBX_PREV_DUP)
      return MDBX_NOTFOUND;
  
    if (!(mc->mc_flags & C_INITIALIZED)) {
      rc = mdbx_cursor_last(mc, key, data);
      if (unlikely(rc))
        return rc;
      mc->mc_ki[mc->mc_top]++;
    }
  
    mp = mc->mc_pg[mc->mc_top];
    if ((mc->mc_db->md_flags & MDBX_DUPSORT) &&
        mc->mc_ki[mc->mc_top] < page_numkeys(mp)) {
      node = page_node(mp, mc->mc_ki[mc->mc_top]);
      if (F_ISSET(node_flags(node), F_DUPDATA)) {
        if (op == MDBX_PREV || op == MDBX_PREV_DUP) {
          rc =
              mdbx_cursor_prev(&mc->mc_xcursor->mx_cursor, data, NULL, MDBX_PREV);
          if (op != MDBX_PREV || rc != MDBX_NOTFOUND) {
            if (likely(rc == MDBX_SUCCESS)) {
              get_key_optional(node, key);
              mc->mc_flags &= ~C_EOF;
            }
            return rc;
          }
        }
      } else {
        mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);
        if (op == MDBX_PREV_DUP)
          return MDBX_NOTFOUND;
      }
    }
  
    mdbx_debug("cursor_prev: top page is %" PRIaPGNO " in cursor %p", mp->mp_pgno,
               (void *)mc);
  
    mc->mc_flags &= ~(C_EOF | C_DEL);
  
    int ki = mc->mc_ki[mc->mc_top];
    mc->mc_ki[mc->mc_top] = (indx_t)--ki;
    if (unlikely(ki < 0)) {
      mc->mc_ki[mc->mc_top] = 0;
      mdbx_debug("%s", "=====> move to prev sibling page");
      if ((rc = mdbx_cursor_sibling(mc, SIBLING_LEFT)) != MDBX_SUCCESS)
        return rc;
      mp = mc->mc_pg[mc->mc_top];
      mdbx_debug("prev page is %" PRIaPGNO ", key index %u", mp->mp_pgno,
                 mc->mc_ki[mc->mc_top]);
    }
    mdbx_debug("==> cursor points to page %" PRIaPGNO
               " with %u keys, key index %u",
               mp->mp_pgno, page_numkeys(mp), mc->mc_ki[mc->mc_top]);
  
    if (unlikely(!IS_LEAF(mp)))
      return MDBX_CORRUPTED;
  
    if (IS_LEAF2(mp)) {
      if (likely(key)) {
        key->iov_len = mc->mc_db->md_xsize;
        key->iov_base = page_leaf2key(mp, mc->mc_ki[mc->mc_top], key->iov_len);
      }
      return MDBX_SUCCESS;
    }
  
    node = page_node(mp, mc->mc_ki[mc->mc_top]);
  
    if (F_ISSET(node_flags(node), F_DUPDATA)) {
      rc = mdbx_xcursor_init1(mc, node, mp);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      rc = mdbx_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    } else if (likely(data)) {
      if (unlikely((rc = mdbx_node_read(mc, node, data,
                                        pp_txnid4chk(mp, mc->mc_txn))) !=
                   MDBX_SUCCESS))
        return rc;
    }
  
    get_key_optional(node, key);
    return MDBX_SUCCESS;
  }
  
  /* Set the cursor on a specific data item. */
  static int mdbx_cursor_set(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                             MDBX_cursor_op op, int *exactp) {
    int rc;
    MDBX_page *mp;
    MDBX_node *node = NULL;
    int stub_exactp;
    DKBUF;
  
    exactp = exactp ? exactp : &stub_exactp;
  
    if (unlikely(key->iov_len < mc->mc_dbx->md_klen_min ||
                 key->iov_len > mc->mc_dbx->md_klen_max)) {
      mdbx_cassert(mc, !"Invalid key-size");
      return MDBX_BAD_VALSIZE;
    }
  
    MDBX_val aligned_key = *key;
    uint64_t aligned_keybytes;
    if (mc->mc_db->md_flags & MDBX_INTEGERKEY) {
      switch (aligned_key.iov_len) {
      default:
        mdbx_cassert(mc, !"key-size is invalid for MDBX_INTEGERKEY");
        return MDBX_BAD_VALSIZE;
      case 4:
        if (unlikely(3 & (uintptr_t)aligned_key.iov_base))
          /* copy instead of return error to avoid break compatibility */
          aligned_key.iov_base =
              memcpy(&aligned_keybytes, aligned_key.iov_base, 4);
        break;
      case 8:
        if (unlikely(7 & (uintptr_t)aligned_key.iov_base))
          /* copy instead of return error to avoid break compatibility */
          aligned_key.iov_base =
              memcpy(&aligned_keybytes, aligned_key.iov_base, 8);
        break;
      }
    }
  
    if (mc->mc_xcursor)
      mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);
  
    /* See if we're already on the right page */
    if (mc->mc_flags & C_INITIALIZED) {
      MDBX_val nodekey;
  
      mdbx_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]));
      mp = mc->mc_pg[mc->mc_top];
      if (unlikely(!page_numkeys(mp))) {
        mc->mc_ki[mc->mc_top] = 0;
        mc->mc_flags |= C_EOF;
        return MDBX_NOTFOUND;
      }
      if (IS_LEAF2(mp)) {
        nodekey.iov_len = mc->mc_db->md_xsize;
        nodekey.iov_base = page_leaf2key(mp, 0, nodekey.iov_len);
      } else {
        node = page_node(mp, 0);
        get_key(node, &nodekey);
      }
      rc = mc->mc_dbx->md_cmp(&aligned_key, &nodekey);
      if (unlikely(rc == 0)) {
        /* Probably happens rarely, but first node on the page
         * was the one we wanted. */
        mc->mc_ki[mc->mc_top] = 0;
        *exactp = 1;
        mdbx_cassert(mc, mc->mc_ki[mc->mc_top] <
                                 page_numkeys(mc->mc_pg[mc->mc_top]) ||
                             (mc->mc_flags & C_EOF));
        goto set1;
      }
      if (rc > 0) {
        const unsigned nkeys = page_numkeys(mp);
        unsigned i;
        if (nkeys > 1) {
          if (IS_LEAF2(mp)) {
            nodekey.iov_base = page_leaf2key(mp, nkeys - 1, nodekey.iov_len);
          } else {
            node = page_node(mp, nkeys - 1);
            get_key(node, &nodekey);
          }
          rc = mc->mc_dbx->md_cmp(&aligned_key, &nodekey);
          if (rc == 0) {
            /* last node was the one we wanted */
            mdbx_cassert(mc, nkeys >= 1 && nkeys <= UINT16_MAX + 1);
            mc->mc_ki[mc->mc_top] = (indx_t)(nkeys - 1);
            *exactp = 1;
            mdbx_cassert(mc, mc->mc_ki[mc->mc_top] <
                                     page_numkeys(mc->mc_pg[mc->mc_top]) ||
                                 (mc->mc_flags & C_EOF));
            goto set1;
          }
          if (rc < 0) {
            if (mc->mc_ki[mc->mc_top] < page_numkeys(mp)) {
              /* This is definitely the right page, skip search_page */
              if (IS_LEAF2(mp)) {
                nodekey.iov_base =
                    page_leaf2key(mp, mc->mc_ki[mc->mc_top], nodekey.iov_len);
              } else {
                node = page_node(mp, mc->mc_ki[mc->mc_top]);
                get_key(node, &nodekey);
              }
              rc = mc->mc_dbx->md_cmp(&aligned_key, &nodekey);
              if (rc == 0) {
                /* current node was the one we wanted */
                *exactp = 1;
                mdbx_cassert(mc, mc->mc_ki[mc->mc_top] <
                                         page_numkeys(mc->mc_pg[mc->mc_top]) ||
                                     (mc->mc_flags & C_EOF));
                goto set1;
              }
            }
            rc = 0;
            mc->mc_flags &= ~C_EOF;
            goto set2;
          }
        }
        /* If any parents have right-sibs, search.
         * Otherwise, there's nothing further. */
        for (i = 0; i < mc->mc_top; i++)
          if (mc->mc_ki[i] < page_numkeys(mc->mc_pg[i]) - 1)
            break;
        if (i == mc->mc_top) {
          /* There are no other pages */
          mdbx_cassert(mc, nkeys <= UINT16_MAX);
          mc->mc_ki[mc->mc_top] = (uint16_t)nkeys;
          mc->mc_flags |= C_EOF;
          return MDBX_NOTFOUND;
        }
      }
      if (!mc->mc_top) {
        /* There are no other pages */
        mc->mc_ki[mc->mc_top] = 0;
        if (op == MDBX_SET_RANGE) {
          rc = 0;
          goto set1;
        } else {
          mdbx_cassert(mc, mc->mc_ki[mc->mc_top] <
                                   page_numkeys(mc->mc_pg[mc->mc_top]) ||
                               (mc->mc_flags & C_EOF));
          return MDBX_NOTFOUND;
        }
      }
    } else {
      mc->mc_pg[0] = 0;
    }
  
    rc = mdbx_page_search(mc, &aligned_key, 0);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    mp = mc->mc_pg[mc->mc_top];
    mdbx_cassert(mc, IS_LEAF(mp));
  
  set2:
    node = mdbx_node_search(mc, &aligned_key, exactp);
    if (!*exactp && op != MDBX_SET_RANGE) {
      /* MDBX_SET specified and not an exact match. */
      if (unlikely(mc->mc_ki[mc->mc_top] >= page_numkeys(mc->mc_pg[mc->mc_top])))
        mc->mc_flags |= C_EOF;
      return MDBX_NOTFOUND;
    }
  
    if (node == NULL) {
      mdbx_debug("%s", "===> inexact leaf not found, goto sibling");
      if (unlikely((rc = mdbx_cursor_sibling(mc, SIBLING_RIGHT)) !=
                   MDBX_SUCCESS)) {
        mc->mc_flags |= C_EOF;
        return rc; /* no entries matched */
      }
      mp = mc->mc_pg[mc->mc_top];
      mdbx_cassert(mc, IS_LEAF(mp));
      if (!IS_LEAF2(mp))
        node = page_node(mp, 0);
    }
    mdbx_cassert(mc,
                 mc->mc_ki[mc->mc_top] < page_numkeys(mc->mc_pg[mc->mc_top]) ||
                     (mc->mc_flags & C_EOF));
  
  set1:
    mc->mc_flags |= C_INITIALIZED;
    mc->mc_flags &= ~C_EOF;
  
    if (IS_LEAF2(mp)) {
      if (op == MDBX_SET_RANGE || op == MDBX_SET_KEY) {
        key->iov_len = mc->mc_db->md_xsize;
        key->iov_base = page_leaf2key(mp, mc->mc_ki[mc->mc_top], key->iov_len);
      }
      return MDBX_SUCCESS;
    }
  
    if (F_ISSET(node_flags(node), F_DUPDATA)) {
      rc = mdbx_xcursor_init1(mc, node, mp);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      if (op == MDBX_SET || op == MDBX_SET_KEY || op == MDBX_SET_RANGE) {
        rc = mdbx_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
      } else {
        rc = mdbx_cursor_set(&mc->mc_xcursor->mx_cursor, data, NULL,
                             MDBX_SET_RANGE, NULL);
      }
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    } else if (likely(data)) {
      if (op == MDBX_GET_BOTH || op == MDBX_GET_BOTH_RANGE) {
        if (unlikely(data->iov_len < mc->mc_dbx->md_vlen_min ||
                     data->iov_len > mc->mc_dbx->md_vlen_max)) {
          mdbx_cassert(mc, !"Invalid data-size");
          return MDBX_BAD_VALSIZE;
        }
        MDBX_val aligned_data = *data;
        uint64_t aligned_databytes;
        if (mc->mc_db->md_flags & MDBX_INTEGERDUP) {
          switch (aligned_data.iov_len) {
          default:
            mdbx_cassert(mc, !"data-size is invalid for MDBX_INTEGERDUP");
            return MDBX_BAD_VALSIZE;
          case 4:
            if (unlikely(3 & (uintptr_t)aligned_data.iov_base))
              /* copy instead of return error to avoid break compatibility */
              aligned_data.iov_base =
                  memcpy(&aligned_databytes, aligned_data.iov_base, 4);
            break;
          case 8:
            if (unlikely(7 & (uintptr_t)aligned_data.iov_base))
              /* copy instead of return error to avoid break compatibility */
              aligned_data.iov_base =
                  memcpy(&aligned_databytes, aligned_data.iov_base, 8);
            break;
          }
        }
        MDBX_val olddata;
        if (unlikely((rc = mdbx_node_read(
                          mc, node, &olddata,
                          pp_txnid4chk(mc->mc_pg[mc->mc_top], mc->mc_txn))) !=
                     MDBX_SUCCESS))
          return rc;
        rc = mc->mc_dbx->md_dcmp(&aligned_data, &olddata);
        if (rc) {
          mdbx_cassert(mc, mc->mc_ki[mc->mc_top] <
                                   page_numkeys(mc->mc_pg[mc->mc_top]) ||
                               (mc->mc_flags & C_EOF));
          if (op != MDBX_GET_BOTH_RANGE || rc > 0)
            return MDBX_NOTFOUND;
          *exactp = 0;
          rc = 0;
        }
        *data = olddata;
      } else if (unlikely((rc = mdbx_node_read(mc, node, data,
                                               pp_txnid4chk(mc->mc_pg[mc->mc_top],
                                                            mc->mc_txn))) !=
                          MDBX_SUCCESS))
        return rc;
    }
  
    /* The key already matches in all other cases */
    if (op == MDBX_SET_RANGE || op == MDBX_SET_KEY)
      get_key_optional(node, key);
  
    mdbx_debug("==> cursor placed on key [%s], data [%s]", DKEY(key), DVAL(data));
    return rc;
  }
  
  /* Move the cursor to the first item in the database. */
  static int mdbx_cursor_first(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data) {
    int rc;
  
    if (mc->mc_xcursor)
      mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);
  
    if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
      rc = mdbx_page_search(mc, NULL, MDBX_PS_FIRST);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  
    if (unlikely(!IS_LEAF(mc->mc_pg[mc->mc_top])))
      return MDBX_CORRUPTED;
  
    mc->mc_flags |= C_INITIALIZED;
    mc->mc_flags &= ~C_EOF;
    mc->mc_ki[mc->mc_top] = 0;
  
    if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
      if (likely(key)) {
        key->iov_len = mc->mc_db->md_xsize;
        key->iov_base = page_leaf2key(mc->mc_pg[mc->mc_top], 0, key->iov_len);
      }
      return MDBX_SUCCESS;
    }
  
    MDBX_node *node = page_node(mc->mc_pg[mc->mc_top], 0);
    if (F_ISSET(node_flags(node), F_DUPDATA)) {
      rc = mdbx_xcursor_init1(mc, node, mc->mc_pg[mc->mc_top]);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      rc = mdbx_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
      if (unlikely(rc))
        return rc;
    } else if (likely(data)) {
      if (unlikely((rc = mdbx_node_read(
                        mc, node, data,
                        pp_txnid4chk(mc->mc_pg[mc->mc_top], mc->mc_txn))) !=
                   MDBX_SUCCESS))
        return rc;
    }
  
    get_key_optional(node, key);
    return MDBX_SUCCESS;
  }
  
  /* Move the cursor to the last item in the database. */
  static int mdbx_cursor_last(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data) {
    int rc;
  
    if (mc->mc_xcursor)
      mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);
  
    if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
      rc = mdbx_page_search(mc, NULL, MDBX_PS_LAST);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  
    if (unlikely(!IS_LEAF(mc->mc_pg[mc->mc_top])))
      return MDBX_CORRUPTED;
  
    mc->mc_ki[mc->mc_top] = (indx_t)page_numkeys(mc->mc_pg[mc->mc_top]) - 1;
    mc->mc_flags |= C_INITIALIZED | C_EOF;
  
    if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
      if (likely(key)) {
        key->iov_len = mc->mc_db->md_xsize;
        key->iov_base = page_leaf2key(mc->mc_pg[mc->mc_top],
                                      mc->mc_ki[mc->mc_top], key->iov_len);
      }
      return MDBX_SUCCESS;
    }
  
    MDBX_node *node = page_node(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
    if (F_ISSET(node_flags(node), F_DUPDATA)) {
      rc = mdbx_xcursor_init1(mc, node, mc->mc_pg[mc->mc_top]);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      rc = mdbx_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
      if (unlikely(rc))
        return rc;
    } else if (likely(data)) {
      if (unlikely((rc = mdbx_node_read(
                        mc, node, data,
                        pp_txnid4chk(mc->mc_pg[mc->mc_top], mc->mc_txn))) !=
                   MDBX_SUCCESS))
        return rc;
    }
  
    get_key_optional(node, key);
    return MDBX_SUCCESS;
  }
  
  int mdbx_cursor_get(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                      MDBX_cursor_op op) {
    if (unlikely(mc == NULL))
      return MDBX_EINVAL;
  
    if (unlikely(mc->mc_signature != MDBX_MC_LIVE))
      return (mc->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                       : MDBX_EBADSIGN;
  
    int rc = check_txn(mc->mc_txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    int exact = 0;
    int (*mfunc)(MDBX_cursor * mc, MDBX_val * key, MDBX_val * data);
    switch (op) {
    case MDBX_GET_CURRENT: {
      if (unlikely(!(mc->mc_flags & C_INITIALIZED)))
        return MDBX_ENODATA;
      MDBX_page *mp = mc->mc_pg[mc->mc_top];
      const unsigned nkeys = page_numkeys(mp);
      if (mc->mc_ki[mc->mc_top] >= nkeys) {
        mdbx_cassert(mc, nkeys <= UINT16_MAX);
        mc->mc_ki[mc->mc_top] = (uint16_t)nkeys;
        mc->mc_flags |= C_EOF;
        return MDBX_NOTFOUND;
      }
      mdbx_cassert(mc, nkeys > 0);
  
      rc = MDBX_SUCCESS;
      if (IS_LEAF2(mp)) {
        key->iov_len = mc->mc_db->md_xsize;
        key->iov_base = page_leaf2key(mp, mc->mc_ki[mc->mc_top], key->iov_len);
      } else {
        MDBX_node *node = page_node(mp, mc->mc_ki[mc->mc_top]);
        get_key_optional(node, key);
        if (data) {
          if (F_ISSET(node_flags(node), F_DUPDATA)) {
            if (unlikely(!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED))) {
              rc = mdbx_xcursor_init1(mc, node, mp);
              if (unlikely(rc != MDBX_SUCCESS))
                return rc;
              rc = mdbx_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
              if (unlikely(rc))
                return rc;
            } else {
              rc = mdbx_cursor_get(&mc->mc_xcursor->mx_cursor, data, NULL,
                                   MDBX_GET_CURRENT);
              if (unlikely(rc))
                return rc;
            }
          } else {
            rc = mdbx_node_read(mc, node, data, pp_txnid4chk(mp, mc->mc_txn));
            if (unlikely(rc))
              return rc;
          }
        }
      }
      break;
    }
    case MDBX_GET_BOTH:
    case MDBX_GET_BOTH_RANGE:
      if (unlikely(data == NULL))
        return MDBX_EINVAL;
      if (unlikely(mc->mc_xcursor == NULL))
        return MDBX_INCOMPATIBLE;
      /* fall through */
      __fallthrough;
    case MDBX_SET:
    case MDBX_SET_KEY:
    case MDBX_SET_RANGE:
      if (unlikely(key == NULL))
        return MDBX_EINVAL;
      rc = mdbx_cursor_set(mc, key, data, op, &exact);
      if (mc->mc_flags & C_INITIALIZED) {
        mdbx_cassert(mc, mc->mc_snum > 0 && mc->mc_top < mc->mc_snum);
        mdbx_cassert(mc, mc->mc_ki[mc->mc_top] <
                                 page_numkeys(mc->mc_pg[mc->mc_top]) ||
                             (mc->mc_flags & C_EOF));
      }
      break;
    case MDBX_GET_MULTIPLE:
      if (unlikely(data == NULL || !(mc->mc_flags & C_INITIALIZED)))
        return MDBX_EINVAL;
      if (unlikely(!(mc->mc_db->md_flags & MDBX_DUPFIXED)))
        return MDBX_INCOMPATIBLE;
      rc = MDBX_SUCCESS;
      if ((mc->mc_xcursor->mx_cursor.mc_flags & (C_INITIALIZED | C_EOF)) !=
          C_INITIALIZED)
        break;
      goto fetchm;
    case MDBX_NEXT_MULTIPLE:
      if (unlikely(data == NULL))
        return MDBX_EINVAL;
      if (unlikely(!(mc->mc_db->md_flags & MDBX_DUPFIXED)))
        return MDBX_INCOMPATIBLE;
      rc = mdbx_cursor_next(mc, key, data, MDBX_NEXT_DUP);
      if (rc == MDBX_SUCCESS) {
        if (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) {
          MDBX_cursor *mx;
        fetchm:
          mx = &mc->mc_xcursor->mx_cursor;
          data->iov_len =
              page_numkeys(mx->mc_pg[mx->mc_top]) * mx->mc_db->md_xsize;
          data->iov_base = page_data(mx->mc_pg[mx->mc_top]);
          mx->mc_ki[mx->mc_top] = (indx_t)page_numkeys(mx->mc_pg[mx->mc_top]) - 1;
        } else {
          rc = MDBX_NOTFOUND;
        }
      }
      break;
    case MDBX_PREV_MULTIPLE:
      if (data == NULL)
        return MDBX_EINVAL;
      if (!(mc->mc_db->md_flags & MDBX_DUPFIXED))
        return MDBX_INCOMPATIBLE;
      rc = MDBX_SUCCESS;
      if (!(mc->mc_flags & C_INITIALIZED))
        rc = mdbx_cursor_last(mc, key, data);
      if (rc == MDBX_SUCCESS) {
        MDBX_cursor *mx = &mc->mc_xcursor->mx_cursor;
        if (mx->mc_flags & C_INITIALIZED) {
          rc = mdbx_cursor_sibling(mx, SIBLING_LEFT);
          if (rc == MDBX_SUCCESS)
            goto fetchm;
        } else {
          rc = MDBX_NOTFOUND;
        }
      }
      break;
    case MDBX_NEXT:
    case MDBX_NEXT_DUP:
    case MDBX_NEXT_NODUP:
      rc = mdbx_cursor_next(mc, key, data, op);
      break;
    case MDBX_PREV:
    case MDBX_PREV_DUP:
    case MDBX_PREV_NODUP:
      rc = mdbx_cursor_prev(mc, key, data, op);
      break;
    case MDBX_FIRST:
      rc = mdbx_cursor_first(mc, key, data);
      break;
    case MDBX_FIRST_DUP:
      mfunc = mdbx_cursor_first;
    mmove:
      if (unlikely(data == NULL || !(mc->mc_flags & C_INITIALIZED)))
        return MDBX_EINVAL;
      if (unlikely(mc->mc_xcursor == NULL))
        return MDBX_INCOMPATIBLE;
      if (mc->mc_ki[mc->mc_top] >= page_numkeys(mc->mc_pg[mc->mc_top])) {
        mc->mc_ki[mc->mc_top] = (indx_t)page_numkeys(mc->mc_pg[mc->mc_top]);
        mc->mc_flags |= C_EOF;
        return MDBX_NOTFOUND;
      }
      {
        MDBX_node *node = page_node(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
        if (!F_ISSET(node_flags(node), F_DUPDATA)) {
          get_key_optional(node, key);
          rc = mdbx_node_read(mc, node, data,
                              pp_txnid4chk(mc->mc_pg[mc->mc_top], mc->mc_txn));
          break;
        }
      }
      if (unlikely(!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)))
        return MDBX_EINVAL;
      rc = mfunc(&mc->mc_xcursor->mx_cursor, data, NULL);
      break;
    case MDBX_LAST:
      rc = mdbx_cursor_last(mc, key, data);
      break;
    case MDBX_LAST_DUP:
      mfunc = mdbx_cursor_last;
      goto mmove;
    case MDBX_SET_LOWERBOUND: {
      if (unlikely(key == NULL || data == NULL))
        return MDBX_EINVAL;
      MDBX_val save_data = *data;
      rc = mdbx_cursor_set(mc, key, data, MDBX_SET_RANGE, &exact);
      if (rc == MDBX_SUCCESS && exact && mc->mc_xcursor) {
        mc->mc_flags &= ~C_DEL;
        if (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) {
          *data = save_data;
          exact = 0;
          rc = mdbx_cursor_set(&mc->mc_xcursor->mx_cursor, data, NULL,
                               MDBX_SET_RANGE, &exact);
          if (rc == MDBX_NOTFOUND) {
            mdbx_cassert(mc, !exact);
            rc = mdbx_cursor_next(mc, key, data, MDBX_NEXT_NODUP);
          }
        } else {
          int cmp = mc->mc_dbx->md_dcmp(&save_data, data);
          exact = (cmp == 0);
          if (cmp > 0)
            rc = mdbx_cursor_next(mc, key, data, MDBX_NEXT_NODUP);
        }
      }
      if (rc == MDBX_SUCCESS && !exact)
        rc = MDBX_RESULT_TRUE;
      break;
    }
    default:
      mdbx_debug("unhandled/unimplemented cursor operation %u", op);
      return MDBX_EINVAL;
    }
  
    mc->mc_flags &= ~C_DEL;
    return rc;
  }
  
  /* Touch all the pages in the cursor stack. Set mc_top.
   * Makes sure all the pages are writable, before attempting a write operation.
   * [in] mc The cursor to operate on. */
  static int mdbx_cursor_touch(MDBX_cursor *mc) {
    int rc = MDBX_SUCCESS;
  
    if (mc->mc_dbi >= CORE_DBS &&
        (*mc->mc_dbistate & (DBI_DIRTY | DBI_DUPDATA)) == 0) {
      mdbx_cassert(mc, (mc->mc_flags & C_RECLAIMING) == 0);
      /* Touch DB record of named DB */
      MDBX_cursor_couple cx;
      if (TXN_DBI_CHANGED(mc->mc_txn, mc->mc_dbi))
        return MDBX_BAD_DBI;
      rc = mdbx_cursor_init(&cx.outer, mc->mc_txn, MAIN_DBI);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      rc = mdbx_page_search(&cx.outer, &mc->mc_dbx->md_name, MDBX_PS_MODIFY);
      if (unlikely(rc))
        return rc;
      *mc->mc_dbistate |= DBI_DIRTY;
      mc->mc_txn->mt_flags |= MDBX_TXN_DIRTY;
    }
    mc->mc_top = 0;
    if (mc->mc_snum) {
      do {
        rc = mdbx_page_touch(mc);
      } while (!rc && ++(mc->mc_top) < mc->mc_snum);
      mc->mc_top = mc->mc_snum - 1;
    }
    return rc;
  }
  
  int mdbx_cursor_put(MDBX_cursor *mc, const MDBX_val *key, MDBX_val *data,
                      unsigned flags) {
    MDBX_env *env;
    MDBX_page *sub_root = NULL;
    MDBX_val xdata, *rdata, dkey, olddata;
    MDBX_db nested_dupdb;
    int rc2;
    DKBUF;
  
    if (unlikely(mc == NULL || key == NULL || data == NULL))
      return MDBX_EINVAL;
  
    if (unlikely(mc->mc_signature != MDBX_MC_LIVE))
      return (mc->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                       : MDBX_EBADSIGN;
  
    int rc = check_txn_rw(mc->mc_txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(TXN_DBI_CHANGED(mc->mc_txn, mc->mc_dbi)))
      return MDBX_BAD_DBI;
  
    mdbx_cassert(mc, cursor_is_tracked(mc));
    env = mc->mc_txn->mt_env;
  
    /* Check this first so counter will always be zero on any early failures. */
    size_t mcount = 0, dcount = 0;
    if (unlikely(flags & MDBX_MULTIPLE)) {
      if (unlikely(flags & MDBX_RESERVE))
        return MDBX_EINVAL;
      if (unlikely(!F_ISSET(mc->mc_db->md_flags, MDBX_DUPFIXED)))
        return MDBX_INCOMPATIBLE;
      dcount = data[1].iov_len;
      if (unlikely(dcount < 2 || data->iov_len == 0))
        return MDBX_BAD_VALSIZE;
      if (unlikely(mc->mc_db->md_xsize != data->iov_len) && mc->mc_db->md_xsize)
        return MDBX_BAD_VALSIZE;
      if (unlikely(dcount >
                   MAX_MAPSIZE / 2 / (BRANCH_NODEMAX(MAX_PAGESIZE) - NODESIZE))) {
        /* checking for multiplication overflow */
        if (unlikely(dcount > MAX_MAPSIZE / 2 / data->iov_len))
          return MDBX_TOO_LARGE;
      }
      data[1].iov_len = 0 /* reset done item counter */;
    }
  
    if (flags & MDBX_RESERVE) {
      if (unlikely(mc->mc_db->md_flags & (MDBX_DUPSORT | MDBX_REVERSEDUP |
                                          MDBX_INTEGERDUP | MDBX_DUPFIXED)))
        return MDBX_INCOMPATIBLE;
      data->iov_base = nullptr;
    }
  
    const unsigned nospill = flags & MDBX_NOSPILL;
    flags -= nospill;
  
    if (unlikely(mc->mc_txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_BLOCKED)))
      return (mc->mc_txn->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EACCESS
                                                      : MDBX_BAD_TXN;
  
    uint64_t aligned_keybytes, aligned_databytes;
    MDBX_val aligned_key, aligned_data;
    if (likely((mc->mc_flags & C_SUB) == 0)) {
      if (unlikely(key->iov_len < mc->mc_dbx->md_klen_min ||
                   key->iov_len > mc->mc_dbx->md_klen_max)) {
        mdbx_cassert(mc, !"Invalid key-size");
        return MDBX_BAD_VALSIZE;
      }
      if (unlikely(data->iov_len < mc->mc_dbx->md_vlen_min ||
                   data->iov_len > mc->mc_dbx->md_vlen_max)) {
        mdbx_cassert(mc, !"Invalid data-size");
        return MDBX_BAD_VALSIZE;
      }
  
      if (mc->mc_db->md_flags & MDBX_INTEGERKEY) {
        switch (key->iov_len) {
        default:
          mdbx_cassert(mc, !"key-size is invalid for MDBX_INTEGERKEY");
          return MDBX_BAD_VALSIZE;
        case 4:
          if (unlikely(3 & (uintptr_t)key->iov_base)) {
            /* copy instead of return error to avoid break compatibility */
            aligned_key.iov_base =
                memcpy(&aligned_keybytes, key->iov_base, aligned_key.iov_len = 4);
            key = &aligned_key;
          }
          break;
        case 8:
          if (unlikely(7 & (uintptr_t)key->iov_base)) {
            /* copy instead of return error to avoid break compatibility */
            aligned_key.iov_base =
                memcpy(&aligned_keybytes, key->iov_base, aligned_key.iov_len = 8);
            key = &aligned_key;
          }
          break;
        }
      }
      if (mc->mc_db->md_flags & MDBX_INTEGERDUP) {
        switch (data->iov_len) {
        default:
          mdbx_cassert(mc, !"data-size is invalid for MDBX_INTEGERKEY");
          return MDBX_BAD_VALSIZE;
        case 4:
          if (unlikely(3 & (uintptr_t)data->iov_base)) {
            if (unlikely(flags & MDBX_MULTIPLE))
              return MDBX_BAD_VALSIZE;
            /* copy instead of return error to avoid break compatibility */
            aligned_data.iov_base = memcpy(&aligned_databytes, data->iov_base,
                                           aligned_data.iov_len = 4);
            data = &aligned_data;
          }
          break;
        case 8:
          if (unlikely(7 & (uintptr_t)data->iov_base)) {
            if (unlikely(flags & MDBX_MULTIPLE))
              return MDBX_BAD_VALSIZE;
            /* copy instead of return error to avoid break compatibility */
            aligned_data.iov_base = memcpy(&aligned_databytes, data->iov_base,
                                           aligned_data.iov_len = 8);
            data = &aligned_data;
          }
          break;
        }
      }
    }
  
    mdbx_debug("==> put db %d key [%s], size %" PRIuPTR
               ", data [%s] size %" PRIuPTR,
               DDBI(mc), DKEY(key), key->iov_len,
               DVAL((flags & MDBX_RESERVE) ? nullptr : data), data->iov_len);
  
    int dupdata_flag = 0;
    if ((flags & MDBX_CURRENT) != 0 && (mc->mc_flags & C_SUB) == 0) {
      if (unlikely(flags & (MDBX_APPEND | MDBX_NOOVERWRITE)))
        return MDBX_EINVAL;
      /* Опция MDBX_CURRENT означает, что запрошено обновление текущей записи,
       * на которой сейчас стоит курсор. Проверяем что переданный ключ совпадает
       * со значением в текущей позиции курсора.
       * Здесь проще вызвать mdbx_cursor_get(), так как для обслуживания таблиц
       * с MDBX_DUPSORT также требуется текущий размер данных. */
      MDBX_val current_key, current_data;
      rc = mdbx_cursor_get(mc, &current_key, &current_data, MDBX_GET_CURRENT);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      if (mc->mc_dbx->md_cmp(key, &current_key) != 0)
        return MDBX_EKEYMISMATCH;
  
      if (unlikely((flags & MDBX_MULTIPLE)))
        goto drop_current;
  
      if (F_ISSET(mc->mc_db->md_flags, MDBX_DUPSORT)) {
        MDBX_node *node = page_node(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
        if (F_ISSET(node_flags(node), F_DUPDATA)) {
          mdbx_cassert(mc,
                       mc->mc_xcursor != NULL &&
                           (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED));
          /* Если за ключом более одного значения, либо если размер данных
           * отличается, то вместо обновления требуется удаление и
           * последующая вставка. */
          if (mc->mc_xcursor->mx_db.md_entries > 1 ||
              current_data.iov_len != data->iov_len) {
          drop_current:
            rc = mdbx_cursor_del(mc, flags & MDBX_ALLDUPS);
            if (unlikely(rc != MDBX_SUCCESS))
              return rc;
            flags -= MDBX_CURRENT;
            goto skip_check_samedata;
          }
        } else if (unlikely(node_size(key, data) >
                            /* See note inside leaf_size() */
                            env->me_branch_nodemax)) {
          rc = mdbx_cursor_del(mc, 0);
          if (unlikely(rc != MDBX_SUCCESS))
            return rc;
          flags -= MDBX_CURRENT;
          goto skip_check_samedata;
        }
      }
      if (!(flags & MDBX_RESERVE) &&
          unlikely(cmp_lenfast(&current_data, data) == 0))
        return MDBX_SUCCESS /* the same data, nothing to update */;
    skip_check_samedata:;
    }
  
    if (mc->mc_db->md_root == P_INVALID) {
      /* new database, cursor has nothing to point to */
      mc->mc_snum = 0;
      mc->mc_top = 0;
      mc->mc_flags &= ~C_INITIALIZED;
      rc = MDBX_NO_ROOT;
    } else if ((flags & MDBX_CURRENT) == 0) {
      int exact = false;
      if ((flags & MDBX_APPEND) && mc->mc_db->md_entries > 0) {
        rc = mdbx_cursor_last(mc, &dkey, &olddata);
        if (likely(rc == MDBX_SUCCESS)) {
          rc = mc->mc_dbx->md_cmp(key, &dkey);
          if (likely(rc > 0)) {
            mc->mc_ki[mc->mc_top]++; /* step forward for appending */
            rc = MDBX_NOTFOUND;
          } else {
            if (unlikely(rc != MDBX_SUCCESS || !(flags & MDBX_APPENDDUP)))
              /* new-key < last-key
               * or new-key == last-key without MDBX_APPENDDUP */
              return MDBX_EKEYMISMATCH;
            exact = true;
          }
        }
      } else {
        rc = mdbx_cursor_set(mc, (MDBX_val *)key, &olddata, MDBX_SET, &exact);
      }
      if (likely(rc == MDBX_SUCCESS)) {
        if (exact) {
          if (unlikely(flags & MDBX_NOOVERWRITE)) {
            mdbx_debug("duplicate key [%s]", DKEY(key));
            *data = olddata;
            return MDBX_KEYEXIST;
          }
          if (unlikely(mc->mc_flags & C_SUB)) {
            /* nested subtree of DUPSORT-database with the same key,
             * nothing to update */
            mdbx_assert(env, data->iov_len == 0 && olddata.iov_len == 0);
            return MDBX_SUCCESS;
          }
          if (unlikely(flags & MDBX_ALLDUPS) && mc->mc_xcursor &&
              (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)) {
            rc = mdbx_cursor_del(mc, MDBX_ALLDUPS);
            if (unlikely(rc != MDBX_SUCCESS))
              return rc;
            flags -= MDBX_ALLDUPS;
            rc = MDBX_NOTFOUND;
            exact = false;
          } else /* checking for early exit without dirtying pages */
              if (!(flags & (MDBX_RESERVE | MDBX_MULTIPLE)) &&
                  unlikely(mc->mc_dbx->md_dcmp(data, &olddata) == 0)) {
            if (!mc->mc_xcursor)
              /* the same data, nothing to update */
              return MDBX_SUCCESS;
            if (flags & MDBX_NODUPDATA)
              return MDBX_KEYEXIST;
            if (flags & MDBX_APPENDDUP)
              return MDBX_EKEYMISMATCH;
            if (likely(unsure_equal(mc->mc_dbx->md_dcmp, data, &olddata)))
              /* data is match exactly byte-to-byte, nothing to update */
              return MDBX_SUCCESS;
            else {
              /* The data has differences, but the user-provided comparator
               * considers them equal. So continue update since called without.
               * Continue to update since was called without MDBX_NODUPDATA. */
            }
          }
        }
      } else if (unlikely(rc != MDBX_NOTFOUND))
        return rc;
    }
  
    mc->mc_flags &= ~C_DEL;
  
    /* Cursor is positioned, check for room in the dirty list */
    if (!nospill) {
      if (unlikely(flags & MDBX_MULTIPLE)) {
        rdata = &xdata;
        xdata.iov_len = data->iov_len * dcount;
      } else {
        rdata = data;
      }
      if (unlikely(rc2 = mdbx_page_spill(mc, key, rdata)))
        return rc2;
    }
  
    if (unlikely(rc == MDBX_NO_ROOT)) {
      MDBX_page *np;
      /* new database, write a root leaf page */
      mdbx_debug("%s", "allocating new root leaf page");
      if (unlikely(rc2 = mdbx_page_new(mc, P_LEAF, 1, &np))) {
        return rc2;
      }
      rc2 = mdbx_cursor_push(mc, np);
      if (unlikely(rc2 != MDBX_SUCCESS))
        return rc2;
      mc->mc_db->md_root = np->mp_pgno;
      mc->mc_db->md_depth++;
      if (mc->mc_db->md_flags & MDBX_INTEGERKEY) {
        assert(key->iov_len >= mc->mc_dbx->md_klen_min &&
               key->iov_len <= mc->mc_dbx->md_klen_max);
        mc->mc_dbx->md_klen_min = mc->mc_dbx->md_klen_max = key->iov_len;
      }
      if (mc->mc_db->md_flags & (MDBX_INTEGERDUP | MDBX_DUPFIXED)) {
        assert(data->iov_len >= mc->mc_dbx->md_vlen_min &&
               data->iov_len <= mc->mc_dbx->md_vlen_max);
        assert(mc->mc_xcursor != NULL);
        mc->mc_db->md_xsize = mc->mc_xcursor->mx_db.md_xsize =
            (unsigned)(mc->mc_dbx->md_vlen_min = mc->mc_dbx->md_vlen_max =
                           mc->mc_xcursor->mx_dbx.md_klen_min =
                               mc->mc_xcursor->mx_dbx.md_klen_max =
                                   data->iov_len);
      }
      *mc->mc_dbistate |= DBI_DIRTY;
      mc->mc_txn->mt_flags |= MDBX_TXN_DIRTY;
      if ((mc->mc_db->md_flags & (MDBX_DUPSORT | MDBX_DUPFIXED)) == MDBX_DUPFIXED)
        np->mp_flags |= P_LEAF2;
      mc->mc_flags |= C_INITIALIZED;
    } else {
      /* make sure all cursor pages are writable */
      rc2 = mdbx_cursor_touch(mc);
      if (unlikely(rc2))
        return rc2;
    }
  
    bool insert_key, insert_data, do_sub = false;
    insert_key = insert_data = (rc != MDBX_SUCCESS);
    uint16_t fp_flags = P_LEAF | P_DIRTY;
    MDBX_page *fp = env->me_pbuf;
    fp->mp_txnid = pp_txnid2chk(mc->mc_txn);
    if (insert_key) {
      /* The key does not exist */
      mdbx_debug("inserting key at index %i", mc->mc_ki[mc->mc_top]);
      if ((mc->mc_db->md_flags & MDBX_DUPSORT) &&
          node_size(key, data) >
              /* See note inside leaf_size() */ env->me_branch_nodemax) {
        /* Too big for a node, insert in sub-DB.  Set up an empty
         * "old sub-page" for prep_subDB to expand to a full page. */
        fp->mp_leaf2_ksize =
            (mc->mc_db->md_flags & MDBX_DUPFIXED) ? (uint16_t)data->iov_len : 0;
        fp->mp_lower = fp->mp_upper = 0;
        olddata.iov_len = PAGEHDRSZ;
        goto prep_subDB;
      }
    } else {
      /* there's only a key anyway, so this is a no-op */
      if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
        char *ptr;
        unsigned ksize = mc->mc_db->md_xsize;
        if (unlikely(key->iov_len != ksize))
          return MDBX_BAD_VALSIZE;
        ptr = page_leaf2key(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], ksize);
        memcpy(ptr, key->iov_base, ksize);
      fix_parent:
        /* if overwriting slot 0 of leaf, need to
         * update branch key if there is a parent page */
        if (mc->mc_top && !mc->mc_ki[mc->mc_top]) {
          unsigned dtop = 1;
          mc->mc_top--;
          /* slot 0 is always an empty key, find real slot */
          while (mc->mc_top && !mc->mc_ki[mc->mc_top]) {
            mc->mc_top--;
            dtop++;
          }
          if (mc->mc_ki[mc->mc_top])
            rc2 = mdbx_update_key(mc, key);
          else
            rc2 = MDBX_SUCCESS;
          mdbx_cassert(mc, mc->mc_top + dtop < UINT16_MAX);
          mc->mc_top += (uint16_t)dtop;
          if (rc2)
            return rc2;
        }
  
        if (mdbx_audit_enabled()) {
          int err = mdbx_cursor_check(mc, 0);
          if (unlikely(err != MDBX_SUCCESS))
            return err;
        }
        return MDBX_SUCCESS;
      }
  
    more:;
      if (mdbx_audit_enabled()) {
        int err = mdbx_cursor_check(mc, 0);
        if (unlikely(err != MDBX_SUCCESS))
          return err;
      }
      MDBX_node *node = page_node(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
  
      /* overflow page overwrites need special handling */
      if (unlikely(F_ISSET(node_flags(node), F_BIGDATA))) {
        int level, ovpages,
            dpages = (node_size(key, data) >
                      /* See note inside leaf_size() */ env->me_branch_nodemax)
                         ? number_of_ovpages(env, data->iov_len)
                         : 0;
  
        const pgno_t pg = node_largedata_pgno(node);
        MDBX_page *omp;
        if (unlikely((rc2 = mdbx_page_get(
                          mc, pg, &omp, &level,
                          pp_txnid4chk(mc->mc_pg[mc->mc_top], mc->mc_txn))) != 0))
          return rc2;
        ovpages = omp->mp_pages;
  
        /* Is the ov page large enough? */
        if (unlikely(mc->mc_flags & C_GCFREEZE)
                ? ovpages >= dpages
                : ovpages ==
                      /* LY: add configurable threshold to keep reserve space */
                      dpages) {
          if (!IS_DIRTY(omp) && (level || (env->me_flags & MDBX_WRITEMAP))) {
            rc2 = mdbx_page_unspill(mc->mc_txn, omp, &omp);
            if (unlikely(rc2))
              return rc2;
            level = 0; /* dirty in this txn or clean */
          }
          /* Is it dirty? */
          if (IS_DIRTY(omp)) {
            mdbx_cassert(mc, omp->mp_txnid > SAFE64_INVALID_THRESHOLD);
            /* yes, overwrite it. Note in this case we don't
             * bother to try shrinking the page if the new data
             * is smaller than the overflow threshold. */
            if (unlikely(level > 1)) {
              /* It is writable only in a parent txn */
              MDBX_page *np = mdbx_page_malloc(mc->mc_txn, ovpages);
              if (unlikely(!np))
                return MDBX_ENOMEM;
              /* Note - this page is already counted in parent's dirtyroom */
              rc2 = mdbx_dpl_append(mc->mc_txn->tw.dirtylist, pg, np);
              if (unlikely(rc2 != MDBX_SUCCESS)) {
                rc = rc2;
                mdbx_dpage_free(env, np, ovpages);
                goto fail;
              }
  
              /* Currently we make the page look as with put() in the
               * parent txn, in case the user peeks at MDBX_RESERVEd
               * or unused parts. Some users treat ovpages specially. */
              const size_t whole = pgno2bytes(env, ovpages);
              /* Skip the part where MDBX will put *data.
               * Copy end of page, adjusting alignment so
               * compiler may copy words instead of bytes. */
              const size_t off =
                  (PAGEHDRSZ + data->iov_len) & -(intptr_t)sizeof(size_t);
              memcpy((size_t *)((char *)np + off), (size_t *)((char *)omp + off),
                     whole - off);
              memcpy(np, omp, PAGEHDRSZ); /* Copy header of page */
              omp = np;
            }
            node_set_ds(node, data->iov_len);
            if (F_ISSET(flags, MDBX_RESERVE))
              data->iov_base = page_data(omp);
            else
              memcpy(page_data(omp), data->iov_base, data->iov_len);
  
            if (mdbx_audit_enabled()) {
              int err = mdbx_cursor_check(mc, 0);
              if (unlikely(err != MDBX_SUCCESS))
                return err;
            }
            return MDBX_SUCCESS;
          }
        }
        if ((rc2 = mdbx_page_retire(mc, omp)) != MDBX_SUCCESS)
          return rc2;
      } else {
        olddata.iov_len = node_ds(node);
        olddata.iov_base = node_data(node);
        mdbx_cassert(mc, (char *)olddata.iov_base + olddata.iov_len <=
                             (char *)(mc->mc_pg[mc->mc_top]) + env->me_psize);
  
        /* DB has dups? */
        if (F_ISSET(mc->mc_db->md_flags, MDBX_DUPSORT)) {
          /* Prepare (sub-)page/sub-DB to accept the new item, if needed.
           * fp: old sub-page or a header faking it.
           * mp: new (sub-)page.  offset: growth in page size.
           * xdata: node data with new page or DB. */
          unsigned i;
          size_t offset = 0;
          MDBX_page *mp = fp = xdata.iov_base = env->me_pbuf;
          mp->mp_pgno = mc->mc_pg[mc->mc_top]->mp_pgno;
  
          /* Was a single item before, must convert now */
          if (!F_ISSET(node_flags(node), F_DUPDATA)) {
  
            /* does data match? */
            const int cmp = mc->mc_dbx->md_dcmp(data, &olddata);
            if ((flags & MDBX_APPENDDUP) && unlikely(cmp <= 0))
              return MDBX_EKEYMISMATCH;
            if (cmp == 0) {
              if (flags & MDBX_NODUPDATA)
                return MDBX_KEYEXIST;
              if (likely(unsure_equal(mc->mc_dbx->md_dcmp, data, &olddata))) {
                /* data is match exactly byte-to-byte, nothing to update */
                if (unlikely(flags & MDBX_MULTIPLE)) {
                  rc = MDBX_SUCCESS;
                  goto continue_multiple;
                }
                return MDBX_SUCCESS;
              } else {
                /* The data has differences, but the user-provided comparator
                 * considers them equal. So continue update since called without.
                 * Continue to update since was called without MDBX_NODUPDATA. */
              }
              mdbx_cassert(
                  mc,
                  node_size(key, data) <=
                      /* See note inside leaf_size() */ env->me_branch_nodemax);
              goto current;
            }
  
            /* Just overwrite the current item */
            if (flags & MDBX_CURRENT) {
              mdbx_cassert(
                  mc,
                  node_size(key, data) <=
                      /* See note inside leaf_size() */ env->me_branch_nodemax);
              goto current;
            }
  
            /* Back up original data item */
            memcpy(dkey.iov_base = fp + 1, olddata.iov_base,
                   dkey.iov_len = olddata.iov_len);
            dupdata_flag = 1;
  
            /* Make sub-page header for the dup items, with dummy body */
            fp->mp_flags = P_LEAF | P_DIRTY | P_SUBP;
            fp->mp_lower = 0;
            xdata.iov_len = PAGEHDRSZ + dkey.iov_len + data->iov_len;
            if (mc->mc_db->md_flags & MDBX_DUPFIXED) {
              fp->mp_flags |= P_LEAF2;
              fp->mp_leaf2_ksize = (uint16_t)data->iov_len;
              xdata.iov_len += 2 * data->iov_len; /* leave space for 2 more */
              mdbx_cassert(mc, xdata.iov_len <= env->me_psize);
            } else {
              xdata.iov_len += 2 * (sizeof(indx_t) + NODESIZE) +
                               (dkey.iov_len & 1) + (data->iov_len & 1);
              mdbx_cassert(mc, xdata.iov_len <= env->me_psize);
            }
            fp->mp_upper = (uint16_t)(xdata.iov_len - PAGEHDRSZ);
            olddata.iov_len = xdata.iov_len; /* pretend olddata is fp */
          } else if (node_flags(node) & F_SUBDATA) {
            /* Data is on sub-DB, just store it */
            flags |= F_DUPDATA | F_SUBDATA;
            goto put_sub;
          } else {
            /* Data is on sub-page */
            fp = olddata.iov_base;
            switch (flags) {
            default:
              if (!(mc->mc_db->md_flags & MDBX_DUPFIXED)) {
                offset = node_size(data, nullptr) + sizeof(indx_t);
                break;
              }
              offset = fp->mp_leaf2_ksize;
              if (page_room(fp) < offset) {
                offset *= 4; /* space for 4 more */
                break;
              }
              /* FALLTHRU: Big enough MDBX_DUPFIXED sub-page */
              __fallthrough;
            case MDBX_CURRENT | MDBX_NODUPDATA:
            case MDBX_CURRENT:
              fp->mp_flags |= P_DIRTY;
              fp->mp_txnid = INVALID_TXNID;
              fp->mp_pgno = mp->mp_pgno;
              mc->mc_xcursor->mx_cursor.mc_pg[0] = fp;
              flags |= F_DUPDATA;
              goto put_sub;
            }
            xdata.iov_len = olddata.iov_len + offset;
          }
  
          fp_flags = fp->mp_flags;
          if (NODESIZE + node_ks(node) + xdata.iov_len >
              /* See note inside leaf_size() */ env->me_branch_nodemax) {
            /* Too big for a sub-page, convert to sub-DB */
            fp_flags &= ~P_SUBP;
          prep_subDB:
            nested_dupdb.md_xsize = 0;
            nested_dupdb.md_flags = flags_db2sub(mc->mc_db->md_flags);
            if (mc->mc_db->md_flags & MDBX_DUPFIXED) {
              fp_flags |= P_LEAF2;
              nested_dupdb.md_xsize = fp->mp_leaf2_ksize;
            }
            nested_dupdb.md_depth = 1;
            nested_dupdb.md_branch_pages = 0;
            nested_dupdb.md_leaf_pages = 1;
            nested_dupdb.md_overflow_pages = 0;
            nested_dupdb.md_entries = page_numkeys(fp);
            xdata.iov_len = sizeof(nested_dupdb);
            xdata.iov_base = &nested_dupdb;
            if ((rc2 = mdbx_page_alloc(mc, 1, &mp, MDBX_ALLOC_ALL)))
              return rc2;
            mc->mc_db->md_leaf_pages += 1;
            mdbx_cassert(mc, env->me_psize > olddata.iov_len);
            offset = env->me_psize - (unsigned)olddata.iov_len;
            flags |= F_DUPDATA | F_SUBDATA;
            nested_dupdb.md_root = mp->mp_pgno;
            nested_dupdb.md_seq = 0;
            nested_dupdb.md_mod_txnid = pp_txnid2chk(mc->mc_txn);
            sub_root = mp;
          }
          if (mp != fp) {
            mp->mp_flags = fp_flags | P_DIRTY;
            mp->mp_txnid = INVALID_TXNID;
            mp->mp_leaf2_ksize = fp->mp_leaf2_ksize;
            mp->mp_lower = fp->mp_lower;
            mdbx_cassert(mc, fp->mp_upper + offset <= UINT16_MAX);
            mp->mp_upper = (indx_t)(fp->mp_upper + offset);
            if (unlikely(fp_flags & P_LEAF2)) {
              memcpy(page_data(mp), page_data(fp),
                     page_numkeys(fp) * fp->mp_leaf2_ksize);
            } else {
              memcpy((char *)mp + mp->mp_upper + PAGEHDRSZ,
                     (char *)fp + fp->mp_upper + PAGEHDRSZ,
                     olddata.iov_len - fp->mp_upper - PAGEHDRSZ);
              memcpy((char *)(&mp->mp_ptrs), (char *)(&fp->mp_ptrs),
                     page_numkeys(fp) * sizeof(mp->mp_ptrs[0]));
              for (i = 0; i < page_numkeys(fp); i++) {
                mdbx_cassert(mc, mp->mp_ptrs[i] + offset <= UINT16_MAX);
                mp->mp_ptrs[i] += (indx_t)offset;
              }
            }
          }
  
          rdata = &xdata;
          flags |= F_DUPDATA;
          do_sub = true;
          if (!insert_key)
            mdbx_node_del(mc, 0);
          goto new_sub;
        }
  
        /* MDBX passes F_SUBDATA in 'flags' to write a DB record */
        if (unlikely((node_flags(node) ^ flags) & F_SUBDATA))
          return MDBX_INCOMPATIBLE;
  
      current:
        if (data->iov_len == olddata.iov_len) {
          mdbx_cassert(mc, EVEN(key->iov_len) == EVEN(node_ks(node)));
          /* same size, just replace it. Note that we could
           * also reuse this node if the new data is smaller,
           * but instead we opt to shrink the node in that case. */
          if (F_ISSET(flags, MDBX_RESERVE))
            data->iov_base = olddata.iov_base;
          else if (!(mc->mc_flags & C_SUB))
            memcpy(olddata.iov_base, data->iov_base, data->iov_len);
          else {
            mdbx_cassert(mc, page_numkeys(mc->mc_pg[mc->mc_top]) == 1);
            mdbx_cassert(mc, PAGETYPE(mc->mc_pg[mc->mc_top]) == P_LEAF);
            mdbx_cassert(mc, node_ds(node) == 0);
            mdbx_cassert(mc, node_flags(node) == 0);
            mdbx_cassert(mc, key->iov_len < UINT16_MAX);
            node_set_ks(node, key->iov_len);
            memcpy(node_key(node), key->iov_base, key->iov_len);
            mdbx_cassert(mc, (char *)node_key(node) + node_ds(node) <
                                 (char *)(mc->mc_pg[mc->mc_top]) + env->me_psize);
            goto fix_parent;
          }
  
          if (mdbx_audit_enabled()) {
            int err = mdbx_cursor_check(mc, 0);
            if (unlikely(err != MDBX_SUCCESS))
              return err;
          }
          return MDBX_SUCCESS;
        }
      }
      mdbx_node_del(mc, 0);
    }
  
    rdata = data;
  
  new_sub:;
    unsigned nflags = flags & NODE_ADD_FLAGS;
    size_t nsize = IS_LEAF2(mc->mc_pg[mc->mc_top]) ? key->iov_len
                                                   : leaf_size(env, key, rdata);
    if (page_room(mc->mc_pg[mc->mc_top]) < nsize) {
      if ((flags & (F_DUPDATA | F_SUBDATA)) == F_DUPDATA)
        nflags &= ~MDBX_APPEND; /* sub-page may need room to grow */
      if (!insert_key)
        nflags |= MDBX_SPLIT_REPLACE;
      rc = mdbx_page_split(mc, key, rdata, P_INVALID, nflags);
      if (rc == MDBX_SUCCESS && mdbx_audit_enabled())
        rc = mdbx_cursor_check(mc, 0);
    } else {
      /* There is room already in this leaf page. */
      if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
        mdbx_cassert(mc, (nflags & (F_BIGDATA | F_SUBDATA | F_DUPDATA)) == 0 &&
                             rdata->iov_len == 0);
        rc = mdbx_node_add_leaf2(mc, mc->mc_ki[mc->mc_top], key);
      } else
        rc = mdbx_node_add_leaf(mc, mc->mc_ki[mc->mc_top], key, rdata, nflags);
      if (likely(rc == 0)) {
        /* Adjust other cursors pointing to mp */
        const MDBX_dbi dbi = mc->mc_dbi;
        const unsigned i = mc->mc_top;
        MDBX_page *const mp = mc->mc_pg[i];
        for (MDBX_cursor *m2 = mc->mc_txn->tw.cursors[dbi]; m2;
             m2 = m2->mc_next) {
          MDBX_cursor *m3 =
              (mc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
          if (m3 == mc || m3->mc_snum < mc->mc_snum || m3->mc_pg[i] != mp)
            continue;
          if (m3->mc_ki[i] >= mc->mc_ki[i])
            m3->mc_ki[i] += insert_key;
          if (XCURSOR_INITED(m3))
            XCURSOR_REFRESH(m3, mp, m3->mc_ki[i]);
        }
      }
    }
  
    if (likely(rc == MDBX_SUCCESS)) {
      /* Now store the actual data in the child DB. Note that we're
       * storing the user data in the keys field, so there are strict
       * size limits on dupdata. The actual data fields of the child
       * DB are all zero size. */
      if (do_sub) {
        int xflags;
        size_t ecount;
      put_sub:
        xdata.iov_len = 0;
        xdata.iov_base = nullptr;
        MDBX_node *node = page_node(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
  #define SHIFT_MDBX_NODUPDATA_TO_MDBX_NOOVERWRITE 1
        STATIC_ASSERT(
            (MDBX_NODUPDATA >> SHIFT_MDBX_NODUPDATA_TO_MDBX_NOOVERWRITE) ==
            MDBX_NOOVERWRITE);
        xflags = MDBX_CURRENT | MDBX_NOSPILL |
                 ((flags & MDBX_NODUPDATA) >>
                  SHIFT_MDBX_NODUPDATA_TO_MDBX_NOOVERWRITE);
        if ((flags & MDBX_CURRENT) == 0) {
          xflags -= MDBX_CURRENT;
          rc2 = mdbx_xcursor_init1(mc, node, mc->mc_pg[mc->mc_top]);
          if (unlikely(rc2 != MDBX_SUCCESS))
            return rc2;
        }
        if (sub_root)
          mc->mc_xcursor->mx_cursor.mc_pg[0] = sub_root;
        /* converted, write the original data first */
        if (dupdata_flag) {
          rc = mdbx_cursor_put(&mc->mc_xcursor->mx_cursor, &dkey, &xdata, xflags);
          if (unlikely(rc))
            goto bad_sub;
          /* we've done our job */
          dkey.iov_len = 0;
        }
        if (!(node_flags(node) & F_SUBDATA) || sub_root) {
          /* Adjust other cursors pointing to mp */
          MDBX_cursor *m2;
          MDBX_xcursor *mx = mc->mc_xcursor;
          unsigned i = mc->mc_top;
          MDBX_page *mp = mc->mc_pg[i];
          const int nkeys = page_numkeys(mp);
  
          for (m2 = mc->mc_txn->tw.cursors[mc->mc_dbi]; m2; m2 = m2->mc_next) {
            if (m2 == mc || m2->mc_snum < mc->mc_snum)
              continue;
            if (!(m2->mc_flags & C_INITIALIZED))
              continue;
            if (m2->mc_pg[i] == mp) {
              if (m2->mc_ki[i] == mc->mc_ki[i]) {
                rc2 = mdbx_xcursor_init2(m2, mx, dupdata_flag);
                if (unlikely(rc2 != MDBX_SUCCESS))
                  return rc2;
              } else if (!insert_key && m2->mc_ki[i] < nkeys) {
                XCURSOR_REFRESH(m2, mp, m2->mc_ki[i]);
              }
            }
          }
        }
        mdbx_cassert(mc, mc->mc_xcursor->mx_db.md_entries < PTRDIFF_MAX);
        ecount = (size_t)mc->mc_xcursor->mx_db.md_entries;
  #define SHIFT_MDBX_APPENDDUP_TO_MDBX_APPEND 1
        STATIC_ASSERT((MDBX_APPENDDUP >> SHIFT_MDBX_APPENDDUP_TO_MDBX_APPEND) ==
                      MDBX_APPEND);
        xflags |= (flags & MDBX_APPENDDUP) >> SHIFT_MDBX_APPENDDUP_TO_MDBX_APPEND;
        rc = mdbx_cursor_put(&mc->mc_xcursor->mx_cursor, data, &xdata, xflags);
        if (flags & F_SUBDATA) {
          void *db = node_data(node);
          mc->mc_xcursor->mx_db.md_mod_txnid = pp_txnid2chk(mc->mc_txn);
          memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDBX_db));
        }
        insert_data = (ecount != (size_t)mc->mc_xcursor->mx_db.md_entries);
      }
      /* Increment count unless we just replaced an existing item. */
      if (insert_data)
        mc->mc_db->md_entries++;
      if (insert_key) {
        /* Invalidate txn if we created an empty sub-DB */
        if (unlikely(rc))
          goto bad_sub;
        /* If we succeeded and the key didn't exist before,
         * make sure the cursor is marked valid. */
        mc->mc_flags |= C_INITIALIZED;
      }
      if (flags & MDBX_MULTIPLE) {
        if (!rc) {
        continue_multiple:
          mcount++;
          /* let caller know how many succeeded, if any */
          data[1].iov_len = mcount;
          if (mcount < dcount) {
            data[0].iov_base = (char *)data[0].iov_base + data[0].iov_len;
            insert_key = insert_data = false;
            goto more;
          }
        }
      }
      if (rc == MDBX_SUCCESS && mdbx_audit_enabled())
        rc = mdbx_cursor_check(mc, 0);
      return rc;
    bad_sub:
      if (unlikely(rc == MDBX_KEYEXIST))
        mdbx_error("unexpected %s", "MDBX_KEYEXIST");
      /* should not happen, we deleted that item */
      rc = MDBX_PROBLEM;
    }
  fail:
    mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
    return rc;
  }
  
  int mdbx_cursor_del(MDBX_cursor *mc, MDBX_put_flags_t flags) {
    if (unlikely(!mc))
      return MDBX_EINVAL;
  
    if (unlikely(mc->mc_signature != MDBX_MC_LIVE))
      return (mc->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                       : MDBX_EBADSIGN;
  
    int rc = check_txn_rw(mc->mc_txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(TXN_DBI_CHANGED(mc->mc_txn, mc->mc_dbi)))
      return MDBX_BAD_DBI;
  
    if (unlikely(!(mc->mc_flags & C_INITIALIZED)))
      return MDBX_ENODATA;
  
    if (unlikely(mc->mc_ki[mc->mc_top] >= page_numkeys(mc->mc_pg[mc->mc_top])))
      return MDBX_NOTFOUND;
  
    if (unlikely(!(flags & MDBX_NOSPILL) &&
                 (rc = mdbx_page_spill(mc, NULL, NULL))))
      return rc;
  
    rc = mdbx_cursor_touch(mc);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    if (unlikely(!IS_LEAF(mp)))
      return MDBX_CORRUPTED;
    if (IS_LEAF2(mp))
      goto del_key;
  
    MDBX_node *node = page_node(mp, mc->mc_ki[mc->mc_top]);
    if (F_ISSET(node_flags(node), F_DUPDATA)) {
      if (flags & (MDBX_ALLDUPS | /* for compatibility */ MDBX_NODUPDATA)) {
        /* mdbx_cursor_del0() will subtract the final entry */
        mc->mc_db->md_entries -= mc->mc_xcursor->mx_db.md_entries - 1;
        mc->mc_xcursor->mx_cursor.mc_flags &= ~C_INITIALIZED;
      } else {
        if (!F_ISSET(node_flags(node), F_SUBDATA))
          mc->mc_xcursor->mx_cursor.mc_pg[0] = node_data(node);
        rc = mdbx_cursor_del(&mc->mc_xcursor->mx_cursor, MDBX_NOSPILL);
        if (unlikely(rc))
          return rc;
        /* If sub-DB still has entries, we're done */
        if (mc->mc_xcursor->mx_db.md_entries) {
          if (node_flags(node) & F_SUBDATA) {
            /* update subDB info */
            void *db = node_data(node);
            mc->mc_xcursor->mx_db.md_mod_txnid = pp_txnid2chk(mc->mc_txn);
            memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDBX_db));
          } else {
            MDBX_cursor *m2;
            /* shrink fake page */
            mdbx_node_shrink(mp, mc->mc_ki[mc->mc_top]);
            node = page_node(mp, mc->mc_ki[mc->mc_top]);
            mc->mc_xcursor->mx_cursor.mc_pg[0] = node_data(node);
            /* fix other sub-DB cursors pointed at fake pages on this page */
            for (m2 = mc->mc_txn->tw.cursors[mc->mc_dbi]; m2; m2 = m2->mc_next) {
              if (m2 == mc || m2->mc_snum < mc->mc_snum)
                continue;
              if (!(m2->mc_flags & C_INITIALIZED))
                continue;
              if (m2->mc_pg[mc->mc_top] == mp) {
                MDBX_node *inner = node;
                if (m2->mc_ki[mc->mc_top] >= page_numkeys(mp))
                  continue;
                if (m2->mc_ki[mc->mc_top] != mc->mc_ki[mc->mc_top]) {
                  inner = page_node(mp, m2->mc_ki[mc->mc_top]);
                  if (node_flags(inner) & F_SUBDATA)
                    continue;
                }
                m2->mc_xcursor->mx_cursor.mc_pg[0] = node_data(inner);
              }
            }
          }
          mc->mc_db->md_entries--;
          mdbx_cassert(mc, mc->mc_db->md_entries > 0 && mc->mc_db->md_depth > 0 &&
                               mc->mc_db->md_root != P_INVALID);
          return rc;
        } else {
          mc->mc_xcursor->mx_cursor.mc_flags &= ~C_INITIALIZED;
        }
        /* otherwise fall thru and delete the sub-DB */
      }
  
      if (node_flags(node) & F_SUBDATA) {
        /* add all the child DB's pages to the free list */
        rc = mdbx_drop0(&mc->mc_xcursor->mx_cursor, 0);
        if (unlikely(rc))
          goto fail;
      }
    }
    /* MDBX passes F_SUBDATA in 'flags' to delete a DB record */
    else if (unlikely((node_flags(node) ^ flags) & F_SUBDATA))
      return MDBX_INCOMPATIBLE;
  
    /* add overflow pages to free list */
    if (F_ISSET(node_flags(node), F_BIGDATA)) {
      MDBX_page *omp;
      if (unlikely((rc = mdbx_page_get(mc, node_largedata_pgno(node), &omp, NULL,
                                       pp_txnid4chk(mp, mc->mc_txn))) ||
                   (rc = mdbx_page_retire(mc, omp))))
        goto fail;
    }
  
  del_key:
    return mdbx_cursor_del0(mc);
  
  fail:
    mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
    return rc;
  }
  
  /* Allocate and initialize new pages for a database.
   * Set MDBX_TXN_ERROR on failure.
   *
   * [in] mc a  cursor on the database being added to.
   * [in] flags flags defining what type of page is being allocated.
   * [in] num   the number of pages to allocate. This is usually 1,
   *            unless allocating overflow pages for a large record.
   * [out] mp   Address of a page, or NULL on failure.
   *
   * Returns 0 on success, non-zero on failure. */
  static int mdbx_page_new(MDBX_cursor *mc, unsigned flags, unsigned num,
                           MDBX_page **mp) {
    MDBX_page *np;
    int rc;
  
    if (unlikely((rc = mdbx_page_alloc(mc, num, &np, MDBX_ALLOC_ALL))))
      return rc;
    *mp = np;
    mdbx_debug("allocated new page #%" PRIaPGNO ", size %u", np->mp_pgno,
               mc->mc_txn->mt_env->me_psize);
    np->mp_flags = (uint16_t)(flags | P_DIRTY);
    np->mp_txnid = INVALID_TXNID;
    np->mp_lower = 0;
    np->mp_upper = (indx_t)(mc->mc_txn->mt_env->me_psize - PAGEHDRSZ);
  
    mc->mc_db->md_branch_pages += IS_BRANCH(np);
    mc->mc_db->md_leaf_pages += IS_LEAF(np);
    if (unlikely(IS_OVERFLOW(np))) {
      mc->mc_db->md_overflow_pages += num;
      np->mp_pages = num;
      mdbx_cassert(mc, !(mc->mc_flags & C_SUB));
    } else if (unlikely(mc->mc_flags & C_SUB)) {
      MDBX_db *outer = mdbx_outer_db(mc);
      outer->md_branch_pages += IS_BRANCH(np);
      outer->md_leaf_pages += IS_LEAF(np);
    }
  
    return MDBX_SUCCESS;
  }
  
  static int __must_check_result mdbx_node_add_leaf2(MDBX_cursor *mc,
                                                     unsigned indx,
                                                     const MDBX_val *key) {
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    DKBUF;
    mdbx_debug("add to leaf2-%spage %" PRIaPGNO " index %i, "
               " key size %" PRIuPTR " [%s]",
               IS_SUBP(mp) ? "sub-" : "", mp->mp_pgno, indx,
               key ? key->iov_len : 0, DKEY(key));
  
    mdbx_cassert(mc, key);
    mdbx_cassert(mc, PAGETYPE(mp) == (P_LEAF | P_LEAF2));
    const unsigned ksize = mc->mc_db->md_xsize;
    mdbx_cassert(mc, ksize == key->iov_len);
    const unsigned nkeys = page_numkeys(mp);
  
    /* Just using these for counting */
    const intptr_t lower = mp->mp_lower + sizeof(indx_t);
    const intptr_t upper = mp->mp_upper - (ksize - sizeof(indx_t));
    if (unlikely(lower > upper)) {
      mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
      return MDBX_PAGE_FULL;
    }
    mp->mp_lower = (indx_t)lower;
    mp->mp_upper = (indx_t)upper;
  
    char *const ptr = page_leaf2key(mp, indx, ksize);
    mdbx_cassert(mc, nkeys >= indx);
    const unsigned diff = nkeys - indx;
    if (likely(diff > 0))
      /* Move higher keys up one slot. */
      memmove(ptr + ksize, ptr, diff * ksize);
    /* insert new key */
    memcpy(ptr, key->iov_base, ksize);
    return MDBX_SUCCESS;
  }
  
  static int __must_check_result mdbx_node_add_branch(MDBX_cursor *mc,
                                                      unsigned indx,
                                                      const MDBX_val *key,
                                                      pgno_t pgno) {
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    DKBUF;
    mdbx_debug("add to branch-%spage %" PRIaPGNO " index %i, node-pgno %" PRIaPGNO
               " key size %" PRIuPTR " [%s]",
               IS_SUBP(mp) ? "sub-" : "", mp->mp_pgno, indx, pgno,
               key ? key->iov_len : 0, DKEY(key));
  
    mdbx_cassert(mc, PAGETYPE(mp) == P_BRANCH);
    STATIC_ASSERT(NODESIZE % 2 == 0);
  
    /* Move higher pointers up one slot. */
    const unsigned nkeys = page_numkeys(mp);
    mdbx_cassert(mc, nkeys >= indx);
    for (unsigned i = nkeys; i > indx; --i)
      mp->mp_ptrs[i] = mp->mp_ptrs[i - 1];
  
    /* Adjust free space offsets. */
    const size_t branch_bytes = branch_size(mc->mc_txn->mt_env, key);
    const intptr_t lower = mp->mp_lower + sizeof(indx_t);
    const intptr_t upper = mp->mp_upper - (branch_bytes - sizeof(indx_t));
    if (unlikely(lower > upper)) {
      mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
      return MDBX_PAGE_FULL;
    }
    mp->mp_lower = (indx_t)lower;
    mp->mp_ptrs[indx] = mp->mp_upper = (indx_t)upper;
  
    /* Write the node data. */
    MDBX_node *node = page_node(mp, indx);
    node_set_pgno(node, pgno);
    node_set_flags(node, 0);
    UNALIGNED_POKE_8(node, MDBX_node, mn_extra, 0);
    node_set_ks(node, 0);
    if (likely(key != NULL)) {
      node_set_ks(node, key->iov_len);
      memcpy(node_key(node), key->iov_base, key->iov_len);
    }
    return MDBX_SUCCESS;
  }
  
  static int __must_check_result mdbx_node_add_leaf(MDBX_cursor *mc,
                                                    unsigned indx,
                                                    const MDBX_val *key,
                                                    MDBX_val *data,
                                                    unsigned flags) {
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    DKBUF;
    mdbx_debug("add to leaf-%spage %" PRIaPGNO " index %i, data size %" PRIuPTR
               " key size %" PRIuPTR " [%s]",
               IS_SUBP(mp) ? "sub-" : "", mp->mp_pgno, indx,
               data ? data->iov_len : 0, key ? key->iov_len : 0, DKEY(key));
    mdbx_cassert(mc, key != NULL && data != NULL);
    mdbx_cassert(mc, PAGETYPE(mp) == P_LEAF);
    MDBX_page *largepage = NULL;
  
    size_t leaf_bytes;
    if (unlikely(flags & F_BIGDATA)) {
      /* Data already on overflow page. */
      STATIC_ASSERT(sizeof(pgno_t) % 2 == 0);
      leaf_bytes = node_size(key, nullptr) + sizeof(pgno_t) + sizeof(indx_t);
    } else if (unlikely(node_size(key, data) >
                        /* See note inside leaf_size() */
                        mc->mc_txn->mt_env->me_branch_nodemax)) {
      /* Put data on overflow page. */
      mdbx_ensure(mc->mc_txn->mt_env,
                  !F_ISSET(mc->mc_db->md_flags, MDBX_DUPSORT));
      if (unlikely(flags & (F_DUPDATA | F_SUBDATA)))
        return MDBX_PROBLEM;
      const pgno_t ovpages = number_of_ovpages(mc->mc_txn->mt_env, data->iov_len);
      int rc = mdbx_page_new(mc, P_OVERFLOW, ovpages, &largepage);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      mdbx_debug("allocated %u overflow page(s) %" PRIaPGNO "for %" PRIuPTR
                 " data bytes",
                 largepage->mp_pages, largepage->mp_pgno, data->iov_len);
      flags |= F_BIGDATA;
      leaf_bytes = node_size(key, nullptr) + sizeof(pgno_t) + sizeof(indx_t);
    } else {
      leaf_bytes = node_size(key, data) + sizeof(indx_t);
    }
    mdbx_cassert(mc, leaf_bytes == leaf_size(mc->mc_txn->mt_env, key, data));
  
    /* Move higher pointers up one slot. */
    const unsigned nkeys = page_numkeys(mp);
    mdbx_cassert(mc, nkeys >= indx);
    for (unsigned i = nkeys; i > indx; --i)
      mp->mp_ptrs[i] = mp->mp_ptrs[i - 1];
  
    /* Adjust free space offsets. */
    const intptr_t lower = mp->mp_lower + sizeof(indx_t);
    const intptr_t upper = mp->mp_upper - (leaf_bytes - sizeof(indx_t));
    if (unlikely(lower > upper)) {
      mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
      return MDBX_PAGE_FULL;
    }
    mp->mp_lower = (indx_t)lower;
    mp->mp_ptrs[indx] = mp->mp_upper = (indx_t)upper;
  
    /* Write the node data. */
    MDBX_node *node = page_node(mp, indx);
    node_set_ks(node, key->iov_len);
    node_set_flags(node, (uint8_t)flags);
    UNALIGNED_POKE_8(node, MDBX_node, mn_extra, 0);
    node_set_ds(node, data->iov_len);
    memcpy(node_key(node), key->iov_base, key->iov_len);
  
    void *nodedata = node_data(node);
    if (likely(largepage == NULL)) {
      if (unlikely(flags & F_BIGDATA))
        memcpy(nodedata, data->iov_base, sizeof(pgno_t));
      else if (unlikely(flags & MDBX_RESERVE))
        data->iov_base = nodedata;
      else if (likely(nodedata != data->iov_base &&
                      data->iov_len /* to avoid UBSAN traps*/ != 0))
        memcpy(nodedata, data->iov_base, data->iov_len);
    } else {
      poke_pgno(nodedata, largepage->mp_pgno);
      nodedata = page_data(largepage);
      if (unlikely(flags & MDBX_RESERVE))
        data->iov_base = nodedata;
      else if (likely(nodedata != data->iov_base &&
                      data->iov_len /* to avoid UBSAN traps*/ != 0))
        memcpy(nodedata, data->iov_base, data->iov_len);
    }
    return MDBX_SUCCESS;
  }
  
  /* Delete the specified node from a page.
   * [in] mc Cursor pointing to the node to delete.
   * [in] ksize The size of a node. Only used if the page is
   * part of a MDBX_DUPFIXED database. */
  static void mdbx_node_del(MDBX_cursor *mc, size_t ksize) {
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    int indx = mc->mc_ki[mc->mc_top];
    int i, j, nkeys, ptr;
    MDBX_node *node;
    char *base;
  
    mdbx_debug("delete node %u on %s page %" PRIaPGNO, indx,
               IS_LEAF(mp) ? "leaf" : "branch", mp->mp_pgno);
    nkeys = page_numkeys(mp);
    mdbx_cassert(mc, indx < nkeys);
  
    if (IS_LEAF2(mp)) {
      mdbx_cassert(mc, ksize >= sizeof(indx_t));
      unsigned diff = nkeys - 1 - indx;
      base = page_leaf2key(mp, indx, ksize);
      if (diff)
        memmove(base, base + ksize, diff * ksize);
      mdbx_cassert(mc, mp->mp_lower >= sizeof(indx_t));
      mp->mp_lower -= sizeof(indx_t);
      mdbx_cassert(mc,
                   (size_t)UINT16_MAX - mp->mp_upper >= ksize - sizeof(indx_t));
      mp->mp_upper += (indx_t)(ksize - sizeof(indx_t));
      return;
    }
  
    node = page_node(mp, indx);
    size_t sz = NODESIZE + node_ks(node);
    if (IS_LEAF(mp)) {
      if (F_ISSET(node_flags(node), F_BIGDATA))
        sz += sizeof(pgno_t);
      else
        sz += node_ds(node);
    }
    sz = EVEN(sz);
  
    ptr = mp->mp_ptrs[indx];
    for (i = j = 0; i < nkeys; i++) {
      if (i != indx) {
        mp->mp_ptrs[j] = mp->mp_ptrs[i];
        if (mp->mp_ptrs[i] < ptr) {
          mdbx_cassert(mc, (size_t)UINT16_MAX - mp->mp_ptrs[j] >= sz);
          mp->mp_ptrs[j] += (indx_t)sz;
        }
        j++;
      }
    }
  
    base = (char *)mp + mp->mp_upper + PAGEHDRSZ;
    memmove(base + sz, base, ptr - mp->mp_upper);
  
    mdbx_cassert(mc, mp->mp_lower >= sizeof(indx_t));
    mp->mp_lower -= sizeof(indx_t);
    mdbx_cassert(mc, (size_t)UINT16_MAX - mp->mp_upper >= sz);
    mp->mp_upper += (indx_t)sz;
  
  #if MDBX_DEBUG > 0
    if (mdbx_audit_enabled()) {
      int page_check_err = mdbx_page_check(mc, mp, C_UPDATING);
      mdbx_cassert(mc, page_check_err == MDBX_SUCCESS);
    }
  #endif
  }
  
  /* Compact the main page after deleting a node on a subpage.
   * [in] mp The main page to operate on.
   * [in] indx The index of the subpage on the main page. */
  static void mdbx_node_shrink(MDBX_page *mp, unsigned indx) {
    MDBX_node *node;
    MDBX_page *sp, *xp;
    char *base;
    size_t nsize, delta, len, ptr;
    int i;
  
    node = page_node(mp, indx);
    sp = (MDBX_page *)node_data(node);
    delta = page_room(sp);
    assert(delta > 0);
  
    /* Prepare to shift upward, set len = length(subpage part to shift) */
    if (IS_LEAF2(sp)) {
      delta &= /* do not make the node uneven-sized */ ~(size_t)1;
      if (unlikely(delta) == 0)
        return;
      nsize = node_ds(node) - delta;
      assert(nsize % 1 == 0);
      len = nsize;
    } else {
      xp = (MDBX_page *)((char *)sp + delta); /* destination subpage */
      for (i = page_numkeys(sp); --i >= 0;) {
        assert(sp->mp_ptrs[i] >= delta);
        xp->mp_ptrs[i] = (indx_t)(sp->mp_ptrs[i] - delta);
      }
      nsize = node_ds(node) - delta;
      len = PAGEHDRSZ;
    }
    sp->mp_upper = sp->mp_lower;
    sp->mp_pgno = mp->mp_pgno;
    node_set_ds(node, nsize);
  
    /* Shift <lower nodes...initial part of subpage> upward */
    base = (char *)mp + mp->mp_upper + PAGEHDRSZ;
    memmove(base + delta, base, (char *)sp + len - base);
  
    ptr = mp->mp_ptrs[indx];
    for (i = page_numkeys(mp); --i >= 0;) {
      if (mp->mp_ptrs[i] <= ptr) {
        assert((size_t)UINT16_MAX - mp->mp_ptrs[i] >= delta);
        mp->mp_ptrs[i] += (indx_t)delta;
      }
    }
    assert((size_t)UINT16_MAX - mp->mp_upper >= delta);
    mp->mp_upper += (indx_t)delta;
  }
  
  /* Initial setup of a sorted-dups cursor.
   *
   * Sorted duplicates are implemented as a sub-database for the given key.
   * The duplicate data items are actually keys of the sub-database.
   * Operations on the duplicate data items are performed using a sub-cursor
   * initialized when the sub-database is first accessed. This function does
   * the preliminary setup of the sub-cursor, filling in the fields that
   * depend only on the parent DB.
   *
   * [in] mc The main cursor whose sorted-dups cursor is to be initialized. */
  static int mdbx_xcursor_init0(MDBX_cursor *mc) {
    MDBX_xcursor *mx = mc->mc_xcursor;
    if (unlikely(mx == nullptr)) {
      mdbx_error("unexpected dupsort-page for non-dupsort db/cursor (dbi %u)",
                 mc->mc_dbi);
      return MDBX_CORRUPTED;
    }
  
    mx->mx_cursor.mc_xcursor = NULL;
    mx->mx_cursor.mc_txn = mc->mc_txn;
    mx->mx_cursor.mc_db = &mx->mx_db;
    mx->mx_cursor.mc_dbx = &mx->mx_dbx;
    mx->mx_cursor.mc_dbi = mc->mc_dbi;
    mx->mx_cursor.mc_dbistate = &mx->mx_dbistate;
    mx->mx_cursor.mc_snum = 0;
    mx->mx_cursor.mc_top = 0;
    mx->mx_cursor.mc_flags = C_SUB | (mc->mc_flags & (C_COPYING | C_SKIPORD));
    mx->mx_dbx.md_name.iov_len = 0;
    mx->mx_dbx.md_name.iov_base = NULL;
    mx->mx_dbx.md_cmp = mc->mc_dbx->md_dcmp;
    mx->mx_dbx.md_dcmp = NULL;
    mx->mx_dbx.md_klen_min = INT_MAX;
    mx->mx_dbx.md_vlen_min = mx->mx_dbx.md_klen_max = mx->mx_dbx.md_vlen_max = 0;
    return MDBX_SUCCESS;
  }
  
  /* Final setup of a sorted-dups cursor.
   * Sets up the fields that depend on the data from the main cursor.
   * [in] mc The main cursor whose sorted-dups cursor is to be initialized.
   * [in] node The data containing the MDBX_db record for the sorted-dup database.
   */
  static int mdbx_xcursor_init1(MDBX_cursor *mc, MDBX_node *node,
                                const MDBX_page *mp) {
    MDBX_xcursor *mx = mc->mc_xcursor;
    if (unlikely(mx == nullptr)) {
      mdbx_error("unexpected dupsort-page for non-dupsort db/cursor (dbi %u)",
                 mc->mc_dbi);
      return MDBX_CORRUPTED;
    }
  
    const uint8_t flags = node_flags(node);
    switch (flags) {
    default:
      mdbx_error("invalid node flags %u", flags);
      return MDBX_CORRUPTED;
    case F_DUPDATA | F_SUBDATA:
      if (unlikely(node_ds(node) != sizeof(MDBX_db))) {
        mdbx_error("invalid nested-db record size %zu", node_ds(node));
        return MDBX_CORRUPTED;
      }
      memcpy(&mx->mx_db, node_data(node), sizeof(MDBX_db));
      const txnid_t pp_txnid = IS_DIRTY(mp) ? mc->mc_txn->mt_txnid : mp->mp_txnid;
      if (unlikely(mx->mx_db.md_mod_txnid > pp_txnid)) {
        mdbx_error("nested-db.md_mod_txnid (%" PRIaTXN ") > page-txnid (%" PRIaTXN
                   ")",
                   mx->mx_db.md_mod_txnid, pp_txnid);
        return MDBX_CORRUPTED;
      }
      mx->mx_cursor.mc_pg[0] = 0;
      mx->mx_cursor.mc_snum = 0;
      mx->mx_cursor.mc_top = 0;
      mx->mx_cursor.mc_flags = C_SUB | (mc->mc_flags & (C_COPYING | C_SKIPORD));
      break;
    case F_DUPDATA:
      if (unlikely(node_ds(node) <= PAGEHDRSZ)) {
        mdbx_error("invalid nested-page size %zu", node_ds(node));
        return MDBX_CORRUPTED;
      }
      MDBX_page *fp = node_data(node);
      mx->mx_db.md_depth = 1;
      mx->mx_db.md_branch_pages = 0;
      mx->mx_db.md_leaf_pages = 1;
      mx->mx_db.md_overflow_pages = 0;
      mx->mx_db.md_entries = page_numkeys(fp);
      mx->mx_db.md_root = fp->mp_pgno;
      mx->mx_db.md_mod_txnid = mp->mp_txnid;
      mx->mx_cursor.mc_snum = 1;
      mx->mx_cursor.mc_top = 0;
      mx->mx_cursor.mc_flags =
          C_INITIALIZED | C_SUB | (mc->mc_flags & (C_COPYING | C_SKIPORD));
      mx->mx_cursor.mc_pg[0] = fp;
      mx->mx_cursor.mc_ki[0] = 0;
      mx->mx_db.md_flags = flags_db2sub(mc->mc_db->md_flags);
      mx->mx_db.md_xsize =
          (mc->mc_db->md_flags & MDBX_DUPFIXED) ? fp->mp_leaf2_ksize : 0;
      break;
    }
  
    if (unlikely(mx->mx_db.md_xsize != mc->mc_db->md_xsize)) {
      if (unlikely(mc->mc_db->md_xsize != 0)) {
        mdbx_error("cursor mismatched nested-db md_xsize %u",
                   mc->mc_db->md_xsize);
        return MDBX_CORRUPTED;
      }
      if (unlikely((mc->mc_db->md_flags & MDBX_DUPFIXED) == 0)) {
        mdbx_error("mismatched nested-db md_flags %u", mc->mc_db->md_flags);
        return MDBX_CORRUPTED;
      }
      if (unlikely(mx->mx_db.md_xsize < mc->mc_dbx->md_vlen_min ||
                   mx->mx_db.md_xsize > mc->mc_dbx->md_vlen_max)) {
        mdbx_error("mismatched nested-db.md_xsize (%u) <> min/max value-length "
                   "(%zu/%zu)",
                   mx->mx_db.md_xsize, mc->mc_dbx->md_vlen_min,
                   mc->mc_dbx->md_vlen_max);
        return MDBX_CORRUPTED;
      }
      mc->mc_db->md_xsize = mx->mx_db.md_xsize;
      mc->mc_dbx->md_vlen_min = mc->mc_dbx->md_vlen_max = mx->mx_db.md_xsize;
    }
    mx->mx_dbx.md_klen_min = mc->mc_dbx->md_vlen_min;
    mx->mx_dbx.md_klen_max = mc->mc_dbx->md_vlen_max;
  
    mdbx_debug("Sub-db -%u root page %" PRIaPGNO, mx->mx_cursor.mc_dbi,
               mx->mx_db.md_root);
    mx->mx_dbistate = DBI_VALID | DBI_USRVALID | DBI_DUPDATA;
    return MDBX_SUCCESS;
  }
  
  /* Fixup a sorted-dups cursor due to underlying update.
   * Sets up some fields that depend on the data from the main cursor.
   * Almost the same as init1, but skips initialization steps if the
   * xcursor had already been used.
   * [in] mc The main cursor whose sorted-dups cursor is to be fixed up.
   * [in] src_mx The xcursor of an up-to-date cursor.
   * [in] new_dupdata True if converting from a non-F_DUPDATA item. */
  static int mdbx_xcursor_init2(MDBX_cursor *mc, MDBX_xcursor *src_mx,
                                bool new_dupdata) {
    MDBX_xcursor *mx = mc->mc_xcursor;
    if (unlikely(mx == nullptr)) {
      mdbx_error("unexpected dupsort-page for non-dupsort db/cursor (dbi %u)",
                 mc->mc_dbi);
      return MDBX_CORRUPTED;
    }
  
    if (new_dupdata) {
      mx->mx_cursor.mc_snum = 1;
      mx->mx_cursor.mc_top = 0;
      mx->mx_cursor.mc_flags |= C_INITIALIZED;
      mx->mx_cursor.mc_ki[0] = 0;
      mx->mx_dbistate = DBI_VALID | DBI_USRVALID | DBI_DUPDATA;
    }
  
    mx->mx_dbx.md_klen_min = src_mx->mx_dbx.md_klen_min;
    mx->mx_dbx.md_klen_max = src_mx->mx_dbx.md_klen_max;
    mx->mx_dbx.md_cmp = src_mx->mx_dbx.md_cmp;
    mx->mx_db = src_mx->mx_db;
    mx->mx_cursor.mc_pg[0] = src_mx->mx_cursor.mc_pg[0];
    if (mx->mx_cursor.mc_flags & C_INITIALIZED) {
      mdbx_debug("Sub-db -%u root page %" PRIaPGNO, mx->mx_cursor.mc_dbi,
                 mx->mx_db.md_root);
    }
    return MDBX_SUCCESS;
  }
  
  static __inline int mdbx_couple_init(MDBX_cursor_couple *couple,
                                       const MDBX_dbi dbi, MDBX_txn *const txn,
                                       MDBX_db *const db, MDBX_dbx *const dbx,
                                       uint8_t *const dbstate) {
    couple->outer.mc_signature = MDBX_MC_LIVE;
    couple->outer.mc_next = NULL;
    couple->outer.mc_backup = NULL;
    couple->outer.mc_dbi = dbi;
    couple->outer.mc_txn = txn;
    couple->outer.mc_db = db;
    couple->outer.mc_dbx = dbx;
    couple->outer.mc_dbistate = dbstate;
    couple->outer.mc_snum = 0;
    couple->outer.mc_top = 0;
    couple->outer.mc_pg[0] = 0;
    couple->outer.mc_flags = 0;
    couple->outer.mc_ki[0] = 0;
    couple->outer.mc_xcursor = NULL;
  
    int rc = MDBX_SUCCESS;
    if (unlikely(*couple->outer.mc_dbistate & DBI_STALE)) {
      rc = mdbx_page_search(&couple->outer, NULL, MDBX_PS_ROOTONLY);
      rc = (rc != MDBX_NOTFOUND) ? rc : MDBX_SUCCESS;
    } else if (unlikely(couple->outer.mc_dbx->md_klen_max == 0)) {
      rc = mdbx_setup_dbx(couple->outer.mc_dbx, couple->outer.mc_db,
                          txn->mt_env->me_psize);
    }
  
    if (couple->outer.mc_db->md_flags & MDBX_DUPSORT) {
      couple->inner.mx_cursor.mc_signature = MDBX_MC_LIVE;
      couple->outer.mc_xcursor = &couple->inner;
      rc = mdbx_xcursor_init0(&couple->outer);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      couple->inner.mx_dbx.md_klen_min = couple->outer.mc_dbx->md_vlen_min;
      couple->inner.mx_dbx.md_klen_max = couple->outer.mc_dbx->md_vlen_max;
    }
    return rc;
  }
  
  /* Initialize a cursor for a given transaction and database. */
  static int mdbx_cursor_init(MDBX_cursor *mc, MDBX_txn *txn, MDBX_dbi dbi) {
    STATIC_ASSERT(offsetof(MDBX_cursor_couple, outer) == 0);
    if (unlikely(TXN_DBI_CHANGED(txn, dbi)))
      return MDBX_BAD_DBI;
  
    return mdbx_couple_init(container_of(mc, MDBX_cursor_couple, outer), dbi, txn,
                            &txn->mt_dbs[dbi], &txn->mt_dbxs[dbi],
                            &txn->mt_dbistate[dbi]);
  }
  
  MDBX_cursor *mdbx_cursor_create(void *context) {
    MDBX_cursor_couple *couple = mdbx_calloc(1, sizeof(MDBX_cursor_couple));
    if (unlikely(!couple))
      return nullptr;
  
    couple->outer.mc_signature = MDBX_MC_READY4CLOSE;
    couple->outer.mc_dbi = UINT_MAX;
    couple->mc_userctx = context;
    return &couple->outer;
  }
  
  int mdbx_cursor_set_userctx(MDBX_cursor *mc, void *ctx) {
    if (unlikely(!mc))
      return MDBX_EINVAL;
  
    if (unlikely(mc->mc_signature != MDBX_MC_READY4CLOSE &&
                 mc->mc_signature != MDBX_MC_LIVE))
      return MDBX_EBADSIGN;
  
    MDBX_cursor_couple *couple = container_of(mc, MDBX_cursor_couple, outer);
    couple->mc_userctx = ctx;
    return MDBX_SUCCESS;
  }
  
  void *mdbx_cursor_get_userctx(const MDBX_cursor *mc) {
    if (unlikely(!mc))
      return nullptr;
  
    if (unlikely(mc->mc_signature != MDBX_MC_READY4CLOSE &&
                 mc->mc_signature != MDBX_MC_LIVE))
      return nullptr;
  
    MDBX_cursor_couple *couple = container_of(mc, MDBX_cursor_couple, outer);
    return couple->mc_userctx;
  }
  
  int mdbx_cursor_bind(MDBX_txn *txn, MDBX_cursor *mc, MDBX_dbi dbi) {
    if (unlikely(!mc))
      return MDBX_EINVAL;
  
    if (unlikely(mc->mc_signature != MDBX_MC_READY4CLOSE &&
                 mc->mc_signature != MDBX_MC_LIVE))
      return MDBX_EBADSIGN;
  
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_VALID)))
      return MDBX_BAD_DBI;
  
    if (unlikely(dbi == FREE_DBI && !F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)))
      return MDBX_EACCESS;
  
    if (unlikely(mc->mc_backup)) /* Cursor from parent transaction */ {
      mdbx_cassert(mc, mc->mc_signature == MDBX_MC_LIVE);
      if (unlikely(mc->mc_dbi != dbi ||
                   /* paranoia */ mc->mc_signature != MDBX_MC_LIVE ||
                   mc->mc_txn != txn))
        return MDBX_EINVAL;
  
      assert(mc->mc_db == &txn->mt_dbs[dbi]);
      assert(mc->mc_dbx == &txn->mt_dbxs[dbi]);
      assert(mc->mc_dbi == dbi);
      assert(mc->mc_dbistate == &txn->mt_dbistate[dbi]);
      return likely(mc->mc_dbi == dbi &&
                    /* paranoia */ mc->mc_signature == MDBX_MC_LIVE &&
                    mc->mc_txn == txn)
                 ? MDBX_SUCCESS
                 : MDBX_EINVAL /* Disallow change DBI in nested transactions */;
    }
  
    if (mc->mc_signature == MDBX_MC_LIVE) {
      if (unlikely(!mc->mc_txn || mc->mc_txn->mt_signature != MDBX_MT_SIGNATURE))
        return MDBX_PROBLEM;
      if (mc->mc_flags & C_UNTRACK) {
        mdbx_cassert(mc, !(mc->mc_txn->mt_flags & MDBX_TXN_RDONLY));
        MDBX_cursor **prev = &mc->mc_txn->tw.cursors[mc->mc_dbi];
        while (*prev && *prev != mc)
          prev = &(*prev)->mc_next;
        mdbx_cassert(mc, *prev == mc);
        *prev = mc->mc_next;
      }
      mc->mc_signature = MDBX_MC_READY4CLOSE;
      mc->mc_flags = 0;
      mc->mc_dbi = UINT_MAX;
      mc->mc_next = NULL;
      mc->mc_db = NULL;
      mc->mc_dbx = NULL;
      mc->mc_dbistate = NULL;
    }
    mdbx_cassert(mc, !(mc->mc_flags & C_UNTRACK));
  
    rc = mdbx_cursor_init(mc, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (!(txn->mt_flags & MDBX_TXN_RDONLY)) {
      mc->mc_next = txn->tw.cursors[dbi];
      txn->tw.cursors[dbi] = mc;
      mc->mc_flags |= C_UNTRACK;
    }
  
    return MDBX_SUCCESS;
  }
  
  int mdbx_cursor_open(MDBX_txn *txn, MDBX_dbi dbi, MDBX_cursor **ret) {
    if (unlikely(!ret))
      return MDBX_EINVAL;
    *ret = NULL;
  
    MDBX_cursor *const mc = mdbx_cursor_create(nullptr);
    if (unlikely(!mc))
      return MDBX_ENOMEM;
  
    int rc = mdbx_cursor_bind(txn, mc, dbi);
    if (unlikely(rc != MDBX_SUCCESS)) {
      mdbx_cursor_close(mc);
      return rc;
    }
  
    *ret = mc;
    return MDBX_SUCCESS;
  }
  
  int mdbx_cursor_renew(MDBX_txn *txn, MDBX_cursor *mc) {
    return likely(mc) ? mdbx_cursor_bind(txn, mc, mc->mc_dbi) : MDBX_EINVAL;
  }
  
  int mdbx_cursor_copy(const MDBX_cursor *src, MDBX_cursor *dest) {
    if (unlikely(!src))
      return MDBX_EINVAL;
    if (unlikely(src->mc_signature != MDBX_MC_LIVE))
      return (src->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                        : MDBX_EBADSIGN;
  
    int rc = mdbx_cursor_bind(src->mc_txn, dest, src->mc_dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    assert(dest->mc_db == src->mc_db);
    assert(dest->mc_dbi == src->mc_dbi);
    assert(dest->mc_dbx == src->mc_dbx);
    assert(dest->mc_dbistate == src->mc_dbistate);
  again:
    assert(dest->mc_txn == src->mc_txn);
    dest->mc_flags ^= (dest->mc_flags ^ src->mc_flags) & ~C_UNTRACK;
    dest->mc_top = src->mc_top;
    dest->mc_snum = src->mc_snum;
    for (unsigned i = 0; i < src->mc_snum; ++i) {
      dest->mc_ki[i] = src->mc_ki[i];
      dest->mc_pg[i] = src->mc_pg[i];
    }
  
    if (src->mc_xcursor) {
      dest->mc_xcursor->mx_db = src->mc_xcursor->mx_db;
      dest->mc_xcursor->mx_dbx = src->mc_xcursor->mx_dbx;
      src = &src->mc_xcursor->mx_cursor;
      dest = &dest->mc_xcursor->mx_cursor;
      goto again;
    }
  
    return MDBX_SUCCESS;
  }
  
  void mdbx_cursor_close(MDBX_cursor *mc) {
    if (likely(mc)) {
      mdbx_ensure(NULL, mc->mc_signature == MDBX_MC_LIVE ||
                            mc->mc_signature == MDBX_MC_READY4CLOSE);
      MDBX_txn *const txn = mc->mc_txn;
      MDBX_env *const env = txn ? txn->mt_env : NULL;
      if (!mc->mc_backup) {
        mc->mc_txn = NULL;
        /* Remove from txn, if tracked.
         * A read-only txn (!C_UNTRACK) may have been freed already,
         * so do not peek inside it.  Only write txns track cursors. */
        if (mc->mc_flags & C_UNTRACK) {
          mdbx_ensure(env, check_txn_rw(txn, 0) == MDBX_SUCCESS);
          MDBX_cursor **prev = &txn->tw.cursors[mc->mc_dbi];
          while (*prev && *prev != mc)
            prev = &(*prev)->mc_next;
          mdbx_cassert(mc, *prev == mc);
          *prev = mc->mc_next;
        }
        mc->mc_signature = 0;
        mc->mc_next = mc;
        mdbx_free(mc);
      } else {
        /* Cursor closed before nested txn ends */
        mdbx_cassert(mc, mc->mc_signature == MDBX_MC_LIVE);
        mdbx_ensure(env, check_txn_rw(txn, 0) == MDBX_SUCCESS);
        mc->mc_signature = MDBX_MC_WAIT4EOT;
      }
    }
  }
  
  MDBX_txn *mdbx_cursor_txn(const MDBX_cursor *mc) {
    if (unlikely(!mc || mc->mc_signature != MDBX_MC_LIVE))
      return NULL;
    MDBX_txn *txn = mc->mc_txn;
    if (unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE))
      return NULL;
    if (unlikely(txn->mt_flags & MDBX_TXN_FINISHED))
      return NULL;
    return txn;
  }
  
  MDBX_dbi mdbx_cursor_dbi(const MDBX_cursor *mc) {
    if (unlikely(!mc || mc->mc_signature != MDBX_MC_LIVE))
      return UINT_MAX;
    return mc->mc_dbi;
  }
  
  /* Return the count of duplicate data items for the current key */
  int mdbx_cursor_count(const MDBX_cursor *mc, size_t *countp) {
    if (unlikely(mc == NULL))
      return MDBX_EINVAL;
  
    if (unlikely(mc->mc_signature != MDBX_MC_LIVE))
      return (mc->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                       : MDBX_EBADSIGN;
  
    int rc = check_txn(mc->mc_txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(countp == NULL || !(mc->mc_flags & C_INITIALIZED)))
      return MDBX_EINVAL;
  
    if (!mc->mc_snum) {
      *countp = 0;
      return MDBX_NOTFOUND;
    }
  
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    if ((mc->mc_flags & C_EOF) && mc->mc_ki[mc->mc_top] >= page_numkeys(mp)) {
      *countp = 0;
      return MDBX_NOTFOUND;
    }
  
    *countp = 1;
    if (mc->mc_xcursor != NULL) {
      MDBX_node *node = page_node(mp, mc->mc_ki[mc->mc_top]);
      if (F_ISSET(node_flags(node), F_DUPDATA)) {
        mdbx_cassert(mc, mc->mc_xcursor && (mc->mc_xcursor->mx_cursor.mc_flags &
                                            C_INITIALIZED));
        *countp = unlikely(mc->mc_xcursor->mx_db.md_entries > PTRDIFF_MAX)
                      ? PTRDIFF_MAX
                      : (size_t)mc->mc_xcursor->mx_db.md_entries;
      }
    }
    return MDBX_SUCCESS;
  }
  
  /* Replace the key for a branch node with a new key.
   * Set MDBX_TXN_ERROR on failure.
   * [in] mc Cursor pointing to the node to operate on.
   * [in] key The new key to use.
   * Returns 0 on success, non-zero on failure. */
  static int mdbx_update_key(MDBX_cursor *mc, const MDBX_val *key) {
    MDBX_page *mp;
    MDBX_node *node;
    char *base;
    size_t len;
    int delta, ksize, oksize;
    int ptr, i, nkeys, indx;
    DKBUF;
  
    mdbx_cassert(mc, cursor_is_tracked(mc));
    indx = mc->mc_ki[mc->mc_top];
    mp = mc->mc_pg[mc->mc_top];
    node = page_node(mp, indx);
    ptr = mp->mp_ptrs[indx];
    if (MDBX_DEBUG) {
      MDBX_val k2;
      char kbuf2[DKBUF_MAXKEYSIZE * 2 + 1];
      k2.iov_base = node_key(node);
      k2.iov_len = node_ks(node);
      mdbx_debug("update key %u (offset %u) [%s] to [%s] on page %" PRIaPGNO,
                 indx, ptr, mdbx_dump_val(&k2, kbuf2, sizeof(kbuf2)), DKEY(key),
                 mp->mp_pgno);
    }
  
    /* Sizes must be 2-byte aligned. */
    ksize = EVEN(key->iov_len);
    oksize = EVEN(node_ks(node));
    delta = ksize - oksize;
  
    /* Shift node contents if EVEN(key length) changed. */
    if (delta) {
      if (delta > (int)page_room(mp)) {
        /* not enough space left, do a delete and split */
        mdbx_debug("Not enough room, delta = %d, splitting...", delta);
        pgno_t pgno = node_pgno(node);
        mdbx_node_del(mc, 0);
        int rc = mdbx_page_split(mc, key, NULL, pgno, MDBX_SPLIT_REPLACE);
        if (rc == MDBX_SUCCESS && mdbx_audit_enabled())
          rc = mdbx_cursor_check(mc, C_UPDATING);
        return rc;
      }
  
      nkeys = page_numkeys(mp);
      for (i = 0; i < nkeys; i++) {
        if (mp->mp_ptrs[i] <= ptr) {
          mdbx_cassert(mc, mp->mp_ptrs[i] >= delta);
          mp->mp_ptrs[i] -= (indx_t)delta;
        }
      }
  
      base = (char *)mp + mp->mp_upper + PAGEHDRSZ;
      len = ptr - mp->mp_upper + NODESIZE;
      memmove(base - delta, base, len);
      mdbx_cassert(mc, mp->mp_upper >= delta);
      mp->mp_upper -= (indx_t)delta;
  
      node = page_node(mp, indx);
    }
  
    /* But even if no shift was needed, update ksize */
    node_set_ks(node, key->iov_len);
  
    if (likely(key->iov_len /* to avoid UBSAN traps*/ != 0))
      memcpy(node_key(node), key->iov_base, key->iov_len);
    return MDBX_SUCCESS;
  }
  
  /* Move a node from csrc to cdst. */
  static int mdbx_node_move(MDBX_cursor *csrc, MDBX_cursor *cdst, int fromleft) {
    int rc;
    DKBUF;
  
    MDBX_page *psrc = csrc->mc_pg[csrc->mc_top];
    MDBX_page *pdst = cdst->mc_pg[cdst->mc_top];
    mdbx_cassert(csrc, PAGETYPE(psrc) == PAGETYPE(pdst));
    mdbx_cassert(csrc, csrc->mc_dbi == cdst->mc_dbi);
    mdbx_cassert(csrc, csrc->mc_top == cdst->mc_top);
    if (unlikely(PAGETYPE(psrc) != PAGETYPE(pdst))) {
    bailout:
      csrc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
      return MDBX_PROBLEM;
    }
  
    MDBX_val key4move;
    switch (PAGETYPE(psrc)) {
    case P_BRANCH: {
      const MDBX_node *srcnode = page_node(psrc, csrc->mc_ki[csrc->mc_top]);
      mdbx_cassert(csrc, node_flags(srcnode) == 0);
      const pgno_t srcpg = node_pgno(srcnode);
      key4move.iov_len = node_ks(srcnode);
      key4move.iov_base = node_key(srcnode);
  
      if (csrc->mc_ki[csrc->mc_top] == 0) {
        const unsigned snum = csrc->mc_snum;
        mdbx_cassert(csrc, snum > 0);
        /* must find the lowest key below src */
        rc = mdbx_page_search_lowest(csrc);
        MDBX_page *lowest_page = csrc->mc_pg[csrc->mc_top];
        if (unlikely(rc))
          return rc;
        mdbx_cassert(csrc, IS_LEAF(lowest_page));
        if (unlikely(!IS_LEAF(lowest_page)))
          goto bailout;
        if (IS_LEAF2(lowest_page)) {
          key4move.iov_len = csrc->mc_db->md_xsize;
          key4move.iov_base = page_leaf2key(lowest_page, 0, key4move.iov_len);
        } else {
          const MDBX_node *lowest_node = page_node(lowest_page, 0);
          key4move.iov_len = node_ks(lowest_node);
          key4move.iov_base = node_key(lowest_node);
        }
  
        /* restore cursor after mdbx_page_search_lowest() */
        csrc->mc_snum = snum;
        csrc->mc_top = snum - 1;
        csrc->mc_ki[csrc->mc_top] = 0;
  
        /* paranoia */
        mdbx_cassert(csrc, psrc == csrc->mc_pg[csrc->mc_top]);
        mdbx_cassert(csrc, IS_BRANCH(psrc));
        if (unlikely(!IS_BRANCH(psrc)))
          goto bailout;
      }
  
      if (cdst->mc_ki[cdst->mc_top] == 0) {
        const unsigned snum = cdst->mc_snum;
        mdbx_cassert(csrc, snum > 0);
        MDBX_cursor mn;
        cursor_copy_internal(cdst, &mn);
        mn.mc_xcursor = NULL;
        /* must find the lowest key below dst */
        rc = mdbx_page_search_lowest(&mn);
        if (unlikely(rc))
          return rc;
        MDBX_page *const lowest_page = mn.mc_pg[mn.mc_top];
        mdbx_cassert(cdst, IS_LEAF(lowest_page));
        if (unlikely(!IS_LEAF(lowest_page)))
          goto bailout;
        MDBX_val key;
        if (IS_LEAF2(lowest_page)) {
          key.iov_len = mn.mc_db->md_xsize;
          key.iov_base = page_leaf2key(lowest_page, 0, key.iov_len);
        } else {
          MDBX_node *lowest_node = page_node(lowest_page, 0);
          key.iov_len = node_ks(lowest_node);
          key.iov_base = node_key(lowest_node);
        }
  
        /* restore cursor after mdbx_page_search_lowest() */
        mn.mc_snum = snum;
        mn.mc_top = snum - 1;
        mn.mc_ki[mn.mc_top] = 0;
  
        const intptr_t delta =
            EVEN(key.iov_len) - EVEN(node_ks(page_node(mn.mc_pg[mn.mc_top], 0)));
        const intptr_t needed =
            branch_size(cdst->mc_txn->mt_env, &key4move) + delta;
        const intptr_t have = page_room(pdst);
        if (unlikely(needed > have))
          return MDBX_RESULT_TRUE;
  
        if (unlikely((rc = mdbx_page_touch(csrc)) ||
                     (rc = mdbx_page_touch(cdst))))
          return rc;
        psrc = csrc->mc_pg[csrc->mc_top];
        pdst = cdst->mc_pg[cdst->mc_top];
  
        WITH_CURSOR_TRACKING(mn, rc = mdbx_update_key(&mn, &key));
        if (unlikely(rc))
          return rc;
      } else {
        const size_t needed = branch_size(cdst->mc_txn->mt_env, &key4move);
        const size_t have = page_room(pdst);
        if (unlikely(needed > have))
          return MDBX_RESULT_TRUE;
  
        if (unlikely((rc = mdbx_page_touch(csrc)) ||
                     (rc = mdbx_page_touch(cdst))))
          return rc;
        psrc = csrc->mc_pg[csrc->mc_top];
        pdst = cdst->mc_pg[cdst->mc_top];
      }
  
      mdbx_debug("moving %s-node %u [%s] on page %" PRIaPGNO
                 " to node %u on page %" PRIaPGNO,
                 "branch", csrc->mc_ki[csrc->mc_top], DKEY(&key4move),
                 psrc->mp_pgno, cdst->mc_ki[cdst->mc_top], pdst->mp_pgno);
      /* Add the node to the destination page. */
      rc =
          mdbx_node_add_branch(cdst, cdst->mc_ki[cdst->mc_top], &key4move, srcpg);
    } break;
  
    case P_LEAF: {
      /* Mark src and dst as dirty. */
      if (unlikely((rc = mdbx_page_touch(csrc)) || (rc = mdbx_page_touch(cdst))))
        return rc;
      psrc = csrc->mc_pg[csrc->mc_top];
      pdst = cdst->mc_pg[cdst->mc_top];
      const MDBX_node *srcnode = page_node(psrc, csrc->mc_ki[csrc->mc_top]);
      MDBX_val data;
      data.iov_len = node_ds(srcnode);
      data.iov_base = node_data(srcnode);
      key4move.iov_len = node_ks(srcnode);
      key4move.iov_base = node_key(srcnode);
      mdbx_debug("moving %s-node %u [%s] on page %" PRIaPGNO
                 " to node %u on page %" PRIaPGNO,
                 "leaf", csrc->mc_ki[csrc->mc_top], DKEY(&key4move),
                 psrc->mp_pgno, cdst->mc_ki[cdst->mc_top], pdst->mp_pgno);
      /* Add the node to the destination page. */
      rc = mdbx_node_add_leaf(cdst, cdst->mc_ki[cdst->mc_top], &key4move, &data,
                              node_flags(srcnode));
    } break;
  
    case P_LEAF | P_LEAF2: {
      /* Mark src and dst as dirty. */
      if (unlikely((rc = mdbx_page_touch(csrc)) || (rc = mdbx_page_touch(cdst))))
        return rc;
      psrc = csrc->mc_pg[csrc->mc_top];
      pdst = cdst->mc_pg[cdst->mc_top];
      key4move.iov_len = csrc->mc_db->md_xsize;
      key4move.iov_base =
          page_leaf2key(psrc, csrc->mc_ki[csrc->mc_top], key4move.iov_len);
      mdbx_debug("moving %s-node %u [%s] on page %" PRIaPGNO
                 " to node %u on page %" PRIaPGNO,
                 "leaf2", csrc->mc_ki[csrc->mc_top], DKEY(&key4move),
                 psrc->mp_pgno, cdst->mc_ki[cdst->mc_top], pdst->mp_pgno);
      /* Add the node to the destination page. */
      rc = mdbx_node_add_leaf2(cdst, cdst->mc_ki[cdst->mc_top], &key4move);
    } break;
  
    default:
      goto bailout;
    }
  
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    /* Delete the node from the source page. */
    mdbx_node_del(csrc, key4move.iov_len);
  
    mdbx_cassert(csrc, psrc == csrc->mc_pg[csrc->mc_top]);
    mdbx_cassert(cdst, pdst == cdst->mc_pg[cdst->mc_top]);
    mdbx_cassert(csrc, PAGETYPE(psrc) == PAGETYPE(pdst));
  
    {
      /* Adjust other cursors pointing to mp */
      MDBX_cursor *m2, *m3;
      const MDBX_dbi dbi = csrc->mc_dbi;
      mdbx_cassert(csrc, csrc->mc_top == cdst->mc_top);
      if (fromleft) {
        /* If we're adding on the left, bump others up */
        for (m2 = csrc->mc_txn->tw.cursors[dbi]; m2; m2 = m2->mc_next) {
          m3 = (csrc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
          if (!(m3->mc_flags & C_INITIALIZED) || m3->mc_top < csrc->mc_top)
            continue;
          if (m3 != cdst && m3->mc_pg[csrc->mc_top] == pdst &&
              m3->mc_ki[csrc->mc_top] >= cdst->mc_ki[csrc->mc_top]) {
            m3->mc_ki[csrc->mc_top]++;
          }
          if (m3 != csrc && m3->mc_pg[csrc->mc_top] == psrc &&
              m3->mc_ki[csrc->mc_top] == csrc->mc_ki[csrc->mc_top]) {
            m3->mc_pg[csrc->mc_top] = pdst;
            m3->mc_ki[csrc->mc_top] = cdst->mc_ki[cdst->mc_top];
            mdbx_cassert(csrc, csrc->mc_top > 0);
            m3->mc_ki[csrc->mc_top - 1]++;
          }
          if (XCURSOR_INITED(m3) && IS_LEAF(psrc))
            XCURSOR_REFRESH(m3, m3->mc_pg[csrc->mc_top], m3->mc_ki[csrc->mc_top]);
        }
      } else {
        /* Adding on the right, bump others down */
        for (m2 = csrc->mc_txn->tw.cursors[dbi]; m2; m2 = m2->mc_next) {
          m3 = (csrc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
          if (m3 == csrc)
            continue;
          if (!(m3->mc_flags & C_INITIALIZED) || m3->mc_top < csrc->mc_top)
            continue;
          if (m3->mc_pg[csrc->mc_top] == psrc) {
            if (!m3->mc_ki[csrc->mc_top]) {
              m3->mc_pg[csrc->mc_top] = pdst;
              m3->mc_ki[csrc->mc_top] = cdst->mc_ki[cdst->mc_top];
              mdbx_cassert(csrc, csrc->mc_top > 0);
              m3->mc_ki[csrc->mc_top - 1]--;
            } else {
              m3->mc_ki[csrc->mc_top]--;
            }
            if (XCURSOR_INITED(m3) && IS_LEAF(psrc))
              XCURSOR_REFRESH(m3, m3->mc_pg[csrc->mc_top],
                              m3->mc_ki[csrc->mc_top]);
          }
        }
      }
    }
  
    /* Update the parent separators. */
    if (csrc->mc_ki[csrc->mc_top] == 0) {
      mdbx_cassert(csrc, csrc->mc_top > 0);
      if (csrc->mc_ki[csrc->mc_top - 1] != 0) {
        MDBX_val key;
        if (IS_LEAF2(psrc)) {
          key.iov_len = psrc->mp_leaf2_ksize;
          key.iov_base = page_leaf2key(psrc, 0, key.iov_len);
        } else {
          MDBX_node *srcnode = page_node(psrc, 0);
          key.iov_len = node_ks(srcnode);
          key.iov_base = node_key(srcnode);
        }
        mdbx_debug("update separator for source page %" PRIaPGNO " to [%s]",
                   psrc->mp_pgno, DKEY(&key));
        MDBX_cursor mn;
        cursor_copy_internal(csrc, &mn);
        mn.mc_xcursor = NULL;
        mdbx_cassert(csrc, mn.mc_snum > 0);
        mn.mc_snum--;
        mn.mc_top--;
        /* We want mdbx_rebalance to find mn when doing fixups */
        WITH_CURSOR_TRACKING(mn, rc = mdbx_update_key(&mn, &key));
        if (unlikely(rc != MDBX_SUCCESS))
          return rc;
      }
      if (IS_BRANCH(psrc)) {
        const MDBX_val nullkey = {0, 0};
        const indx_t ix = csrc->mc_ki[csrc->mc_top];
        csrc->mc_ki[csrc->mc_top] = 0;
        rc = mdbx_update_key(csrc, &nullkey);
        csrc->mc_ki[csrc->mc_top] = ix;
        mdbx_cassert(csrc, rc == MDBX_SUCCESS);
      }
    }
  
    if (cdst->mc_ki[cdst->mc_top] == 0) {
      mdbx_cassert(cdst, cdst->mc_top > 0);
      if (cdst->mc_ki[cdst->mc_top - 1] != 0) {
        MDBX_val key;
        if (IS_LEAF2(pdst)) {
          key.iov_len = pdst->mp_leaf2_ksize;
          key.iov_base = page_leaf2key(pdst, 0, key.iov_len);
        } else {
          MDBX_node *srcnode = page_node(pdst, 0);
          key.iov_len = node_ks(srcnode);
          key.iov_base = node_key(srcnode);
        }
        mdbx_debug("update separator for destination page %" PRIaPGNO " to [%s]",
                   pdst->mp_pgno, DKEY(&key));
        MDBX_cursor mn;
        cursor_copy_internal(cdst, &mn);
        mn.mc_xcursor = NULL;
        mdbx_cassert(cdst, mn.mc_snum > 0);
        mn.mc_snum--;
        mn.mc_top--;
        /* We want mdbx_rebalance to find mn when doing fixups */
        WITH_CURSOR_TRACKING(mn, rc = mdbx_update_key(&mn, &key));
        if (unlikely(rc != MDBX_SUCCESS))
          return rc;
      }
      if (IS_BRANCH(pdst)) {
        const MDBX_val nullkey = {0, 0};
        const indx_t ix = cdst->mc_ki[cdst->mc_top];
        cdst->mc_ki[cdst->mc_top] = 0;
        rc = mdbx_update_key(cdst, &nullkey);
        cdst->mc_ki[cdst->mc_top] = ix;
        mdbx_cassert(cdst, rc == MDBX_SUCCESS);
      }
    }
  
    return MDBX_SUCCESS;
  }
  
  /* Merge one page into another.
   *
   * The nodes from the page pointed to by csrc will be copied to the page
   * pointed to by cdst and then the csrc page will be freed.
   *
   * [in] csrc Cursor pointing to the source page.
   * [in] cdst Cursor pointing to the destination page.
   *
   * Returns 0 on success, non-zero on failure. */
  static int mdbx_page_merge(MDBX_cursor *csrc, MDBX_cursor *cdst) {
    MDBX_val key;
    int rc;
  
    mdbx_cassert(csrc, csrc != cdst);
    mdbx_cassert(csrc, cursor_is_tracked(csrc));
    mdbx_cassert(cdst, cursor_is_tracked(cdst));
    const MDBX_page *const psrc = csrc->mc_pg[csrc->mc_top];
    MDBX_page *pdst = cdst->mc_pg[cdst->mc_top];
    mdbx_debug("merging page %" PRIaPGNO " into %" PRIaPGNO, psrc->mp_pgno,
               pdst->mp_pgno);
  
    mdbx_cassert(csrc, PAGETYPE(psrc) == PAGETYPE(pdst));
    mdbx_cassert(csrc,
                 csrc->mc_dbi == cdst->mc_dbi && csrc->mc_db == cdst->mc_db);
    mdbx_cassert(csrc, csrc->mc_snum > 1); /* can't merge root page */
    mdbx_cassert(cdst, cdst->mc_snum > 1);
    mdbx_cassert(cdst, cdst->mc_snum < cdst->mc_db->md_depth ||
                           IS_LEAF(cdst->mc_pg[cdst->mc_db->md_depth - 1]));
    mdbx_cassert(csrc, csrc->mc_snum < csrc->mc_db->md_depth ||
                           IS_LEAF(csrc->mc_pg[csrc->mc_db->md_depth - 1]));
    mdbx_cassert(cdst, page_room(pdst) >= page_used(cdst->mc_txn->mt_env, psrc));
    const int pagetype = PAGETYPE(psrc);
  
    /* Move all nodes from src to dst */
    const unsigned dst_nkeys = page_numkeys(pdst);
    const unsigned src_nkeys = page_numkeys(psrc);
    mdbx_cassert(cdst, dst_nkeys + src_nkeys >=
                           (unsigned)(IS_LEAF(psrc) ? 1 : MDBX_MINKEYS));
    if (likely(src_nkeys)) {
      unsigned j = dst_nkeys;
      if (unlikely(pagetype & P_LEAF2)) {
        /* Mark dst as dirty. */
        if (unlikely(rc = mdbx_page_touch(cdst)))
          return rc;
  
        key.iov_len = csrc->mc_db->md_xsize;
        key.iov_base = page_data(psrc);
        unsigned i = 0;
        do {
          rc = mdbx_node_add_leaf2(cdst, j++, &key);
          if (unlikely(rc != MDBX_SUCCESS))
            return rc;
          key.iov_base = (char *)key.iov_base + key.iov_len;
        } while (++i != src_nkeys);
      } else {
        MDBX_node *srcnode = page_node(psrc, 0);
        key.iov_len = node_ks(srcnode);
        key.iov_base = node_key(srcnode);
        if (pagetype & P_BRANCH) {
          MDBX_cursor mn;
          cursor_copy_internal(csrc, &mn);
          mn.mc_xcursor = NULL;
          /* must find the lowest key below src */
          rc = mdbx_page_search_lowest(&mn);
          if (unlikely(rc))
            return rc;
  
          const MDBX_page *mp = mn.mc_pg[mn.mc_top];
          if (likely(!IS_LEAF2(mp))) {
            mdbx_cassert(&mn, IS_LEAF(mp));
            const MDBX_node *lowest = page_node(mp, 0);
            key.iov_len = node_ks(lowest);
            key.iov_base = node_key(lowest);
          } else {
            mdbx_cassert(&mn, mn.mc_top > csrc->mc_top);
            key.iov_len = mp->mp_leaf2_ksize;
            key.iov_base = page_leaf2key(mp, mn.mc_ki[mn.mc_top], key.iov_len);
          }
          mdbx_cassert(&mn, key.iov_len >= csrc->mc_dbx->md_klen_min);
          mdbx_cassert(&mn, key.iov_len <= csrc->mc_dbx->md_klen_max);
  
          const size_t dst_room = page_room(pdst);
          const size_t src_used = page_used(cdst->mc_txn->mt_env, psrc);
          const size_t space_needed = src_used - node_ks(srcnode) + key.iov_len;
          if (unlikely(space_needed > dst_room))
            return MDBX_RESULT_TRUE;
        }
  
        /* Mark dst as dirty. */
        if (unlikely(rc = mdbx_page_touch(cdst)))
          return rc;
  
        unsigned i = 0;
        while (true) {
          if (pagetype & P_LEAF) {
            MDBX_val data;
            data.iov_len = node_ds(srcnode);
            data.iov_base = node_data(srcnode);
            rc = mdbx_node_add_leaf(cdst, j++, &key, &data, node_flags(srcnode));
          } else {
            mdbx_cassert(csrc, node_flags(srcnode) == 0);
            rc = mdbx_node_add_branch(cdst, j++, &key, node_pgno(srcnode));
          }
          if (unlikely(rc != MDBX_SUCCESS))
            return rc;
  
          if (++i == src_nkeys)
            break;
          srcnode = page_node(psrc, i);
          key.iov_len = node_ks(srcnode);
          key.iov_base = node_key(srcnode);
        }
      }
  
      pdst = cdst->mc_pg[cdst->mc_top];
      mdbx_debug("dst page %" PRIaPGNO " now has %u keys (%.1f%% filled)",
                 pdst->mp_pgno, page_numkeys(pdst),
                 page_fill(cdst->mc_txn->mt_env, pdst));
  
      mdbx_cassert(csrc, psrc == csrc->mc_pg[csrc->mc_top]);
      mdbx_cassert(cdst, pdst == cdst->mc_pg[cdst->mc_top]);
    }
  
    /* Unlink the src page from parent and add to free list. */
    csrc->mc_top--;
    mdbx_node_del(csrc, 0);
    if (csrc->mc_ki[csrc->mc_top] == 0) {
      const MDBX_val nullkey = {0, 0};
      rc = mdbx_update_key(csrc, &nullkey);
      if (unlikely(rc)) {
        csrc->mc_top++;
        return rc;
      }
    }
    csrc->mc_top++;
  
    mdbx_cassert(csrc, psrc == csrc->mc_pg[csrc->mc_top]);
    mdbx_cassert(cdst, pdst == cdst->mc_pg[cdst->mc_top]);
  
    {
      /* Adjust other cursors pointing to mp */
      MDBX_cursor *m2, *m3;
      const MDBX_dbi dbi = csrc->mc_dbi;
      const unsigned top = csrc->mc_top;
  
      for (m2 = csrc->mc_txn->tw.cursors[dbi]; m2; m2 = m2->mc_next) {
        m3 = (csrc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
        if (m3 == csrc || top >= m3->mc_snum)
          continue;
        if (m3->mc_pg[top] == psrc) {
          m3->mc_pg[top] = pdst;
          mdbx_cassert(m3, dst_nkeys + m3->mc_ki[top] <= UINT16_MAX);
          m3->mc_ki[top] += (indx_t)dst_nkeys;
          m3->mc_ki[top - 1] = cdst->mc_ki[top - 1];
        } else if (m3->mc_pg[top - 1] == csrc->mc_pg[top - 1] &&
                   m3->mc_ki[top - 1] > csrc->mc_ki[top - 1]) {
          m3->mc_ki[top - 1]--;
        }
        if (XCURSOR_INITED(m3) && IS_LEAF(psrc))
          XCURSOR_REFRESH(m3, m3->mc_pg[top], m3->mc_ki[top]);
      }
    }
  
    /* If not operating on GC, allow this page to be reused
     * in this txn. Otherwise just add to free list. */
    rc = mdbx_page_retire(csrc, (MDBX_page *)psrc);
    if (unlikely(rc))
      return rc;
  
    mdbx_cassert(cdst, cdst->mc_db->md_entries > 0);
    mdbx_cassert(cdst, cdst->mc_snum <= cdst->mc_db->md_depth);
    mdbx_cassert(cdst, cdst->mc_top > 0);
    mdbx_cassert(cdst, cdst->mc_snum == cdst->mc_top + 1);
    MDBX_page *const top_page = cdst->mc_pg[cdst->mc_top];
    const indx_t top_indx = cdst->mc_ki[cdst->mc_top];
    const unsigned save_snum = cdst->mc_snum;
    const uint16_t save_depth = cdst->mc_db->md_depth;
    mdbx_cursor_pop(cdst);
    rc = mdbx_rebalance(cdst);
    if (unlikely(rc))
      return rc;
  
    mdbx_cassert(cdst, cdst->mc_db->md_entries > 0);
    mdbx_cassert(cdst, cdst->mc_snum <= cdst->mc_db->md_depth);
    mdbx_cassert(cdst, cdst->mc_snum == cdst->mc_top + 1);
  
    if (IS_LEAF(cdst->mc_pg[cdst->mc_top])) {
      /* LY: don't touch cursor if top-page is a LEAF */
      mdbx_cassert(cdst, IS_LEAF(cdst->mc_pg[cdst->mc_top]) ||
                             PAGETYPE(cdst->mc_pg[cdst->mc_top]) == pagetype);
      return MDBX_SUCCESS;
    }
  
    mdbx_cassert(cdst, page_numkeys(top_page) == dst_nkeys + src_nkeys);
  
    if (pagetype != PAGETYPE(top_page)) {
      /* LY: LEAF-page becomes BRANCH, unable restore cursor's stack */
      goto bailout;
    }
  
    if (top_page == cdst->mc_pg[cdst->mc_top]) {
      /* LY: don't touch cursor if prev top-page already on the top */
      mdbx_cassert(cdst, cdst->mc_ki[cdst->mc_top] == top_indx);
      mdbx_cassert(cdst, IS_LEAF(cdst->mc_pg[cdst->mc_top]) ||
                             PAGETYPE(cdst->mc_pg[cdst->mc_top]) == pagetype);
      return MDBX_SUCCESS;
    }
  
    const int new_snum = save_snum - save_depth + cdst->mc_db->md_depth;
    if (unlikely(new_snum < 1 || new_snum > cdst->mc_db->md_depth)) {
      /* LY: out of range, unable restore cursor's stack */
      goto bailout;
    }
  
    if (top_page == cdst->mc_pg[new_snum - 1]) {
      mdbx_cassert(cdst, cdst->mc_ki[new_snum - 1] == top_indx);
      /* LY: restore cursor stack */
      cdst->mc_snum = (uint16_t)new_snum;
      cdst->mc_top = (uint16_t)new_snum - 1;
      mdbx_cassert(cdst, cdst->mc_snum < cdst->mc_db->md_depth ||
                             IS_LEAF(cdst->mc_pg[cdst->mc_db->md_depth - 1]));
      mdbx_cassert(cdst, IS_LEAF(cdst->mc_pg[cdst->mc_top]) ||
                             PAGETYPE(cdst->mc_pg[cdst->mc_top]) == pagetype);
      return MDBX_SUCCESS;
    }
  
    MDBX_page *const stub_page = (MDBX_page *)(~(uintptr_t)top_page);
    const indx_t stub_indx = top_indx;
    if (save_depth > cdst->mc_db->md_depth &&
        ((cdst->mc_pg[save_snum - 1] == top_page &&
          cdst->mc_ki[save_snum - 1] == top_indx) ||
         (cdst->mc_pg[save_snum - 1] == stub_page &&
          cdst->mc_ki[save_snum - 1] == stub_indx))) {
      /* LY: restore cursor stack */
      cdst->mc_pg[new_snum - 1] = top_page;
      cdst->mc_ki[new_snum - 1] = top_indx;
      cdst->mc_pg[new_snum] = (MDBX_page *)(~(uintptr_t)cdst->mc_pg[new_snum]);
      cdst->mc_ki[new_snum] = ~cdst->mc_ki[new_snum];
      cdst->mc_snum = (uint16_t)new_snum;
      cdst->mc_top = (uint16_t)new_snum - 1;
      mdbx_cassert(cdst, cdst->mc_snum < cdst->mc_db->md_depth ||
                             IS_LEAF(cdst->mc_pg[cdst->mc_db->md_depth - 1]));
      mdbx_cassert(cdst, IS_LEAF(cdst->mc_pg[cdst->mc_top]) ||
                             PAGETYPE(cdst->mc_pg[cdst->mc_top]) == pagetype);
      return MDBX_SUCCESS;
    }
  
  bailout:
    /* LY: unable restore cursor's stack */
    cdst->mc_flags &= ~C_INITIALIZED;
    return MDBX_CURSOR_FULL;
  }
  
  /* Copy the contents of a cursor.
   * [in] csrc The cursor to copy from.
   * [out] cdst The cursor to copy to. */
  static void cursor_copy_internal(const MDBX_cursor *csrc, MDBX_cursor *cdst) {
    mdbx_cassert(csrc,
                 csrc->mc_txn->mt_txnid >= *csrc->mc_txn->mt_env->me_oldest);
    cdst->mc_txn = csrc->mc_txn;
    cdst->mc_dbi = csrc->mc_dbi;
    cdst->mc_db = csrc->mc_db;
    cdst->mc_dbx = csrc->mc_dbx;
    cdst->mc_snum = csrc->mc_snum;
    cdst->mc_top = csrc->mc_top;
    cdst->mc_flags = csrc->mc_flags;
  
    for (unsigned i = 0; i < csrc->mc_snum; i++) {
      cdst->mc_pg[i] = csrc->mc_pg[i];
      cdst->mc_ki[i] = csrc->mc_ki[i];
    }
  }
  
  /* Rebalance the tree after a delete operation.
   * [in] mc Cursor pointing to the page where rebalancing should begin.
   * Returns 0 on success, non-zero on failure. */
  static int mdbx_rebalance(MDBX_cursor *mc) {
    mdbx_cassert(mc, cursor_is_tracked(mc));
    mdbx_cassert(mc, mc->mc_snum > 0);
    mdbx_cassert(mc, mc->mc_snum < mc->mc_db->md_depth ||
                         IS_LEAF(mc->mc_pg[mc->mc_db->md_depth - 1]));
    const int pagetype = PAGETYPE(mc->mc_pg[mc->mc_top]);
  
    STATIC_ASSERT(P_BRANCH == 1);
    const unsigned minkeys = (pagetype & P_BRANCH) + 1;
  
    /* The threshold of minimum page fill factor, in form of a negative binary
     * exponent, i.e. X = 2 means 1/(2**X) == 1/(2**2) == 1/4 == 25%.
     * Pages emptier than this are candidates for merging. */
    const unsigned threshold_fill_exp2 = 2;
  
    /* The threshold of minimum page fill factor, as a number of free bytes on a
     * page. Pages emptier than this are candidates for merging. */
    const unsigned room_threshold =
        page_space(mc->mc_txn->mt_env) -
        (page_space(mc->mc_txn->mt_env) >> threshold_fill_exp2);
  
    const MDBX_page *const tp = mc->mc_pg[mc->mc_top];
    mdbx_debug("rebalancing %s page %" PRIaPGNO " (has %u keys, %.1f%% full)",
               (pagetype & P_LEAF) ? "leaf" : "branch", tp->mp_pgno,
               page_numkeys(tp), page_fill(mc->mc_txn->mt_env, tp));
  
    if (unlikely(page_numkeys(tp) < minkeys)) {
      mdbx_debug("page %" PRIaPGNO " must be merged due keys < %u threshold",
                 tp->mp_pgno, minkeys);
    } else if (unlikely(page_room(tp) > room_threshold)) {
      mdbx_debug("page %" PRIaPGNO " should be merged due room %u > %u threshold",
                 tp->mp_pgno, page_room(tp), room_threshold);
    } else {
      mdbx_debug("no need to rebalance page %" PRIaPGNO
                 ", room %u < %u threshold",
                 tp->mp_pgno, page_room(tp), room_threshold);
      mdbx_cassert(mc, mc->mc_db->md_entries > 0);
      return MDBX_SUCCESS;
    }
  
    int rc;
    if (mc->mc_snum < 2) {
      MDBX_page *const mp = mc->mc_pg[0];
      const unsigned nkeys = page_numkeys(mp);
      mdbx_cassert(mc, (mc->mc_db->md_entries == 0) == (nkeys == 0));
      if (IS_SUBP(mp)) {
        mdbx_debug("%s", "Can't rebalance a subpage, ignoring");
        mdbx_cassert(mc, pagetype & P_LEAF);
        return MDBX_SUCCESS;
      }
      if (nkeys == 0) {
        mdbx_cassert(mc, IS_LEAF(mp));
        mdbx_debug("%s", "tree is completely empty");
        mc->mc_db->md_root = P_INVALID;
        mc->mc_db->md_depth = 0;
        mdbx_cassert(mc, mc->mc_db->md_branch_pages == 0 &&
                             mc->mc_db->md_overflow_pages == 0 &&
                             mc->mc_db->md_leaf_pages == 1);
        /* Adjust cursors pointing to mp */
        for (MDBX_cursor *m2 = mc->mc_txn->tw.cursors[mc->mc_dbi]; m2;
             m2 = m2->mc_next) {
          MDBX_cursor *m3 =
              (mc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
          if (m3 == mc || !(m3->mc_flags & C_INITIALIZED))
            continue;
          if (m3->mc_pg[0] == mp) {
            m3->mc_snum = 0;
            m3->mc_top = 0;
            m3->mc_flags &= ~C_INITIALIZED;
          }
        }
        mc->mc_snum = 0;
        mc->mc_top = 0;
        mc->mc_flags &= ~C_INITIALIZED;
  
        rc = mdbx_page_retire(mc, mp);
        if (unlikely(rc != MDBX_SUCCESS))
          return rc;
      } else if (IS_BRANCH(mp) && nkeys == 1) {
        mdbx_debug("%s", "collapsing root page!");
        mc->mc_db->md_root = node_pgno(page_node(mp, 0));
        rc = mdbx_page_get(mc, mc->mc_db->md_root, &mc->mc_pg[0], NULL,
                           pp_txnid4chk(mp, mc->mc_txn));
        if (unlikely(rc != MDBX_SUCCESS))
          return rc;
        mc->mc_db->md_depth--;
        mc->mc_ki[0] = mc->mc_ki[1];
        for (int i = 1; i < mc->mc_db->md_depth; i++) {
          mc->mc_pg[i] = mc->mc_pg[i + 1];
          mc->mc_ki[i] = mc->mc_ki[i + 1];
        }
  
        /* Adjust other cursors pointing to mp */
        for (MDBX_cursor *m2 = mc->mc_txn->tw.cursors[mc->mc_dbi]; m2;
             m2 = m2->mc_next) {
          MDBX_cursor *m3 =
              (mc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
          if (m3 == mc || !(m3->mc_flags & C_INITIALIZED))
            continue;
          if (m3->mc_pg[0] == mp) {
            for (int i = 0; i < mc->mc_db->md_depth; i++) {
              m3->mc_pg[i] = m3->mc_pg[i + 1];
              m3->mc_ki[i] = m3->mc_ki[i + 1];
            }
            m3->mc_snum--;
            m3->mc_top--;
          }
        }
        mdbx_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]) ||
                             PAGETYPE(mc->mc_pg[mc->mc_top]) == pagetype);
        mdbx_cassert(mc, mc->mc_snum < mc->mc_db->md_depth ||
                             IS_LEAF(mc->mc_pg[mc->mc_db->md_depth - 1]));
  
        rc = mdbx_page_retire(mc, mp);
        if (unlikely(rc != MDBX_SUCCESS))
          return rc;
      } else {
        mdbx_debug("root page %" PRIaPGNO
                   " doesn't need rebalancing (flags 0x%x)",
                   mp->mp_pgno, mp->mp_flags);
      }
      return MDBX_SUCCESS;
    }
  
    /* The parent (branch page) must have at least 2 pointers,
     * otherwise the tree is invalid. */
    const unsigned pre_top = mc->mc_top - 1;
    mdbx_cassert(mc, IS_BRANCH(mc->mc_pg[pre_top]));
    mdbx_cassert(mc, !IS_SUBP(mc->mc_pg[0]));
    mdbx_cassert(mc, page_numkeys(mc->mc_pg[pre_top]) > 1);
  
    /* Leaf page fill factor is below the threshold.
     * Try to move keys from left or right neighbor, or
     * merge with a neighbor page. */
  
    /* Find neighbors. */
    MDBX_cursor mn;
    cursor_copy_internal(mc, &mn);
    mn.mc_xcursor = NULL;
  
    MDBX_page *left = nullptr, *right = nullptr;
    if (mn.mc_ki[pre_top] > 0) {
      rc = mdbx_page_get(
          &mn, node_pgno(page_node(mn.mc_pg[pre_top], mn.mc_ki[pre_top] - 1)),
          &left, NULL, pp_txnid4chk(mn.mc_pg[pre_top], mc->mc_txn));
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      mdbx_cassert(mc, PAGETYPE(left) == PAGETYPE(mc->mc_pg[mc->mc_top]));
    }
    if (mn.mc_ki[pre_top] + 1u < page_numkeys(mn.mc_pg[pre_top])) {
      rc = mdbx_page_get(
          &mn, node_pgno(page_node(mn.mc_pg[pre_top], mn.mc_ki[pre_top] + 1)),
          &right, NULL, pp_txnid4chk(mn.mc_pg[pre_top], mc->mc_txn));
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      mdbx_cassert(mc, PAGETYPE(right) == PAGETYPE(mc->mc_pg[mc->mc_top]));
    }
  
    const indx_t ki_top = mc->mc_ki[mc->mc_top];
    const indx_t ki_pre_top = mn.mc_ki[pre_top];
    const indx_t nkeys = (indx_t)page_numkeys(mn.mc_pg[mn.mc_top]);
    if (left && page_room(left) > room_threshold &&
        (!right || page_room(right) < page_room(left))) {
      /* try merge with left */
      mdbx_cassert(mc, page_numkeys(left) >= minkeys);
      mn.mc_pg[mn.mc_top] = left;
      mn.mc_ki[mn.mc_top - 1] = ki_pre_top - 1;
      mn.mc_ki[mn.mc_top] = (indx_t)(page_numkeys(left) - 1);
      mc->mc_ki[mc->mc_top] = 0;
      const indx_t new_ki = (indx_t)(ki_top + page_numkeys(left));
      mn.mc_ki[mn.mc_top] += mc->mc_ki[mn.mc_top] + 1;
      /* We want mdbx_rebalance to find mn when doing fixups */
      WITH_CURSOR_TRACKING(mn, rc = mdbx_page_merge(mc, &mn));
      if (likely(rc != MDBX_RESULT_TRUE)) {
        cursor_copy_internal(&mn, mc);
        mc->mc_ki[mc->mc_top] = new_ki;
        mdbx_cassert(mc, rc || page_numkeys(mc->mc_pg[mc->mc_top]) >= minkeys);
        return rc;
      }
    }
    if (right && page_room(right) > room_threshold) {
      /* try merge with right */
      mdbx_cassert(mc, page_numkeys(right) >= minkeys);
      mn.mc_pg[mn.mc_top] = right;
      mn.mc_ki[mn.mc_top - 1] = ki_pre_top + 1;
      mn.mc_ki[mn.mc_top] = 0;
      mc->mc_ki[mc->mc_top] = nkeys;
      WITH_CURSOR_TRACKING(mn, rc = mdbx_page_merge(&mn, mc));
      if (likely(rc != MDBX_RESULT_TRUE)) {
        mc->mc_ki[mc->mc_top] = ki_top;
        mdbx_cassert(mc, rc || page_numkeys(mc->mc_pg[mc->mc_top]) >= minkeys);
        return rc;
      }
    }
    if (left && page_numkeys(left) > minkeys &&
        (!right || page_numkeys(right) <= minkeys ||
         page_room(right) > page_room(left))) {
      /* try move from left */
      mn.mc_pg[mn.mc_top] = left;
      mn.mc_ki[mn.mc_top - 1] = ki_pre_top - 1;
      mn.mc_ki[mn.mc_top] = (indx_t)(page_numkeys(left) - 1);
      mc->mc_ki[mc->mc_top] = 0;
      WITH_CURSOR_TRACKING(mn, rc = mdbx_node_move(&mn, mc, true));
      if (likely(rc != MDBX_RESULT_TRUE)) {
        mc->mc_ki[mc->mc_top] = ki_top + 1;
        mdbx_cassert(mc, rc || page_numkeys(mc->mc_pg[mc->mc_top]) >= minkeys);
        return rc;
      }
    }
    if (right && page_numkeys(right) > minkeys) {
      /* try move from right */
      mn.mc_pg[mn.mc_top] = right;
      mn.mc_ki[mn.mc_top - 1] = ki_pre_top + 1;
      mn.mc_ki[mn.mc_top] = 0;
      mc->mc_ki[mc->mc_top] = nkeys;
      WITH_CURSOR_TRACKING(mn, rc = mdbx_node_move(&mn, mc, false));
      if (likely(rc != MDBX_RESULT_TRUE)) {
        mc->mc_ki[mc->mc_top] = ki_top;
        mdbx_cassert(mc, rc || page_numkeys(mc->mc_pg[mc->mc_top]) >= minkeys);
        return rc;
      }
    }
  
    if (nkeys >= minkeys) {
  #if MDBX_DEBUG > 0
      if (mdbx_audit_enabled())
        return mdbx_cursor_check(mc, C_UPDATING);
  #endif
      return MDBX_SUCCESS;
    }
  
    if (left && (!right || page_room(left) > page_room(right))) {
      /* try merge with left */
      mdbx_cassert(mc, page_numkeys(left) >= minkeys);
      mn.mc_pg[mn.mc_top] = left;
      mn.mc_ki[mn.mc_top - 1] = ki_pre_top - 1;
      mn.mc_ki[mn.mc_top] = (indx_t)(page_numkeys(left) - 1);
      mc->mc_ki[mc->mc_top] = 0;
      const indx_t new_ki = (indx_t)(ki_top + page_numkeys(left));
      mn.mc_ki[mn.mc_top] += mc->mc_ki[mn.mc_top] + 1;
      /* We want mdbx_rebalance to find mn when doing fixups */
      WITH_CURSOR_TRACKING(mn, rc = mdbx_page_merge(mc, &mn));
      if (likely(rc != MDBX_RESULT_TRUE)) {
        cursor_copy_internal(&mn, mc);
        mc->mc_ki[mc->mc_top] = new_ki;
        mdbx_cassert(mc, rc || page_numkeys(mc->mc_pg[mc->mc_top]) >= minkeys);
        return rc;
      }
    }
    if (likely(right)) {
      /* try merge with right */
      mdbx_cassert(mc, page_numkeys(right) >= minkeys);
      mn.mc_pg[mn.mc_top] = right;
      mn.mc_ki[mn.mc_top - 1] = ki_pre_top + 1;
      mn.mc_ki[mn.mc_top] = 0;
      mc->mc_ki[mc->mc_top] = nkeys;
      WITH_CURSOR_TRACKING(mn, rc = mdbx_page_merge(&mn, mc));
      if (likely(rc != MDBX_RESULT_TRUE)) {
        mc->mc_ki[mc->mc_top] = ki_top;
        mdbx_cassert(mc, rc || page_numkeys(mc->mc_pg[mc->mc_top]) >= minkeys);
        return rc;
      }
    }
    return MDBX_PROBLEM;
  }
  
  static __cold int mdbx_page_check(MDBX_cursor *const mc,
                                    const MDBX_page *const mp, unsigned options) {
    options |= mc->mc_flags & (C_COPYING | C_UPDATING | C_RETIRING | C_SKIPORD);
    MDBX_env *const env = mc->mc_txn->mt_env;
    const unsigned nkeys = page_numkeys(mp);
    char *const end_of_page = (char *)mp + env->me_psize;
    if (unlikely(mp->mp_pgno < MIN_PAGENO || mp->mp_pgno > MAX_PAGENO))
      return bad_page(mp, "invalid pgno (%u)\n", mp->mp_pgno);
    if (IS_OVERFLOW(mp)) {
      if (unlikely(mp->mp_pages < 1 && mp->mp_pages >= MAX_PAGENO / 2))
        return bad_page(mp, "invalid overflow n-pages (%u)\n", mp->mp_pages);
      if (unlikely(mp->mp_pgno > mc->mc_txn->mt_next_pgno - mp->mp_pages))
        return bad_page(mp, "overflow page beyond (%u) next-pgno\n",
                        mp->mp_pgno + mp->mp_pages);
      return MDBX_SUCCESS;
    }
  
    int rc = MDBX_SUCCESS;
    if ((options & C_UPDATING) == 0 || !IS_DIRTY(mp)) {
      if (unlikely(nkeys < 2 && IS_BRANCH(mp)))
        rc = bad_page(mp, "branch-page nkey (%u) < 2\n", nkeys);
    }
  
    MDBX_val here, prev = {0, 0};
    for (unsigned i = 0; i < nkeys; ++i) {
      if (IS_LEAF2(mp)) {
        const size_t ksize = mp->mp_leaf2_ksize;
        char *const key = page_leaf2key(mp, i, ksize);
        if (unlikely(end_of_page < key + ksize)) {
          rc = bad_page(mp, "leaf2-key beyond (%zu) page-end\n",
                        key + ksize - end_of_page);
          continue;
        }
  
        if ((options & C_COPYING) == 0) {
          if (unlikely(ksize != mc->mc_dbx->md_klen_min)) {
            if (unlikely(ksize < mc->mc_dbx->md_klen_min ||
                         ksize > mc->mc_dbx->md_klen_max))
              rc = bad_page(
                  mp, "leaf2-key size (%zu) <> min/max key-length (%zu/%zu)\n",
                  ksize, mc->mc_dbx->md_klen_min, mc->mc_dbx->md_klen_max);
            else
              mc->mc_dbx->md_klen_min = mc->mc_dbx->md_klen_max = ksize;
          }
          if ((options & C_SKIPORD) == 0) {
            here.iov_len = ksize;
            here.iov_base = key;
            if (prev.iov_base && unlikely(mc->mc_dbx->md_cmp(&here, &prev) <= 0))
              rc = bad_page(mp, "leaf2-key #%u wrong order\n", i);
            prev = here;
          }
        }
      } else {
        const MDBX_node *const node = page_node(mp, i);
        const char *node_end = (char *)node + NODESIZE;
        if (unlikely(node_end > end_of_page)) {
          rc = bad_page(mp, "node (%zu) beyond page-end\n",
                        node_end - end_of_page);
          continue;
        }
        if (IS_LEAF(mp) || i > 0) {
          size_t ksize = node_ks(node);
          char *key = node_key(node);
          if (unlikely(end_of_page < key + ksize)) {
            rc = bad_page(mp, "node-key (%zu) beyond page-end\n",
                          key + ksize - end_of_page);
            continue;
          }
  
          if ((options & C_COPYING) == 0) {
            if (unlikely(ksize < mc->mc_dbx->md_klen_min ||
                         ksize > mc->mc_dbx->md_klen_max))
              rc = bad_page(
                  mp, "node-key size (%zu) <> min/max key-length (%zu/%zu)\n",
                  ksize, mc->mc_dbx->md_klen_min, mc->mc_dbx->md_klen_max);
  
            if ((options & C_SKIPORD) == 0) {
              here.iov_base = key;
              here.iov_len = ksize;
              if (prev.iov_base &&
                  unlikely(mc->mc_dbx->md_cmp(&here, &prev) <= 0))
                rc = bad_page(mp, "node-key #%u wrong order\n", i);
              prev = here;
            }
          }
        }
        if (IS_BRANCH(mp)) {
          if ((options & C_RETIRING) == 0) {
            const pgno_t ref = node_pgno(node);
            if (unlikely(ref < MIN_PAGENO || ref >= mc->mc_txn->mt_next_pgno))
              rc = bad_page(mp, "branch-node wrong pgno (%u)\n", ref);
          }
          continue;
        }
  
        switch (node_flags(node)) {
        default:
          rc = bad_page(mp, "invalid node flags (%u)\n", node_flags(node));
          break;
        case F_BIGDATA /* data on large-page */:
        case 0 /* usual */:
        case F_SUBDATA /* sub-db */:
        case F_SUBDATA | F_DUPDATA /* dupsorted sub-tree */:
        case F_DUPDATA /* short sub-page */:
          break;
        }
  
        if (node_flags(node) & F_BIGDATA) {
          const size_t dsize = node_ds(node);
          if ((options & C_COPYING) == 0) {
            if (unlikely(dsize <= mc->mc_dbx->md_vlen_min ||
                         dsize > mc->mc_dbx->md_vlen_max))
              rc = bad_page(
                  mp,
                  "big-node data size (%zu) <> min/max value-length (%zu/%zu)\n",
                  dsize, mc->mc_dbx->md_vlen_min, mc->mc_dbx->md_vlen_max);
          }
          if ((options & C_RETIRING) == 0) {
            MDBX_page *lp;
            int err = mdbx_page_get(mc, node_largedata_pgno(node), &lp, NULL,
                                    pp_txnid4chk(mp, mc->mc_txn));
            if (unlikely(err != MDBX_SUCCESS))
              return err;
            if (unlikely(!IS_OVERFLOW(lp))) {
              rc = bad_page(mp, "big-node refs to non-overflow page (%u)\n",
                            lp->mp_pgno);
              continue;
            }
            if (unlikely(number_of_ovpages(env, dsize) > lp->mp_pages))
              rc =
                  bad_page(mp, "big-node size (%zu) mismatch n-pages size (%u)\n",
                           dsize, lp->mp_pages);
          }
          continue;
        }
  
        const size_t dsize = node_ds(node);
        const char *const data = node_data(node);
        if (unlikely(end_of_page < data + dsize)) {
          rc = bad_page(mp,
                        "node-data(%u of %u, %zu bytes) beyond (%zu) page-end\n",
                        i, nkeys, dsize, data + dsize - end_of_page);
          continue;
        }
  
        switch (node_flags(node)) {
        default:
          /* wrong, but already handled */
          continue;
        case 0 /* usual */:
          if ((options & C_COPYING) == 0) {
            if (unlikely(dsize < mc->mc_dbx->md_vlen_min ||
                         dsize > mc->mc_dbx->md_vlen_max)) {
              rc = bad_page(
                  mp, "node-data size (%zu) <> min/max value-length (%zu/%zu)\n",
                  dsize, mc->mc_dbx->md_vlen_min, mc->mc_dbx->md_vlen_max);
              continue;
            }
          }
          break;
        case F_SUBDATA /* sub-db */:
          if (unlikely(dsize != sizeof(MDBX_db))) {
            rc = bad_page(mp, "invalid sub-db record size (%zu)\n", dsize);
            continue;
          }
          break;
        case F_SUBDATA | F_DUPDATA /* dupsorted sub-tree */:
          if (unlikely(dsize != sizeof(MDBX_db))) {
            rc = bad_page(mp, "invalid nested-db record size (%zu)\n", dsize);
            continue;
          }
          break;
        case F_DUPDATA /* short sub-page */:
          if (unlikely(dsize <= PAGEHDRSZ)) {
            rc = bad_page(mp, "invalid nested-page record size (%zu)\n", dsize);
            continue;
          } else {
            const MDBX_page *const sp = (MDBX_page *)data;
            const char *const end_of_subpage = data + dsize;
            const int nsubkeys = page_numkeys(sp);
            switch (sp->mp_flags & ~P_DIRTY /* ignore for sub-pages */) {
            case P_LEAF | P_SUBP:
            case P_LEAF | P_LEAF2 | P_SUBP:
              break;
            default:
              rc = bad_page(mp, "invalid nested-page flags (%u)\n", sp->mp_flags);
              continue;
            }
  
            MDBX_val sub_here, sub_prev = {0, 0};
            for (int j = 0; j < nsubkeys; j++) {
              if (IS_LEAF2(sp)) {
                /* LEAF2 pages have no mp_ptrs[] or node headers */
                size_t sub_ksize = sp->mp_leaf2_ksize;
                char *sub_key = page_leaf2key(sp, j, sub_ksize);
                if (unlikely(end_of_subpage < sub_key + sub_ksize)) {
                  rc = bad_page(mp, "nested-leaf2-key beyond (%zu) nested-page\n",
                                sub_key + sub_ksize - end_of_subpage);
                  continue;
                }
  
                if ((options & C_COPYING) == 0) {
                  if (unlikely(sub_ksize != mc->mc_dbx->md_vlen_min)) {
                    if (unlikely(sub_ksize < mc->mc_dbx->md_vlen_min ||
                                 sub_ksize > mc->mc_dbx->md_vlen_max)) {
                      rc = bad_page(mp,
                                    "nested-leaf2-key size (%zu) <> min/max "
                                    "value-length (%zu/%zu)\n",
                                    sub_ksize, mc->mc_dbx->md_vlen_min,
                                    mc->mc_dbx->md_vlen_max);
                      continue;
                    }
                    mc->mc_dbx->md_vlen_min = mc->mc_dbx->md_vlen_max = sub_ksize;
                  }
                  if ((options & C_SKIPORD) == 0) {
                    sub_here.iov_len = sub_ksize;
                    sub_here.iov_base = sub_key;
                    if (sub_prev.iov_base &&
                        unlikely(mc->mc_dbx->md_dcmp(&sub_prev, &sub_here) >= 0))
                      rc = bad_page(mp, "nested-leaf2-key #%u wrong order\n", j);
                    sub_prev = sub_here;
                  }
                }
              } else {
                const MDBX_node *const sub_node = page_node(sp, j);
                const char *sub_node_end = (char *)sub_node + NODESIZE;
                if (unlikely(sub_node_end > end_of_subpage)) {
                  rc = bad_page(mp, "nested-node beyond (%zu) nested-page\n",
                                end_of_subpage - sub_node_end);
                  continue;
                }
                if (unlikely(node_flags(sub_node) != 0))
                  rc = bad_page(mp, "nested-node invalid flags (%u)\n",
                                node_flags(sub_node));
  
                size_t sub_ksize = node_ks(sub_node);
                char *sub_key = node_key(sub_node);
                size_t sub_dsize = node_ds(sub_node);
                /* char *sub_data = node_data(sub_node); */
  
                if ((options & C_COPYING) == 0) {
                  if (unlikely(sub_ksize < mc->mc_dbx->md_vlen_min ||
                               sub_ksize > mc->mc_dbx->md_vlen_max))
                    rc = bad_page(mp,
                                  "nested-node-key size (%zu) <> min/max "
                                  "value-length (%zu/%zu)\n",
                                  sub_ksize, mc->mc_dbx->md_vlen_min,
                                  mc->mc_dbx->md_vlen_max);
  
                  if ((options & C_SKIPORD) == 0) {
                    sub_here.iov_len = sub_ksize;
                    sub_here.iov_base = sub_key;
                    if (sub_prev.iov_base &&
                        unlikely(mc->mc_dbx->md_dcmp(&sub_prev, &sub_here) >= 0))
                      rc = bad_page(mp, "nested-node-key #%u wrong order\n", j);
                    sub_prev = sub_here;
                  }
                }
                if (unlikely(sub_dsize != 0))
                  rc = bad_page(mp, "nested-node non-empty data size (%zu)\n",
                                sub_dsize);
                if (unlikely(end_of_subpage < sub_key + sub_ksize))
                  rc = bad_page(mp, "nested-node-key beyond (%zu) nested-page\n",
                                sub_key + sub_ksize - end_of_subpage);
              }
            }
          }
          break;
        }
      }
    }
    return rc;
  }
  
  static __cold int mdbx_cursor_check(MDBX_cursor *mc, unsigned options) {
    mdbx_tassert(mc->mc_txn, mc->mc_txn->mt_parent ||
                                 mc->mc_txn->tw.dirtyroom +
                                         mc->mc_txn->tw.dirtylist->length ==
                                     MDBX_DPL_TXNFULL);
    mdbx_cassert(mc, mc->mc_top == mc->mc_snum - 1);
    if (unlikely(mc->mc_top != mc->mc_snum - 1))
      return MDBX_CURSOR_FULL;
    mdbx_cassert(mc, (options & C_UPDATING) ? mc->mc_snum <= mc->mc_db->md_depth
                                            : mc->mc_snum == mc->mc_db->md_depth);
    if (unlikely((options & C_UPDATING) ? mc->mc_snum > mc->mc_db->md_depth
                                        : mc->mc_snum != mc->mc_db->md_depth))
      return MDBX_CURSOR_FULL;
  
    for (int n = 0; n < (int)mc->mc_snum; ++n) {
      MDBX_page *mp = mc->mc_pg[n];
      const unsigned nkeys = page_numkeys(mp);
      const bool expect_branch = (n < mc->mc_db->md_depth - 1) ? true : false;
      const bool expect_nested_leaf =
          (n + 1 == mc->mc_db->md_depth - 1) ? true : false;
      const bool branch = IS_BRANCH(mp) ? true : false;
      mdbx_cassert(mc, branch == expect_branch);
      if (unlikely(branch != expect_branch))
        return MDBX_CURSOR_FULL;
      if ((options & C_UPDATING) == 0) {
        mdbx_cassert(mc,
                     nkeys > mc->mc_ki[n] || (!branch && nkeys == mc->mc_ki[n] &&
                                              (mc->mc_flags & C_EOF) != 0));
        if (unlikely(nkeys <= mc->mc_ki[n] &&
                     !(!branch && nkeys == mc->mc_ki[n] &&
                       (mc->mc_flags & C_EOF) != 0)))
          return MDBX_CURSOR_FULL;
      } else {
        mdbx_cassert(mc, nkeys + 1 >= mc->mc_ki[n]);
        if (unlikely(nkeys + 1 < mc->mc_ki[n]))
          return MDBX_CURSOR_FULL;
      }
  
      int err = mdbx_page_check(mc, mp, options);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
  
      for (unsigned i = 0; i < nkeys; ++i) {
        if (branch) {
          MDBX_node *node = page_node(mp, i);
          mdbx_cassert(mc, node_flags(node) == 0);
          if (unlikely(node_flags(node) != 0))
            return MDBX_CURSOR_FULL;
          pgno_t pgno = node_pgno(node);
          MDBX_page *np;
          int rc =
              mdbx_page_get(mc, pgno, &np, NULL, pp_txnid4chk(mp, mc->mc_txn));
          mdbx_cassert(mc, rc == MDBX_SUCCESS);
          if (unlikely(rc != MDBX_SUCCESS))
            return rc;
          const bool nested_leaf = IS_LEAF(np) ? true : false;
          mdbx_cassert(mc, nested_leaf == expect_nested_leaf);
          if (unlikely(nested_leaf != expect_nested_leaf))
            return MDBX_CURSOR_FULL;
          err = mdbx_page_check(mc, np, options);
          if (unlikely(err != MDBX_SUCCESS))
            return err;
        }
      }
    }
    return MDBX_SUCCESS;
  }
  
  /* Complete a delete operation started by mdbx_cursor_del(). */
  static int mdbx_cursor_del0(MDBX_cursor *mc) {
    int rc;
    MDBX_page *mp;
    indx_t ki;
    unsigned nkeys;
    MDBX_dbi dbi = mc->mc_dbi;
  
    mdbx_cassert(mc, cursor_is_tracked(mc));
    mdbx_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]));
    ki = mc->mc_ki[mc->mc_top];
    mp = mc->mc_pg[mc->mc_top];
    mdbx_node_del(mc, mc->mc_db->md_xsize);
    mc->mc_db->md_entries--;
  
    /* Adjust other cursors pointing to mp */
    for (MDBX_cursor *m2 = mc->mc_txn->tw.cursors[dbi]; m2; m2 = m2->mc_next) {
      MDBX_cursor *m3 = (mc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
      if (m3 == mc || !(m2->mc_flags & m3->mc_flags & C_INITIALIZED))
        continue;
      if (m3->mc_snum < mc->mc_snum)
        continue;
      if (m3->mc_pg[mc->mc_top] == mp) {
        if (m3->mc_ki[mc->mc_top] == ki) {
          m3->mc_flags |= C_DEL;
          if (mc->mc_db->md_flags & MDBX_DUPSORT) {
            /* Sub-cursor referred into dataset which is gone */
            m3->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);
          }
          continue;
        } else if (m3->mc_ki[mc->mc_top] > ki) {
          m3->mc_ki[mc->mc_top]--;
        }
        if (XCURSOR_INITED(m3))
          XCURSOR_REFRESH(m3, m3->mc_pg[mc->mc_top], m3->mc_ki[mc->mc_top]);
      }
    }
  
    rc = mdbx_rebalance(mc);
    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout;
  
    if (unlikely(!mc->mc_snum)) {
      /* DB is totally empty now, just bail out.
       * Other cursors adjustments were already done
       * by mdbx_rebalance and aren't needed here. */
      mdbx_cassert(mc, mc->mc_db->md_entries == 0 && mc->mc_db->md_depth == 0 &&
                           mc->mc_db->md_root == P_INVALID);
      mc->mc_flags |= C_EOF;
      return MDBX_SUCCESS;
    }
  
    ki = mc->mc_ki[mc->mc_top];
    mp = mc->mc_pg[mc->mc_top];
    mdbx_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]));
    nkeys = page_numkeys(mp);
    mdbx_cassert(mc, (mc->mc_db->md_entries > 0 && nkeys > 0) ||
                         ((mc->mc_flags & C_SUB) && mc->mc_db->md_entries == 0 &&
                          nkeys == 0));
  
    /* Adjust this and other cursors pointing to mp */
    for (MDBX_cursor *m2 = mc->mc_txn->tw.cursors[dbi]; m2; m2 = m2->mc_next) {
      MDBX_cursor *m3 = (mc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
      if (!(m2->mc_flags & m3->mc_flags & C_INITIALIZED))
        continue;
      if (m3->mc_snum < mc->mc_snum)
        continue;
      if (m3->mc_pg[mc->mc_top] == mp) {
        /* if m3 points past last node in page, find next sibling */
        if (m3->mc_ki[mc->mc_top] >= nkeys) {
          rc = mdbx_cursor_sibling(m3, SIBLING_RIGHT);
          if (rc == MDBX_NOTFOUND) {
            m3->mc_flags |= C_EOF;
            rc = MDBX_SUCCESS;
            continue;
          }
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
        }
        if (m3->mc_ki[mc->mc_top] >= ki ||
            /* moved to right sibling */ m3->mc_pg[mc->mc_top] != mp) {
          if (m3->mc_xcursor && !(m3->mc_flags & C_EOF)) {
            MDBX_node *node =
                page_node(m3->mc_pg[m3->mc_top], m3->mc_ki[m3->mc_top]);
            /* If this node has dupdata, it may need to be reinited
             * because its data has moved.
             * If the xcursor was not inited it must be reinited.
             * Else if node points to a subDB, nothing is needed. */
            if (node_flags(node) & F_DUPDATA) {
              if (m3->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) {
                if (!(node_flags(node) & F_SUBDATA))
                  m3->mc_xcursor->mx_cursor.mc_pg[0] = node_data(node);
              } else {
                rc = mdbx_xcursor_init1(m3, node, m3->mc_pg[m3->mc_top]);
                if (unlikely(rc != MDBX_SUCCESS))
                  goto bailout;
                rc = mdbx_cursor_first(&m3->mc_xcursor->mx_cursor, NULL, NULL);
                if (unlikely(rc != MDBX_SUCCESS))
                  goto bailout;
              }
            }
            m3->mc_xcursor->mx_cursor.mc_flags |= C_DEL;
          }
          m3->mc_flags |= C_DEL;
        }
      }
    }
  
    mdbx_cassert(mc, rc == MDBX_SUCCESS);
    if (mdbx_audit_enabled())
      rc = mdbx_cursor_check(mc, 0);
    return rc;
  
  bailout:
    mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
    return rc;
  }
  
  int mdbx_del(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
               const MDBX_val *data) {
    int rc = check_txn_rw(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!key))
      return MDBX_EINVAL;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    if (unlikely(txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_BLOCKED)))
      return (txn->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EACCESS : MDBX_BAD_TXN;
  
    return mdbx_del0(txn, dbi, key, data, 0);
  }
  
  static int mdbx_del0(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
                       const MDBX_val *data, unsigned flags) {
    MDBX_cursor_couple cx;
    MDBX_cursor_op op;
    MDBX_val rdata;
    int rc, exact = 0;
    DKBUF;
  
    mdbx_debug("====> delete db %u key [%s], data [%s]", dbi, DKEY(key),
               DVAL(data));
  
    rc = mdbx_cursor_init(&cx.outer, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (data) {
      op = MDBX_GET_BOTH;
      rdata = *data;
      data = &rdata;
    } else {
      op = MDBX_SET;
      flags |= MDBX_ALLDUPS;
    }
    rc =
        mdbx_cursor_set(&cx.outer, (MDBX_val *)key, (MDBX_val *)data, op, &exact);
    if (likely(rc == MDBX_SUCCESS)) {
      /* let mdbx_page_split know about this cursor if needed:
       * delete will trigger a rebalance; if it needs to move
       * a node from one page to another, it will have to
       * update the parent's separator key(s). If the new sepkey
       * is larger than the current one, the parent page may
       * run out of space, triggering a split. We need this
       * cursor to be consistent until the end of the rebalance. */
      cx.outer.mc_next = txn->tw.cursors[dbi];
      txn->tw.cursors[dbi] = &cx.outer;
      rc = mdbx_cursor_del(&cx.outer, flags);
      txn->tw.cursors[dbi] = cx.outer.mc_next;
    }
    return rc;
  }
  
  /* Split a page and insert a new node.
   * Set MDBX_TXN_ERROR on failure.
   * [in,out] mc Cursor pointing to the page and desired insertion index.
   * The cursor will be updated to point to the actual page and index where
   * the node got inserted after the split.
   * [in] newkey The key for the newly inserted node.
   * [in] newdata The data for the newly inserted node.
   * [in] newpgno The page number, if the new node is a branch node.
   * [in] nflags The NODE_ADD_FLAGS for the new node.
   * Returns 0 on success, non-zero on failure. */
  static int mdbx_page_split(MDBX_cursor *mc, const MDBX_val *newkey,
                             MDBX_val *newdata, pgno_t newpgno, unsigned nflags) {
    unsigned flags;
    int rc = MDBX_SUCCESS, foliage = 0, did_split = 0;
    pgno_t pgno = 0;
    unsigned i, ptop;
    MDBX_env *env = mc->mc_txn->mt_env;
    MDBX_val sepkey, rkey, xdata;
    MDBX_page *copy = NULL;
    MDBX_page *rp, *pp;
    MDBX_cursor mn;
    DKBUF;
  
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    unsigned newindx = mc->mc_ki[mc->mc_top];
    unsigned nkeys = page_numkeys(mp);
    if (mdbx_audit_enabled()) {
      rc = mdbx_cursor_check(mc, C_UPDATING);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  
    mdbx_cassert(mc,
                 nkeys >= (unsigned)(IS_BRANCH(mp) ? MDBX_MINKEYS * 2 - 1 : 1));
    mdbx_debug("-----> splitting %s page %" PRIaPGNO
               " and adding [%s] at index %i/%i",
               IS_LEAF(mp) ? "leaf" : "branch", mp->mp_pgno, DKEY(newkey),
               mc->mc_ki[mc->mc_top], nkeys);
  
    /* Create a right sibling. */
    if ((rc = mdbx_page_new(mc, mp->mp_flags, 1, &rp)))
      return rc;
    rp->mp_leaf2_ksize = mp->mp_leaf2_ksize;
    mdbx_debug("new right sibling: page %" PRIaPGNO, rp->mp_pgno);
  
    /* Usually when splitting the root page, the cursor
     * height is 1. But when called from mdbx_update_key,
     * the cursor height may be greater because it walks
     * up the stack while finding the branch slot to update. */
    if (mc->mc_top < 1) {
      if ((rc = mdbx_page_new(mc, P_BRANCH, 1, &pp)))
        goto done;
      /* shift current top to make room for new parent */
      mdbx_cassert(mc, mc->mc_snum < 2 && mc->mc_db->md_depth > 0);
      mc->mc_pg[2] = mc->mc_pg[1];
      mc->mc_ki[2] = mc->mc_ki[1];
      mc->mc_pg[1] = mc->mc_pg[0];
      mc->mc_ki[1] = mc->mc_ki[0];
      mc->mc_pg[0] = pp;
      mc->mc_ki[0] = 0;
      mc->mc_db->md_root = pp->mp_pgno;
      mdbx_debug("root split! new root = %" PRIaPGNO, pp->mp_pgno);
      foliage = mc->mc_db->md_depth++;
  
      /* Add left (implicit) pointer. */
      if (unlikely((rc = mdbx_node_add_branch(mc, 0, NULL, mp->mp_pgno)) !=
                   MDBX_SUCCESS)) {
        /* undo the pre-push */
        mc->mc_pg[0] = mc->mc_pg[1];
        mc->mc_ki[0] = mc->mc_ki[1];
        mc->mc_db->md_root = mp->mp_pgno;
        mc->mc_db->md_depth--;
        goto done;
      }
      mc->mc_snum++;
      mc->mc_top++;
      ptop = 0;
    } else {
      ptop = mc->mc_top - 1;
      mdbx_debug("parent branch page is %" PRIaPGNO, mc->mc_pg[ptop]->mp_pgno);
    }
  
    cursor_copy_internal(mc, &mn);
    mn.mc_xcursor = NULL;
    mn.mc_pg[mn.mc_top] = rp;
    mn.mc_ki[mn.mc_top] = 0;
    mn.mc_ki[ptop] = mc->mc_ki[ptop] + 1;
  
    unsigned split_indx;
    if (nflags & MDBX_APPEND) {
      mn.mc_ki[mn.mc_top] = 0;
      sepkey = *newkey;
      split_indx = newindx;
      nkeys = 0;
    } else {
      split_indx = (nkeys + 1) / 2;
      if (IS_LEAF2(rp)) {
        char *split, *ins;
        unsigned lsize, rsize, ksize;
        /* Move half of the keys to the right sibling */
        const int x = mc->mc_ki[mc->mc_top] - split_indx;
        ksize = mc->mc_db->md_xsize;
        split = page_leaf2key(mp, split_indx, ksize);
        rsize = (nkeys - split_indx) * ksize;
        lsize = (nkeys - split_indx) * sizeof(indx_t);
        mdbx_cassert(mc, mp->mp_lower >= lsize);
        mp->mp_lower -= (indx_t)lsize;
        mdbx_cassert(mc, rp->mp_lower + lsize <= UINT16_MAX);
        rp->mp_lower += (indx_t)lsize;
        mdbx_cassert(mc, mp->mp_upper + rsize - lsize <= UINT16_MAX);
        mp->mp_upper += (indx_t)(rsize - lsize);
        mdbx_cassert(mc, rp->mp_upper >= rsize - lsize);
        rp->mp_upper -= (indx_t)(rsize - lsize);
        sepkey.iov_len = ksize;
        if (newindx == split_indx) {
          sepkey.iov_base = newkey->iov_base;
        } else {
          sepkey.iov_base = split;
        }
        if (x < 0) {
          mdbx_cassert(mc, ksize >= sizeof(indx_t));
          ins = page_leaf2key(mp, mc->mc_ki[mc->mc_top], ksize);
          memcpy(rp->mp_ptrs, split, rsize);
          sepkey.iov_base = rp->mp_ptrs;
          memmove(ins + ksize, ins, (split_indx - mc->mc_ki[mc->mc_top]) * ksize);
          memcpy(ins, newkey->iov_base, ksize);
          mdbx_cassert(mc, UINT16_MAX - mp->mp_lower >= (int)sizeof(indx_t));
          mp->mp_lower += sizeof(indx_t);
          mdbx_cassert(mc, mp->mp_upper >= ksize - sizeof(indx_t));
          mp->mp_upper -= (indx_t)(ksize - sizeof(indx_t));
        } else {
          memcpy(rp->mp_ptrs, split, x * ksize);
          ins = page_leaf2key(rp, x, ksize);
          memcpy(ins, newkey->iov_base, ksize);
          memcpy(ins + ksize, split + x * ksize, rsize - x * ksize);
          mdbx_cassert(mc, UINT16_MAX - rp->mp_lower >= (int)sizeof(indx_t));
          rp->mp_lower += sizeof(indx_t);
          mdbx_cassert(mc, rp->mp_upper >= ksize - sizeof(indx_t));
          rp->mp_upper -= (indx_t)(ksize - sizeof(indx_t));
          mdbx_cassert(mc, x <= (int)UINT16_MAX);
          mc->mc_ki[mc->mc_top] = (indx_t)x;
        }
      } else {
        /* Maximum free space in an empty page */
        const unsigned pmax = page_space(env);
        const size_t nsize = IS_LEAF(mp) ? leaf_size(env, newkey, newdata)
                                         : branch_size(env, newkey);
  
        /* grab a page to hold a temporary copy */
        copy = mdbx_page_malloc(mc->mc_txn, 1);
        if (unlikely(copy == NULL)) {
          rc = MDBX_ENOMEM;
          goto done;
        }
        copy->mp_pgno = mp->mp_pgno;
        copy->mp_flags = mp->mp_flags;
        copy->mp_txnid = INVALID_TXNID;
        copy->mp_lower = 0;
        copy->mp_upper = (indx_t)page_space(env);
  
        /* prepare to insert */
        for (unsigned j = i = 0; i < nkeys; i++) {
          if (i == newindx)
            copy->mp_ptrs[j++] = 0;
          copy->mp_ptrs[j++] = mp->mp_ptrs[i];
        }
  
        /* When items are relatively large the split point needs
         * to be checked, because being off-by-one will make the
         * difference between success or failure in mdbx_node_add.
         *
         * It's also relevant if a page happens to be laid out
         * such that one half of its nodes are all "small" and
         * the other half of its nodes are "large." If the new
         * item is also "large" and falls on the half with
         * "large" nodes, it also may not fit.
         *
         * As a final tweak, if the new item goes on the last
         * spot on the page (and thus, onto the new page), bias
         * the split so the new page is emptier than the old page.
         * This yields better packing during sequential inserts. */
        if (nkeys < 32 || nsize > pmax / 16 || newindx >= nkeys) {
          /* Find split point */
          int dir;
          size_t psize = 0;
          unsigned k;
          if (newindx <= split_indx || newindx >= nkeys) {
            i = 0;
            dir = 1;
            k = (newindx >= nkeys) ? nkeys : split_indx + 1 + IS_LEAF(mp);
            split_indx = k - 1;
          } else {
            i = nkeys;
            dir = -1;
            k = split_indx - 1;
            split_indx += 1;
          }
          do {
            if (i == newindx) {
              psize += nsize;
            } else {
              MDBX_node *node =
                  (MDBX_node *)((char *)mp + copy->mp_ptrs[i] + PAGEHDRSZ);
              psize += NODESIZE + node_ks(node) + sizeof(indx_t);
              if (IS_LEAF(mp))
                psize += F_ISSET(node_flags(node), F_BIGDATA) ? sizeof(pgno_t)
                                                              : node_ds(node);
              psize = EVEN(psize);
            }
            if (psize > pmax) {
              split_indx = i + (dir < 0);
              break;
            }
            i += dir;
          } while (i != k);
        }
  
        if (split_indx == newindx) {
          sepkey.iov_len = newkey->iov_len;
          sepkey.iov_base = newkey->iov_base;
        } else {
          MDBX_node *node =
              (MDBX_node *)((char *)mp + copy->mp_ptrs[split_indx] + PAGEHDRSZ);
          sepkey.iov_len = node_ks(node);
          sepkey.iov_base = node_key(node);
        }
      }
    }
  
    mdbx_debug("separator is %d [%s]", split_indx, DKEY(&sepkey));
    if (mdbx_audit_enabled()) {
      rc = mdbx_cursor_check(mc, C_UPDATING);
      if (unlikely(rc != MDBX_SUCCESS))
        goto done;
      rc = mdbx_cursor_check(&mn, C_UPDATING);
      if (unlikely(rc != MDBX_SUCCESS))
        goto done;
    }
  
    /* Copy separator key to the parent. */
    if (page_room(mn.mc_pg[ptop]) < branch_size(env, &sepkey)) {
      const int snum = mc->mc_snum;
      const int depth = mc->mc_db->md_depth;
      mn.mc_snum--;
      mn.mc_top--;
      did_split = 1;
      /* We want other splits to find mn when doing fixups */
      WITH_CURSOR_TRACKING(
          mn, rc = mdbx_page_split(&mn, &sepkey, NULL, rp->mp_pgno, 0));
      if (unlikely(rc != MDBX_SUCCESS))
        goto done;
      mdbx_cassert(mc, (int)mc->mc_snum - snum == mc->mc_db->md_depth - depth);
      if (mdbx_audit_enabled()) {
        rc = mdbx_cursor_check(mc, C_UPDATING);
        if (unlikely(rc != MDBX_SUCCESS))
          goto done;
      }
  
      /* root split? */
      ptop += mc->mc_snum - snum;
  
      /* Right page might now have changed parent.
       * Check if left page also changed parent. */
      if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
          mc->mc_ki[ptop] >= page_numkeys(mc->mc_pg[ptop])) {
        for (i = 0; i < ptop; i++) {
          mc->mc_pg[i] = mn.mc_pg[i];
          mc->mc_ki[i] = mn.mc_ki[i];
        }
        mc->mc_pg[ptop] = mn.mc_pg[ptop];
        if (mn.mc_ki[ptop]) {
          mc->mc_ki[ptop] = mn.mc_ki[ptop] - 1;
        } else {
          /* find right page's left sibling */
          mc->mc_ki[ptop] = mn.mc_ki[ptop];
          rc = mdbx_cursor_sibling(mc, SIBLING_LEFT);
        }
      }
    } else {
      mn.mc_top--;
      rc = mdbx_node_add_branch(&mn, mn.mc_ki[ptop], &sepkey, rp->mp_pgno);
      mn.mc_top++;
    }
    if (unlikely(rc != MDBX_SUCCESS)) {
      if (rc == MDBX_NOTFOUND) /* improper mdbx_cursor_sibling() result */ {
        mdbx_error("unexpected %s", "MDBX_NOTFOUND");
        rc = MDBX_PROBLEM;
      }
      goto done;
    }
  
    if (nflags & MDBX_APPEND) {
      mc->mc_pg[mc->mc_top] = rp;
      mc->mc_ki[mc->mc_top] = 0;
      switch (PAGETYPE(rp)) {
      case P_BRANCH: {
        mdbx_cassert(mc, (nflags & (F_BIGDATA | F_SUBDATA | F_DUPDATA)) == 0);
        mdbx_cassert(mc, newpgno != 0 && newpgno != P_INVALID);
        rc = mdbx_node_add_branch(mc, 0, newkey, newpgno);
      } break;
      case P_LEAF: {
        mdbx_cassert(mc, newpgno == 0 || newpgno == P_INVALID);
        rc = mdbx_node_add_leaf(mc, 0, newkey, newdata, nflags);
      } break;
      case P_LEAF | P_LEAF2: {
        mdbx_cassert(mc, (nflags & (F_BIGDATA | F_SUBDATA | F_DUPDATA)) == 0);
        mdbx_cassert(mc, newpgno == 0 || newpgno == P_INVALID);
        rc = mdbx_node_add_leaf2(mc, 0, newkey);
      } break;
      default:
        rc = bad_page(rp, "wrong page-type %u\n", PAGETYPE(rp));
      }
      if (rc)
        goto done;
      for (i = 0; i < mc->mc_top; i++)
        mc->mc_ki[i] = mn.mc_ki[i];
    } else if (!IS_LEAF2(mp)) {
      /* Move nodes */
      mc->mc_pg[mc->mc_top] = rp;
      i = split_indx;
      indx_t n = 0;
      do {
        MDBX_val *rdata = NULL;
        if (i == newindx) {
          rkey.iov_base = newkey->iov_base;
          rkey.iov_len = newkey->iov_len;
          if (IS_LEAF(mp)) {
            rdata = newdata;
          } else
            pgno = newpgno;
          flags = nflags;
          /* Update index for the new key. */
          mc->mc_ki[mc->mc_top] = n;
        } else {
          MDBX_node *node =
              (MDBX_node *)((char *)mp + copy->mp_ptrs[i] + PAGEHDRSZ);
          rkey.iov_base = node_key(node);
          rkey.iov_len = node_ks(node);
          if (IS_LEAF(mp)) {
            xdata.iov_base = node_data(node);
            xdata.iov_len = node_ds(node);
            rdata = &xdata;
          } else
            pgno = node_pgno(node);
          flags = node_flags(node);
        }
  
        switch (PAGETYPE(rp)) {
        case P_BRANCH: {
          mdbx_cassert(mc, 0 == (uint16_t)flags);
          if (n == 0) {
            /* First branch index doesn't need key data. */
            rkey.iov_len = 0;
          }
          rc = mdbx_node_add_branch(mc, n, &rkey, pgno);
        } break;
        case P_LEAF: {
          mdbx_cassert(mc, pgno == 0);
          mdbx_cassert(mc, rdata != NULL);
          rc = mdbx_node_add_leaf(mc, n, &rkey, rdata, flags);
        } break;
        /* case P_LEAF | P_LEAF2: {
          mdbx_cassert(mc, (nflags & (F_BIGDATA | F_SUBDATA | F_DUPDATA)) == 0);
          mdbx_cassert(mc, gno == 0);
          rc = mdbx_node_add_leaf2(mc, n, &rkey);
        } break; */
        default:
          rc = bad_page(rp, "wrong page-type %u\n", PAGETYPE(rp));
        }
        if (rc)
          goto done;
  
        if (i == nkeys) {
          i = 0;
          n = 0;
          mc->mc_pg[mc->mc_top] = copy;
        } else {
          i++;
          n++;
        }
      } while (i != split_indx);
  
      nkeys = page_numkeys(copy);
      for (i = 0; i < nkeys; i++)
        mp->mp_ptrs[i] = copy->mp_ptrs[i];
      mp->mp_lower = copy->mp_lower;
      mp->mp_upper = copy->mp_upper;
      memcpy(page_node(mp, nkeys - 1), page_node(copy, nkeys - 1),
             env->me_psize - copy->mp_upper - PAGEHDRSZ);
  
      /* reset back to original page */
      if (newindx < split_indx) {
        mc->mc_pg[mc->mc_top] = mp;
      } else {
        mc->mc_pg[mc->mc_top] = rp;
        mc->mc_ki[ptop]++;
        /* Make sure mc_ki is still valid. */
        if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
            mc->mc_ki[ptop] >= page_numkeys(mc->mc_pg[ptop])) {
          for (i = 0; i <= ptop; i++) {
            mc->mc_pg[i] = mn.mc_pg[i];
            mc->mc_ki[i] = mn.mc_ki[i];
          }
        }
      }
      if (nflags & MDBX_RESERVE) {
        MDBX_node *node = page_node(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
        if (!(node_flags(node) & F_BIGDATA))
          newdata->iov_base = node_data(node);
      }
    } else {
      if (newindx >= split_indx) {
        mc->mc_pg[mc->mc_top] = rp;
        mc->mc_ki[ptop]++;
        /* Make sure mc_ki is still valid. */
        if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
            mc->mc_ki[ptop] >= page_numkeys(mc->mc_pg[ptop])) {
          for (i = 0; i <= ptop; i++) {
            mc->mc_pg[i] = mn.mc_pg[i];
            mc->mc_ki[i] = mn.mc_ki[i];
          }
        }
      }
    }
  
    {
      /* Adjust other cursors pointing to mp */
      MDBX_cursor *m2, *m3;
      MDBX_dbi dbi = mc->mc_dbi;
      nkeys = page_numkeys(mp);
  
      for (m2 = mc->mc_txn->tw.cursors[dbi]; m2; m2 = m2->mc_next) {
        m3 = (mc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
        if (m3 == mc)
          continue;
        if (!(m2->mc_flags & m3->mc_flags & C_INITIALIZED))
          continue;
        if (foliage) {
          int k;
          /* sub cursors may be on different DB */
          if (m3->mc_pg[0] != mp)
            continue;
          /* root split */
          for (k = foliage; k >= 0; k--) {
            m3->mc_ki[k + 1] = m3->mc_ki[k];
            m3->mc_pg[k + 1] = m3->mc_pg[k];
          }
          m3->mc_ki[0] = (m3->mc_ki[0] >= nkeys) ? 1 : 0;
          m3->mc_pg[0] = mc->mc_pg[0];
          m3->mc_snum++;
          m3->mc_top++;
        }
        if (m3->mc_top >= mc->mc_top && m3->mc_pg[mc->mc_top] == mp) {
          if (m3->mc_ki[mc->mc_top] >= newindx && !(nflags & MDBX_SPLIT_REPLACE))
            m3->mc_ki[mc->mc_top]++;
          if (m3->mc_ki[mc->mc_top] >= nkeys) {
            m3->mc_pg[mc->mc_top] = rp;
            mdbx_cassert(mc, m3->mc_ki[mc->mc_top] >= nkeys);
            m3->mc_ki[mc->mc_top] -= (indx_t)nkeys;
            for (i = 0; i < mc->mc_top; i++) {
              m3->mc_ki[i] = mn.mc_ki[i];
              m3->mc_pg[i] = mn.mc_pg[i];
            }
          }
        } else if (!did_split && m3->mc_top >= ptop &&
                   m3->mc_pg[ptop] == mc->mc_pg[ptop] &&
                   m3->mc_ki[ptop] >= mc->mc_ki[ptop]) {
          m3->mc_ki[ptop]++;
        }
        if (XCURSOR_INITED(m3) && IS_LEAF(mp))
          XCURSOR_REFRESH(m3, m3->mc_pg[mc->mc_top], m3->mc_ki[mc->mc_top]);
      }
    }
    mdbx_debug("mp left: %d, rp left: %d", page_room(mp), page_room(rp));
  
  done:
    if (copy) /* tmp page */
      mdbx_dpage_free(env, copy, 1);
    if (unlikely(rc))
      mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
    return rc;
  }
  
  int mdbx_put(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key, MDBX_val *data,
               unsigned flags) {
    int rc = check_txn_rw(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!key || !data))
      return MDBX_EINVAL;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    if (unlikely(flags & ~(MDBX_NOOVERWRITE | MDBX_NODUPDATA | MDBX_ALLDUPS |
                           MDBX_ALLDUPS | MDBX_RESERVE | MDBX_APPEND |
                           MDBX_APPENDDUP | MDBX_CURRENT | MDBX_MULTIPLE)))
      return MDBX_EINVAL;
  
    if (unlikely(txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_BLOCKED)))
      return (txn->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EACCESS : MDBX_BAD_TXN;
  
    MDBX_cursor_couple cx;
    rc = mdbx_cursor_init(&cx.outer, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
    cx.outer.mc_next = txn->tw.cursors[dbi];
    txn->tw.cursors[dbi] = &cx.outer;
  
    /* LY: support for update (explicit overwrite) */
    if (flags & MDBX_CURRENT) {
      rc = mdbx_cursor_get(&cx.outer, (MDBX_val *)key, NULL, MDBX_SET);
      if (likely(rc == MDBX_SUCCESS) &&
          (txn->mt_dbs[dbi].md_flags & MDBX_DUPSORT) &&
          (flags & MDBX_ALLDUPS) == 0) {
        /* LY: allows update (explicit overwrite) only for unique keys */
        MDBX_node *node = page_node(cx.outer.mc_pg[cx.outer.mc_top],
                                    cx.outer.mc_ki[cx.outer.mc_top]);
        if (F_ISSET(node_flags(node), F_DUPDATA)) {
          mdbx_tassert(txn, XCURSOR_INITED(&cx.outer) &&
                                cx.outer.mc_xcursor->mx_db.md_entries > 1);
          rc = MDBX_EMULTIVAL;
        }
      }
    }
  
    if (likely(rc == MDBX_SUCCESS))
      rc = mdbx_cursor_put(&cx.outer, key, data, flags);
    txn->tw.cursors[dbi] = cx.outer.mc_next;
  
    return rc;
  }
  
  /**** COPYING *****************************************************************/
  
  #ifndef MDBX_WBUF
  #define MDBX_WBUF ((size_t)1024 * 1024)
  #endif
  
  /* State needed for a double-buffering compacting copy. */
  typedef struct mdbx_copy {
    MDBX_env *mc_env;
    MDBX_txn *mc_txn;
    mdbx_condpair_t mc_condpair;
    uint8_t *mc_wbuf[2];
    uint8_t *mc_over[2];
    size_t mc_wlen[2];
    size_t mc_olen[2];
    mdbx_filehandle_t mc_fd;
    /* Error code.  Never cleared if set.  Both threads can set nonzero
     * to fail the copy.  Not mutex-protected, MDBX expects atomic int. */
    volatile int mc_error;
    pgno_t mc_next_pgno;
    volatile unsigned mc_head;
    volatile unsigned mc_tail;
  } mdbx_copy;
  
  /* Dedicated writer thread for compacting copy. */
  static THREAD_RESULT __cold THREAD_CALL mdbx_env_copythr(void *arg) {
    mdbx_copy *my = arg;
  
  #if defined(EPIPE) && !(defined(_WIN32) || defined(_WIN64))
    sigset_t sigset;
    sigemptyset(&sigset);
    sigaddset(&sigset, SIGPIPE);
    my->mc_error = pthread_sigmask(SIG_BLOCK, &sigset, NULL);
  #endif /* EPIPE */
  
    mdbx_condpair_lock(&my->mc_condpair);
    while (!my->mc_error) {
      while (my->mc_tail == my->mc_head && !my->mc_error) {
        int err = mdbx_condpair_wait(&my->mc_condpair, true);
        if (err != MDBX_SUCCESS) {
          my->mc_error = err;
          goto bailout;
        }
      }
      const unsigned toggle = my->mc_tail & 1;
      size_t wsize = my->mc_wlen[toggle];
      if (wsize == 0) {
        my->mc_tail += 1;
        break /* EOF */;
      }
      my->mc_wlen[toggle] = 0;
      uint8_t *ptr = my->mc_wbuf[toggle];
    again:
      if (!my->mc_error) {
        int err = mdbx_write(my->mc_fd, ptr, wsize);
        if (err != MDBX_SUCCESS) {
  #if defined(EPIPE) && !(defined(_WIN32) || defined(_WIN64))
          if (err == EPIPE) {
            /* Collect the pending SIGPIPE,
             * otherwise at least OS X gives it to the process on thread-exit. */
            int unused;
            sigwait(&sigset, &unused);
          }
  #endif /* EPIPE */
          my->mc_error = err;
          goto bailout;
        }
      }
  
      /* If there's an overflow page tail, write it too */
      wsize = my->mc_olen[toggle];
      if (wsize) {
        my->mc_olen[toggle] = 0;
        ptr = my->mc_over[toggle];
        goto again;
      }
      my->mc_tail += 1;
      mdbx_condpair_signal(&my->mc_condpair, false);
    }
  bailout:
    mdbx_condpair_unlock(&my->mc_condpair);
    return (THREAD_RESULT)0;
  }
  
  /* Give buffer and/or MDBX_EOF to writer thread, await unused buffer. */
  static __cold int mdbx_env_cthr_toggle(mdbx_copy *my) {
    mdbx_condpair_lock(&my->mc_condpair);
    mdbx_assert(my->mc_env, my->mc_head - my->mc_tail < 2 || my->mc_error);
    my->mc_head += 1;
    mdbx_condpair_signal(&my->mc_condpair, true);
    while (!my->mc_error &&
           my->mc_head - my->mc_tail == 2 /* both buffers in use */) {
      int err = mdbx_condpair_wait(&my->mc_condpair, false);
      if (err != MDBX_SUCCESS)
        my->mc_error = err;
    }
    mdbx_condpair_unlock(&my->mc_condpair);
    return my->mc_error;
  }
  
  /* Depth-first tree traversal for compacting copy.
   * [in] my control structure.
   * [in,out] pg database root.
   * [in] flags includes F_DUPDATA if it is a sorted-duplicate sub-DB. */
  static __cold int mdbx_env_cwalk(mdbx_copy *my, pgno_t *pg, int flags) {
    MDBX_cursor_couple couple;
    MDBX_page *mo, *mp, *leaf;
    char *buf, *ptr;
    int rc;
    unsigned i;
  
    /* Empty DB, nothing to do */
    if (*pg == P_INVALID)
      return MDBX_SUCCESS;
  
    memset(&couple, 0, sizeof(couple));
    couple.outer.mc_snum = 1;
    couple.outer.mc_txn = my->mc_txn;
    couple.outer.mc_flags = couple.inner.mx_cursor.mc_flags =
        C_COPYING | C_SKIPORD;
  
    rc = mdbx_page_get(&couple.outer, *pg, &couple.outer.mc_pg[0], NULL,
                       my->mc_txn->mt_txnid);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
    rc = mdbx_page_search_root(&couple.outer, NULL, MDBX_PS_FIRST);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    /* Make cursor pages writable */
    buf = ptr = mdbx_malloc(pgno2bytes(my->mc_env, couple.outer.mc_snum));
    if (buf == NULL)
      return MDBX_ENOMEM;
  
    for (i = 0; i < couple.outer.mc_top; i++) {
      mdbx_page_copy((MDBX_page *)ptr, couple.outer.mc_pg[i],
                     my->mc_env->me_psize);
      couple.outer.mc_pg[i] = (MDBX_page *)ptr;
      ptr += my->mc_env->me_psize;
    }
  
    /* This is writable space for a leaf page. Usually not needed. */
    leaf = (MDBX_page *)ptr;
  
    while (couple.outer.mc_snum > 0) {
      mp = couple.outer.mc_pg[couple.outer.mc_top];
      unsigned n = page_numkeys(mp);
  
      if (IS_LEAF(mp)) {
        if (!IS_LEAF2(mp) && !(flags & F_DUPDATA)) {
          for (i = 0; i < n; i++) {
            MDBX_node *node = page_node(mp, i);
            if (node_flags(node) & F_BIGDATA) {
              MDBX_page *omp;
  
              /* Need writable leaf */
              if (mp != leaf) {
                couple.outer.mc_pg[couple.outer.mc_top] = leaf;
                mdbx_page_copy(leaf, mp, my->mc_env->me_psize);
                mp = leaf;
                node = page_node(mp, i);
              }
  
              const pgno_t pgno = node_largedata_pgno(node);
              poke_pgno(node_data(node), my->mc_next_pgno);
              rc = mdbx_page_get(&couple.outer, pgno, &omp, NULL,
                                 pp_txnid4chk(mp, my->mc_txn));
              if (unlikely(rc != MDBX_SUCCESS))
                goto done;
              unsigned toggle = my->mc_head & 1;
              if (my->mc_wlen[toggle] + my->mc_env->me_psize > MDBX_WBUF) {
                rc = mdbx_env_cthr_toggle(my);
                if (unlikely(rc != MDBX_SUCCESS))
                  goto done;
                toggle = my->mc_head & 1;
              }
              mo = (MDBX_page *)(my->mc_wbuf[toggle] + my->mc_wlen[toggle]);
              memcpy(mo, omp, my->mc_env->me_psize);
              mo->mp_pgno = my->mc_next_pgno;
              my->mc_next_pgno += omp->mp_pages;
              my->mc_wlen[toggle] += my->mc_env->me_psize;
              if (omp->mp_pages > 1) {
                my->mc_olen[toggle] = pgno2bytes(my->mc_env, omp->mp_pages - 1);
                my->mc_over[toggle] = (uint8_t *)omp + my->mc_env->me_psize;
                rc = mdbx_env_cthr_toggle(my);
                if (unlikely(rc != MDBX_SUCCESS))
                  goto done;
                toggle = my->mc_head & 1;
              }
            } else if (node_flags(node) & F_SUBDATA) {
              if (node_ds(node) != sizeof(MDBX_db)) {
                rc = MDBX_CORRUPTED;
                goto done;
              }
  
              /* Need writable leaf */
              if (mp != leaf) {
                couple.outer.mc_pg[couple.outer.mc_top] = leaf;
                mdbx_page_copy(leaf, mp, my->mc_env->me_psize);
                mp = leaf;
                node = page_node(mp, i);
              }
  
              MDBX_db db;
              memcpy(&db, node_data(node), sizeof(MDBX_db));
              rc = mdbx_env_cwalk(my, &db.md_root, node_flags(node) & F_DUPDATA);
              if (rc)
                goto done;
              memcpy(node_data(node), &db, sizeof(MDBX_db));
            }
          }
        }
      } else {
        couple.outer.mc_ki[couple.outer.mc_top]++;
        if (couple.outer.mc_ki[couple.outer.mc_top] < n) {
        again:
          rc = mdbx_page_get(
              &couple.outer,
              node_pgno(page_node(mp, couple.outer.mc_ki[couple.outer.mc_top])),
              &mp, NULL, pp_txnid4chk(mp, my->mc_txn));
          if (unlikely(rc != MDBX_SUCCESS))
            goto done;
          couple.outer.mc_top++;
          couple.outer.mc_snum++;
          couple.outer.mc_ki[couple.outer.mc_top] = 0;
          if (IS_BRANCH(mp)) {
            /* Whenever we advance to a sibling branch page,
             * we must proceed all the way down to its first leaf. */
            mdbx_page_copy(couple.outer.mc_pg[couple.outer.mc_top], mp,
                           my->mc_env->me_psize);
            goto again;
          } else
            couple.outer.mc_pg[couple.outer.mc_top] = mp;
          continue;
        }
      }
      unsigned toggle = my->mc_head & 1;
      if (my->mc_wlen[toggle] + my->mc_wlen[toggle] > MDBX_WBUF) {
        rc = mdbx_env_cthr_toggle(my);
        if (unlikely(rc != MDBX_SUCCESS))
          goto done;
        toggle = my->mc_head & 1;
      }
      mo = (MDBX_page *)(my->mc_wbuf[toggle] + my->mc_wlen[toggle]);
      mdbx_page_copy(mo, mp, my->mc_env->me_psize);
      mo->mp_pgno = my->mc_next_pgno++;
      my->mc_wlen[toggle] += my->mc_env->me_psize;
      if (couple.outer.mc_top) {
        /* Update parent if there is one */
        node_set_pgno(page_node(couple.outer.mc_pg[couple.outer.mc_top - 1],
                                couple.outer.mc_ki[couple.outer.mc_top - 1]),
                      mo->mp_pgno);
        mdbx_cursor_pop(&couple.outer);
      } else {
        /* Otherwise we're done */
        *pg = mo->mp_pgno;
        break;
      }
    }
  done:
    mdbx_free(buf);
    return rc;
  }
  
  static __cold void compact_fixup_meta(MDBX_env *env, MDBX_meta *meta) {
    /* Calculate filesize taking in account shrink/growing thresholds */
    if (meta->mm_geo.next != meta->mm_geo.now) {
      meta->mm_geo.now = meta->mm_geo.next;
      const pgno_t aligner =
          meta->mm_geo.grow ? meta->mm_geo.grow : meta->mm_geo.shrink;
      if (aligner) {
        const pgno_t aligned = pgno_align2os_pgno(
            env, meta->mm_geo.next + aligner - meta->mm_geo.next % aligner);
        meta->mm_geo.now = aligned;
      }
    }
  
    if (meta->mm_geo.now < meta->mm_geo.lower)
      meta->mm_geo.now = meta->mm_geo.lower;
    if (meta->mm_geo.now > meta->mm_geo.upper)
      meta->mm_geo.now = meta->mm_geo.upper;
  
    /* Update signature */
    assert(meta->mm_geo.now >= meta->mm_geo.next);
    meta->mm_datasync_sign = mdbx_meta_sign(meta);
  }
  
  /* Make resizeable */
  static __cold void make_sizeable(MDBX_meta *meta) {
    meta->mm_geo.lower = MIN_PAGENO;
    if (meta->mm_geo.grow == 0) {
      const size_t step = 1 + (meta->mm_geo.upper - meta->mm_geo.lower) / 42;
      meta->mm_geo.grow = (step < UINT16_MAX) ? (uint16_t)step : UINT16_MAX;
    }
    if (meta->mm_geo.shrink == 0) {
      const size_t step = meta->mm_geo.grow + meta->mm_geo.grow;
      meta->mm_geo.shrink = (step < UINT16_MAX) ? (uint16_t)step : UINT16_MAX;
    }
  }
  
  /* Copy environment with compaction. */
  static __cold int mdbx_env_compact(MDBX_env *env, MDBX_txn *read_txn,
                                     mdbx_filehandle_t fd, uint8_t *buffer,
                                     const bool dest_is_pipe, const int flags) {
    const size_t meta_bytes = pgno2bytes(env, NUM_METAS);
    uint8_t *const data_buffer =
        buffer + ceil_powerof2(meta_bytes, env->me_os_psize);
    MDBX_meta *const meta = mdbx_init_metas(env, buffer);
    mdbx_meta_set_txnid(env, meta, read_txn->mt_txnid);
  
    if (flags & MDBX_CP_FORCE_DYNAMIC_SIZE)
      make_sizeable(meta);
  
    /* copy canary sequences if present */
    if (read_txn->mt_canary.v) {
      meta->mm_canary = read_txn->mt_canary;
      meta->mm_canary.v = mdbx_meta_txnid_stable(env, meta);
    }
  
    /* Set metapage 1 with current main DB */
    pgno_t new_root, root = read_txn->mt_dbs[MAIN_DBI].md_root;
    if ((new_root = root) == P_INVALID) {
      /* When the DB is empty, handle it specially to
       * fix any breakage like page leaks from ITS#8174. */
      meta->mm_dbs[MAIN_DBI].md_flags = read_txn->mt_dbs[MAIN_DBI].md_flags;
      compact_fixup_meta(env, meta);
      if (dest_is_pipe) {
        int rc = mdbx_write(fd, buffer, meta_bytes);
        if (rc != MDBX_SUCCESS)
          return rc;
      }
    } else {
      /* Count free pages + GC pages.  Subtract from last_pg
       * to find the new last_pg, which also becomes the new root. */
      pgno_t freecount = 0;
      MDBX_cursor_couple couple;
      MDBX_val key, data;
  
      int rc = mdbx_cursor_init(&couple.outer, read_txn, FREE_DBI);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      while ((rc = mdbx_cursor_get(&couple.outer, &key, &data, MDBX_NEXT)) == 0)
        freecount += *(pgno_t *)data.iov_base;
      if (unlikely(rc != MDBX_NOTFOUND))
        return rc;
  
      freecount += read_txn->mt_dbs[FREE_DBI].md_branch_pages +
                   read_txn->mt_dbs[FREE_DBI].md_leaf_pages +
                   read_txn->mt_dbs[FREE_DBI].md_overflow_pages;
  
      new_root = read_txn->mt_next_pgno - 1 - freecount;
      meta->mm_geo.next = new_root + 1;
      meta->mm_dbs[MAIN_DBI] = read_txn->mt_dbs[MAIN_DBI];
      meta->mm_dbs[MAIN_DBI].md_root = new_root;
  
      mdbx_copy ctx;
      memset(&ctx, 0, sizeof(ctx));
      rc = mdbx_condpair_init(&ctx.mc_condpair);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
  
      memset(data_buffer, 0, MDBX_WBUF * 2);
      ctx.mc_wbuf[0] = data_buffer;
      ctx.mc_wbuf[1] = data_buffer + MDBX_WBUF;
      ctx.mc_next_pgno = NUM_METAS;
      ctx.mc_env = env;
      ctx.mc_fd = fd;
      ctx.mc_txn = read_txn;
  
      mdbx_thread_t thread;
      int thread_err = mdbx_thread_create(&thread, mdbx_env_copythr, &ctx);
      if (likely(thread_err == MDBX_SUCCESS)) {
        if (dest_is_pipe) {
          compact_fixup_meta(env, meta);
          rc = mdbx_write(fd, buffer, meta_bytes);
        }
        if (rc == MDBX_SUCCESS)
          rc = mdbx_env_cwalk(&ctx, &root, 0);
        mdbx_env_cthr_toggle(&ctx);
        mdbx_env_cthr_toggle(&ctx);
        thread_err = mdbx_thread_join(thread);
        mdbx_assert(env, (ctx.mc_tail == ctx.mc_head &&
                          ctx.mc_wlen[ctx.mc_head & 1] == 0) ||
                             ctx.mc_error);
        mdbx_condpair_destroy(&ctx.mc_condpair);
      }
      if (unlikely(thread_err != MDBX_SUCCESS))
        return thread_err;
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      if (unlikely(ctx.mc_error != MDBX_SUCCESS))
        return ctx.mc_error;
  
      if (dest_is_pipe) {
        if (root != new_root) {
          mdbx_error("post-compactification root %" PRIaPGNO
                     " NE expected %" PRIaPGNO
                     " (source DB corrupted or has a page leak(s))",
                     root, new_root);
          return MDBX_CORRUPTED; /* page leak or corrupt DB */
        }
      } else {
        if (root > new_root) {
          mdbx_error("post-compactification root %" PRIaPGNO
                     " GT expected %" PRIaPGNO " (source DB corrupted)",
                     root, new_root);
          return MDBX_CORRUPTED; /* page leak or corrupt DB */
        }
        if (root < new_root) {
          mdbx_warning("post-compactification root %" PRIaPGNO
                       " LT expected %" PRIaPGNO " (page leak(s) in source DB)",
                       root, new_root);
          /* fixup meta */
          meta->mm_dbs[MAIN_DBI].md_root = root;
          meta->mm_geo.next = root + 1;
        }
        compact_fixup_meta(env, meta);
      }
    }
  
    /* Extend file if required */
    if (meta->mm_geo.now != meta->mm_geo.next) {
      const size_t whole_size = pgno2bytes(env, meta->mm_geo.now);
      if (!dest_is_pipe)
        return mdbx_ftruncate(fd, whole_size);
  
      const size_t used_size = pgno2bytes(env, meta->mm_geo.next);
      memset(data_buffer, 0, MDBX_WBUF);
      for (size_t offset = used_size; offset < whole_size;) {
        const size_t chunk =
            (MDBX_WBUF < whole_size - offset) ? MDBX_WBUF : whole_size - offset;
        /* copy to avoid EFAULT in case swapped-out */
        int rc = mdbx_write(fd, data_buffer, chunk);
        if (unlikely(rc != MDBX_SUCCESS))
          return rc;
        offset += chunk;
      }
    }
    return MDBX_SUCCESS;
  }
  
  /* Copy environment as-is. */
  static __cold int mdbx_env_copy_asis(MDBX_env *env, MDBX_txn *read_txn,
                                       mdbx_filehandle_t fd, uint8_t *buffer,
                                       const bool dest_is_pipe, const int flags) {
    /* We must start the actual read txn after blocking writers */
    int rc = mdbx_txn_end(read_txn, MDBX_END_RESET_TMP);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    /* Temporarily block writers until we snapshot the meta pages */
    rc = mdbx_txn_lock(env, false);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    rc = mdbx_txn_renew0(read_txn, MDBX_TXN_RDONLY);
    if (unlikely(rc != MDBX_SUCCESS)) {
      mdbx_txn_unlock(env);
      return rc;
    }
  
    mdbx_jitter4testing(false);
    const size_t meta_bytes = pgno2bytes(env, NUM_METAS);
    /* Make a snapshot of meta-pages,
     * but writing ones after the data was flushed */
    memcpy(buffer, env->me_map, meta_bytes);
    MDBX_meta *const headcopy = /* LY: get pointer to the snapshot copy */
        (MDBX_meta *)(buffer + ((uint8_t *)mdbx_meta_head(env) - env->me_map));
    mdbx_txn_unlock(env);
  
    if (flags & MDBX_CP_FORCE_DYNAMIC_SIZE)
      make_sizeable(headcopy);
    /* Update signature to steady */
    headcopy->mm_datasync_sign = mdbx_meta_sign(headcopy);
  
    /* Copy the data */
    const size_t whole_size = pgno_align2os_bytes(env, read_txn->mt_end_pgno);
    const size_t used_size = pgno2bytes(env, read_txn->mt_next_pgno);
    mdbx_jitter4testing(false);
  
    if (dest_is_pipe)
      rc = mdbx_write(fd, buffer, meta_bytes);
  
    uint8_t *const data_buffer =
        buffer + ceil_powerof2(meta_bytes, env->me_os_psize);
    for (size_t offset = meta_bytes; rc == MDBX_SUCCESS && offset < used_size;) {
  #if MDBX_USE_SENDFILE
      static bool sendfile_unavailable;
      if (dest_is_pipe && likely(!sendfile_unavailable)) {
        off_t in_offset = offset;
        const ssize_t written =
            sendfile(fd, env->me_lazy_fd, &in_offset, used_size - offset);
        if (likely(written > 0)) {
          offset = in_offset;
          continue;
        }
        rc = MDBX_ENODATA;
        if (written == 0 || ignore_enosys(rc = errno) != MDBX_RESULT_TRUE)
          break;
        sendfile_unavailable = true;
      }
  #endif /* MDBX_USE_SENDFILE */
  
  #if MDBX_USE_COPYFILERANGE
      static bool copyfilerange_unavailable;
      if (!dest_is_pipe && likely(!copyfilerange_unavailable)) {
        off_t in_offset = offset, out_offset = offset;
        ssize_t bytes_copied = copy_file_range(
            env->me_lazy_fd, &in_offset, fd, &out_offset, used_size - offset, 0);
        if (likely(bytes_copied > 0)) {
          offset = in_offset;
          continue;
        }
        rc = MDBX_ENODATA;
        if (bytes_copied == 0 || ignore_enosys(rc = errno) != MDBX_RESULT_TRUE)
          break;
        copyfilerange_unavailable = true;
      }
  #endif /* MDBX_USE_COPYFILERANGE */
  
      /* fallback to portable */
      const size_t chunk =
          (MDBX_WBUF < used_size - offset) ? MDBX_WBUF : used_size - offset;
      /* copy to avoid EFAULT in case swapped-out */
      memcpy(data_buffer, env->me_map + offset, chunk);
      rc = mdbx_write(fd, data_buffer, chunk);
      offset += chunk;
    }
  
    /* Extend file if required */
    if (likely(rc == MDBX_SUCCESS) && whole_size != used_size) {
      if (!dest_is_pipe)
        rc = mdbx_ftruncate(fd, whole_size);
      else {
        memset(data_buffer, 0, MDBX_WBUF);
        for (size_t offset = used_size;
             rc == MDBX_SUCCESS && offset < whole_size;) {
          const size_t chunk =
              (MDBX_WBUF < whole_size - offset) ? MDBX_WBUF : whole_size - offset;
          /* copy to avoid EFAULT in case swapped-out */
          rc = mdbx_write(fd, data_buffer, chunk);
          offset += chunk;
        }
      }
    }
  
    return rc;
  }
  
  __cold int mdbx_env_copy2fd(MDBX_env *env, mdbx_filehandle_t fd,
                              unsigned flags) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    const int dest_is_pipe = mdbx_is_pipe(fd);
    if (MDBX_IS_ERROR(dest_is_pipe))
      return dest_is_pipe;
  
    if (!dest_is_pipe) {
      rc = mdbx_fseek(fd, 0);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  
    const size_t buffer_size =
        pgno_align2os_bytes(env, NUM_METAS) +
        ceil_powerof2(((flags & MDBX_CP_COMPACT) ? MDBX_WBUF * 2 : MDBX_WBUF),
                      env->me_os_psize);
  
    uint8_t *buffer = NULL;
    rc = mdbx_memalign_alloc(env->me_os_psize, buffer_size, (void **)&buffer);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    MDBX_txn *read_txn = NULL;
    /* Do the lock/unlock of the reader mutex before starting the
     * write txn. Otherwise other read txns could block writers. */
    rc = mdbx_txn_begin(env, NULL, MDBX_TXN_RDONLY, &read_txn);
    if (unlikely(rc != MDBX_SUCCESS)) {
      mdbx_memalign_free(buffer);
      return rc;
    }
  
    if (!dest_is_pipe) {
      /* Firstly write a stub to meta-pages.
       * Now we sure to incomplete copy will not be used. */
      memset(buffer, -1, pgno2bytes(env, NUM_METAS));
      rc = mdbx_write(fd, buffer, pgno2bytes(env, NUM_METAS));
    }
  
    if (likely(rc == MDBX_SUCCESS)) {
      memset(buffer, 0, pgno2bytes(env, NUM_METAS));
      rc = ((flags & MDBX_CP_COMPACT) ? mdbx_env_compact : mdbx_env_copy_asis)(
          env, read_txn, fd, buffer, dest_is_pipe, flags);
    }
    mdbx_txn_abort(read_txn);
  
    if (!dest_is_pipe) {
      if (likely(rc == MDBX_SUCCESS))
        rc = mdbx_fsync(fd, MDBX_SYNC_DATA | MDBX_SYNC_SIZE);
  
      /* Write actual meta */
      if (likely(rc == MDBX_SUCCESS))
        rc = mdbx_pwrite(fd, buffer, pgno2bytes(env, NUM_METAS), 0);
  
      if (likely(rc == MDBX_SUCCESS))
        rc = mdbx_fsync(fd, MDBX_SYNC_DATA | MDBX_SYNC_IODQ);
    }
  
    mdbx_memalign_free(buffer);
    return rc;
  }
  
  __cold int mdbx_env_copy(MDBX_env *env, const char *dest_path,
                           MDBX_copy_flags_t flags) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!dest_path))
      return MDBX_EINVAL;
  
    /* The destination path must exist, but the destination file must not.
     * We don't want the OS to cache the writes, since the source data is
     * already in the OS cache. */
    mdbx_filehandle_t newfd;
    rc = mdbx_openfile(MDBX_OPEN_COPY, env, dest_path, &newfd,
  #if defined(_WIN32) || defined(_WIN64)
                       (mdbx_mode_t)-1
  #else
                       S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP
  #endif
    );
  
    if (rc == MDBX_SUCCESS) {
  #if defined(_WIN32) || defined(_WIN64)
      OVERLAPPED ov;
      memset(&ov, 0, sizeof(ov));
      if (!LockFileEx(newfd, LOCKFILE_EXCLUSIVE_LOCK | LOCKFILE_FAIL_IMMEDIATELY,
                      0, 0, INT32_MAX, &ov))
        rc = GetLastError();
  #else
      struct flock lock_op;
      memset(&lock_op, 0, sizeof(lock_op));
      lock_op.l_type = F_WRLCK;
      lock_op.l_whence = SEEK_SET;
      lock_op.l_start = 0;
      lock_op.l_len =
          (sizeof(lock_op.l_len) > 4 ? INT64_MAX : INT32_MAX) & ~(size_t)0xffff;
      if (fcntl(newfd, F_SETLK, &lock_op)
  #if (defined(__linux__) || defined(__gnu_linux__)) && defined(LOCK_EX) &&      \
      (!defined(__ANDROID_API__) || __ANDROID_API__ >= 24)
          || flock(newfd, LOCK_EX | LOCK_NB)
  #endif /* Linux */
      )
        rc = errno;
  #endif /* Windows / POSIX */
    }
  
    if (rc == MDBX_SUCCESS)
      rc = mdbx_env_copy2fd(env, newfd, flags);
  
    if (newfd != INVALID_HANDLE_VALUE) {
      int err = mdbx_closefile(newfd);
      if (rc == MDBX_SUCCESS && err != rc)
        rc = err;
      if (rc != MDBX_SUCCESS)
        (void)mdbx_removefile(dest_path);
    }
  
    return rc;
  }
  
  /******************************************************************************/
  
  __cold int mdbx_env_set_flags(MDBX_env *env, MDBX_env_flags_t flags,
                                bool onoff) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(flags & ~ENV_CHANGEABLE_FLAGS))
      return MDBX_EPERM;
  
    if (unlikely(env->me_flags & MDBX_RDONLY))
      return MDBX_EACCESS;
  
    if (unlikely(env->me_txn0->mt_owner == mdbx_thread_self()))
      return MDBX_BUSY;
  
    rc = mdbx_txn_lock(env, false);
    if (unlikely(rc))
      return rc;
  
    if (onoff)
      env->me_flags = merge_sync_flags(env->me_flags, flags);
    else
      env->me_flags &= ~flags;
  
    mdbx_txn_unlock(env);
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_env_get_flags(const MDBX_env *env, unsigned *arg) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!arg))
      return MDBX_EINVAL;
  
    *arg = env->me_flags & ENV_USABLE_FLAGS;
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_env_set_userctx(MDBX_env *env, void *ctx) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    env->me_userctx = ctx;
    return MDBX_SUCCESS;
  }
  
  void *__cold mdbx_env_get_userctx(const MDBX_env *env) {
    return env ? env->me_userctx : NULL;
  }
  
  __cold int mdbx_env_set_assert(MDBX_env *env, MDBX_assert_func *func) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
  #if MDBX_DEBUG
    env->me_assert_func = func;
    return MDBX_SUCCESS;
  #else
    (void)func;
    return MDBX_ENOSYS;
  #endif
  }
  
  __cold int mdbx_env_get_path(const MDBX_env *env, const char **arg) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!arg))
      return MDBX_EINVAL;
  
    *arg = env->me_pathname;
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_env_get_fd(const MDBX_env *env, mdbx_filehandle_t *arg) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!arg))
      return MDBX_EINVAL;
  
    *arg = env->me_lazy_fd;
    return MDBX_SUCCESS;
  }
  
  /* Common code for mdbx_dbi_stat() and mdbx_env_stat().
   * [in] env the environment to operate in.
   * [in] db the MDBX_db record containing the stats to return.
   * [out] arg the address of an MDBX_stat structure to receive the stats.
   * Returns 0, this function always succeeds. */
  static void mdbx_stat0(const MDBX_env *env, const MDBX_db *db, MDBX_stat *dest,
                         size_t bytes) {
    dest->ms_psize = env->me_psize;
    dest->ms_depth = db->md_depth;
    dest->ms_branch_pages = db->md_branch_pages;
    dest->ms_leaf_pages = db->md_leaf_pages;
    dest->ms_overflow_pages = db->md_overflow_pages;
    dest->ms_entries = db->md_entries;
    if (likely(bytes >=
               offsetof(MDBX_stat, ms_mod_txnid) + sizeof(dest->ms_mod_txnid)))
      dest->ms_mod_txnid = db->md_mod_txnid;
  }
  
  __cold int mdbx_env_stat(const MDBX_env *env, MDBX_stat *stat, size_t bytes) {
    return __inline_mdbx_env_stat(env, stat, bytes);
  }
  
  __cold int mdbx_env_stat_ex(const MDBX_env *env, const MDBX_txn *txn,
                              MDBX_stat *dest, size_t bytes) {
    if (unlikely((env == NULL && txn == NULL) || dest == NULL))
      return MDBX_EINVAL;
  
    if (txn) {
      int err = check_txn(txn, MDBX_TXN_BLOCKED);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
    }
    if (env) {
      int err = check_env(env);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
      if (txn && unlikely(txn->mt_env != env))
        return MDBX_EINVAL;
    }
  
    const size_t size_before_modtxnid = offsetof(MDBX_stat, ms_mod_txnid);
    if (unlikely(bytes != sizeof(MDBX_stat)) && bytes != size_before_modtxnid)
      return MDBX_EINVAL;
  
    if (txn) {
      mdbx_stat0(txn->mt_env, &txn->mt_dbs[MAIN_DBI], dest, bytes);
      return MDBX_SUCCESS;
    }
  
    while (1) {
      const MDBX_meta *const recent_meta = mdbx_meta_head(env);
      const txnid_t txnid = mdbx_meta_txnid_fluid(env, recent_meta);
      mdbx_stat0(env, &recent_meta->mm_dbs[MAIN_DBI], dest, bytes);
      mdbx_compiler_barrier();
      if (likely(txnid == mdbx_meta_txnid_fluid(env, recent_meta) &&
                 recent_meta == mdbx_meta_head(env)))
        return MDBX_SUCCESS;
    }
  }
  
  __cold int mdbx_dbi_dupsort_depthmask(MDBX_txn *txn, MDBX_dbi dbi,
                                        uint32_t *mask) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!mask))
      return MDBX_EINVAL;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_VALID)))
      return MDBX_BAD_DBI;
  
    MDBX_cursor_couple cx;
    rc = mdbx_cursor_init(&cx.outer, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
    if ((cx.outer.mc_db->md_flags & MDBX_DUPSORT) == 0)
      return MDBX_RESULT_TRUE;
  
    MDBX_val key, data;
    rc = mdbx_cursor_first(&cx.outer, &key, &data);
    *mask = 0;
    while (rc == MDBX_SUCCESS) {
      const MDBX_node *node = page_node(cx.outer.mc_pg[cx.outer.mc_top],
                                        cx.outer.mc_ki[cx.outer.mc_top]);
      const MDBX_db *db = node_data(node);
      const unsigned flags = node_flags(node);
      switch (flags) {
      case F_BIGDATA:
      case 0:
        /* single-value entry, deep = 0 */
        *mask |= 1 << 0;
        break;
      case F_DUPDATA:
        /* single sub-page, deep = 1 */
        *mask |= 1 << 1;
        break;
      case F_DUPDATA | F_SUBDATA:
        /* sub-tree */
        *mask |= 1 << unaligned_peek_u16(1, &db->md_depth);
        break;
      default:
        mdbx_error("wrong node-flags %u", flags);
        return MDBX_CORRUPTED;
      }
      rc = mdbx_cursor_next(&cx.outer, &key, &data, MDBX_NEXT_NODUP);
    }
  
    return (rc == MDBX_NOTFOUND) ? MDBX_SUCCESS : rc;
  }
  
  __cold int mdbx_env_info(const MDBX_env *env, MDBX_envinfo *info,
                           size_t bytes) {
    return __inline_mdbx_env_info(env, info, bytes);
  }
  
  __cold int mdbx_env_info_ex(const MDBX_env *env, const MDBX_txn *txn,
                              MDBX_envinfo *arg, size_t bytes) {
    if (unlikely((env == NULL && txn == NULL) || arg == NULL))
      return MDBX_EINVAL;
  
    if (txn) {
      int err = check_txn(txn, MDBX_TXN_BLOCKED);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
    }
    if (env) {
      int err = check_env(env);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
      if (txn && unlikely(txn->mt_env != env))
        return MDBX_EINVAL;
    } else {
      env = txn->mt_env;
    }
  
    const size_t size_before_bootid = offsetof(MDBX_envinfo, mi_bootid);
    if (unlikely(bytes != sizeof(MDBX_envinfo)) && bytes != size_before_bootid)
      return MDBX_EINVAL;
  
    const MDBX_meta *const meta0 = METAPAGE(env, 0);
    const MDBX_meta *const meta1 = METAPAGE(env, 1);
    const MDBX_meta *const meta2 = METAPAGE(env, 2);
    pgno_t unsynced_pages;
    while (1) {
      if (unlikely(env->me_flags & MDBX_FATAL_ERROR))
        return MDBX_PANIC;
  
      const MDBX_meta *const recent_meta = mdbx_meta_head(env);
      arg->mi_recent_txnid = mdbx_meta_txnid_fluid(env, recent_meta);
      arg->mi_meta0_txnid = mdbx_meta_txnid_fluid(env, meta0);
      arg->mi_meta0_sign = meta0->mm_datasync_sign;
      arg->mi_meta1_txnid = mdbx_meta_txnid_fluid(env, meta1);
      arg->mi_meta1_sign = meta1->mm_datasync_sign;
      arg->mi_meta2_txnid = mdbx_meta_txnid_fluid(env, meta2);
      arg->mi_meta2_sign = meta2->mm_datasync_sign;
      if (likely(bytes > size_before_bootid)) {
        arg->mi_bootid.meta0.x = meta0->mm_bootid.x;
        arg->mi_bootid.meta1.x = meta0->mm_bootid.x;
        arg->mi_bootid.meta2.x = meta0->mm_bootid.x;
        arg->mi_bootid.meta0.y = meta0->mm_bootid.y;
        arg->mi_bootid.meta1.y = meta0->mm_bootid.y;
        arg->mi_bootid.meta2.y = meta0->mm_bootid.y;
      }
  
      const MDBX_meta *txn_meta = recent_meta;
      arg->mi_last_pgno = txn_meta->mm_geo.next - 1;
      arg->mi_geo.current = pgno2bytes(env, txn_meta->mm_geo.now);
      if (txn) {
        arg->mi_last_pgno = txn->mt_next_pgno - 1;
        arg->mi_geo.current = pgno2bytes(env, txn->mt_end_pgno);
  
        const txnid_t wanna_meta_txnid = (txn->mt_flags & MDBX_TXN_RDONLY)
                                             ? txn->mt_txnid
                                             : txn->mt_txnid - MDBX_TXNID_STEP;
        txn_meta = (arg->mi_meta0_txnid == wanna_meta_txnid) ? meta0 : txn_meta;
        txn_meta = (arg->mi_meta1_txnid == wanna_meta_txnid) ? meta1 : txn_meta;
        txn_meta = (arg->mi_meta2_txnid == wanna_meta_txnid) ? meta2 : txn_meta;
      }
      arg->mi_geo.lower = pgno2bytes(env, txn_meta->mm_geo.lower);
      arg->mi_geo.upper = pgno2bytes(env, txn_meta->mm_geo.upper);
      arg->mi_geo.shrink = pgno2bytes(env, txn_meta->mm_geo.shrink);
      arg->mi_geo.grow = pgno2bytes(env, txn_meta->mm_geo.grow);
      unsynced_pages = *env->me_unsynced_pages +
                       (*env->me_meta_sync_txnid != (uint32_t)arg->mi_last_pgno);
  
      arg->mi_mapsize = env->me_dxb_mmap.limit;
      mdbx_compiler_barrier();
      if (likely(arg->mi_meta0_txnid == mdbx_meta_txnid_fluid(env, meta0) &&
                 arg->mi_meta0_sign == meta0->mm_datasync_sign &&
                 arg->mi_meta1_txnid == mdbx_meta_txnid_fluid(env, meta1) &&
                 arg->mi_meta1_sign == meta1->mm_datasync_sign &&
                 arg->mi_meta2_txnid == mdbx_meta_txnid_fluid(env, meta2) &&
                 arg->mi_meta2_sign == meta2->mm_datasync_sign &&
                 recent_meta == mdbx_meta_head(env) &&
                 arg->mi_recent_txnid == mdbx_meta_txnid_fluid(env, recent_meta)))
        break;
    }
  
    arg->mi_maxreaders = env->me_maxreaders;
    arg->mi_numreaders = env->me_lck ? env->me_lck->mti_numreaders : INT32_MAX;
    arg->mi_dxb_pagesize = env->me_psize;
    arg->mi_sys_pagesize = env->me_os_psize;
  
    const MDBX_lockinfo *const lck = env->me_lck;
    if (likely(bytes > size_before_bootid)) {
      arg->mi_unsync_volume = pgno2bytes(env, unsynced_pages);
      const uint64_t monotime_now = mdbx_osal_monotime();
      arg->mi_since_sync_seconds16dot16 =
          mdbx_osal_monotime_to_16dot16(monotime_now - *env->me_sync_timestamp);
      arg->mi_since_reader_check_seconds16dot16 =
          lck ? mdbx_osal_monotime_to_16dot16(monotime_now -
                                              lck->mti_reader_check_timestamp)
              : 0;
      arg->mi_autosync_threshold = pgno2bytes(env, *env->me_autosync_threshold);
      arg->mi_autosync_period_seconds16dot16 =
          mdbx_osal_monotime_to_16dot16(*env->me_autosync_period);
      arg->mi_bootid.current.x = bootid.x;
      arg->mi_bootid.current.y = bootid.y;
      arg->mi_mode = lck ? lck->mti_envmode : env->me_flags;
    }
  
    arg->mi_self_latter_reader_txnid = arg->mi_latter_reader_txnid = 0;
    if (lck) {
      arg->mi_self_latter_reader_txnid = arg->mi_latter_reader_txnid =
          arg->mi_recent_txnid;
      for (unsigned i = 0; i < arg->mi_numreaders; ++i) {
        const uint32_t pid = lck->mti_readers[i].mr_pid;
        if (pid) {
          const txnid_t txnid = safe64_read(&lck->mti_readers[i].mr_txnid);
          if (arg->mi_latter_reader_txnid > txnid)
            arg->mi_latter_reader_txnid = txnid;
          if (pid == env->me_pid && arg->mi_self_latter_reader_txnid > txnid)
            arg->mi_self_latter_reader_txnid = txnid;
        }
      }
    }
  
    return MDBX_SUCCESS;
  }
  
  static __inline MDBX_cmp_func *get_default_keycmp(unsigned flags) {
    return (flags & MDBX_REVERSEKEY)
               ? cmp_reverse
               : (flags & MDBX_INTEGERKEY) ? cmp_int_align2 : cmp_lexical;
  }
  
  static __inline MDBX_cmp_func *get_default_datacmp(unsigned flags) {
    return !(flags & MDBX_DUPSORT)
               ? cmp_lenfast
               : ((flags & MDBX_INTEGERDUP)
                      ? cmp_int_unaligned
                      : ((flags & MDBX_REVERSEDUP) ? cmp_reverse : cmp_lexical));
  }
  
  static int mdbx_dbi_bind(MDBX_txn *txn, const MDBX_dbi dbi, unsigned user_flags,
                           MDBX_cmp_func *keycmp, MDBX_cmp_func *datacmp) {
    /* LY: so, accepting only three cases for the table's flags:
     * 1) user_flags and both comparators are zero
     *    = assume that a by-default mode/flags is requested for reading;
     * 2) user_flags exactly the same
     *    = assume that the target mode/flags are requested properly;
     * 3) user_flags differs, but table is empty and MDBX_CREATE is provided
     *    = assume that a properly create request with custom flags;
     */
    if ((user_flags ^ txn->mt_dbs[dbi].md_flags) & DB_PERSISTENT_FLAGS) {
      /* flags are differs, check other conditions */
      if ((!user_flags && (!keycmp || keycmp == txn->mt_dbxs[dbi].md_cmp) &&
           (!datacmp || datacmp == txn->mt_dbxs[dbi].md_dcmp)) ||
          user_flags == MDBX_ACCEDE) {
        /* no comparators were provided and flags are zero,
         * seems that is case #1 above */
        user_flags = txn->mt_dbs[dbi].md_flags;
      } else if ((user_flags & MDBX_CREATE) && txn->mt_dbs[dbi].md_entries == 0) {
        if (txn->mt_flags & MDBX_TXN_RDONLY)
          return /* FIXME: return extended info */ MDBX_EACCESS;
        /* make sure flags changes get committed */
        txn->mt_dbs[dbi].md_flags = user_flags & DB_PERSISTENT_FLAGS;
        txn->mt_flags |= MDBX_TXN_DIRTY;
      } else {
        return /* FIXME: return extended info */ MDBX_INCOMPATIBLE;
      }
    }
  
    if (!keycmp)
      keycmp = txn->mt_dbxs[dbi].md_cmp ? txn->mt_dbxs[dbi].md_cmp
                                        : get_default_keycmp(user_flags);
    if (txn->mt_dbxs[dbi].md_cmp != keycmp) {
      if (txn->mt_dbxs[dbi].md_cmp)
        return MDBX_EINVAL;
      txn->mt_dbxs[dbi].md_cmp = keycmp;
    }
  
    if (!datacmp)
      datacmp = txn->mt_dbxs[dbi].md_dcmp ? txn->mt_dbxs[dbi].md_dcmp
                                          : get_default_datacmp(user_flags);
    if (txn->mt_dbxs[dbi].md_dcmp != datacmp) {
      if (txn->mt_dbxs[dbi].md_dcmp)
        return MDBX_EINVAL;
      txn->mt_dbxs[dbi].md_dcmp = datacmp;
    }
  
    return MDBX_SUCCESS;
  }
  
  static int dbi_open(MDBX_txn *txn, const char *table_name, unsigned user_flags,
                      MDBX_dbi *dbi, MDBX_cmp_func *keycmp,
                      MDBX_cmp_func *datacmp) {
    int rc = MDBX_EINVAL;
    if (unlikely(!dbi))
      return rc;
  
    if (unlikely((user_flags & ~DB_USABLE_FLAGS) != 0)) {
    early_bailout:
      *dbi = 0;
      return rc;
    }
  
    rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      goto early_bailout;
  
    switch (user_flags & (MDBX_INTEGERDUP | MDBX_DUPFIXED | MDBX_DUPSORT |
                          MDBX_REVERSEDUP | MDBX_ACCEDE)) {
    case MDBX_ACCEDE:
      if ((user_flags & MDBX_CREATE) == 0)
        break;
      __fallthrough /* fall through */;
    default:
      rc = MDBX_EINVAL;
      goto early_bailout;
  
    case MDBX_DUPSORT:
    case MDBX_DUPSORT | MDBX_REVERSEDUP:
    case MDBX_DUPSORT | MDBX_DUPFIXED:
    case MDBX_DUPSORT | MDBX_DUPFIXED | MDBX_REVERSEDUP:
    case MDBX_DUPSORT | MDBX_DUPFIXED | MDBX_INTEGERDUP:
    case MDBX_DUPSORT | MDBX_DUPFIXED | MDBX_INTEGERDUP | MDBX_REVERSEDUP:
    case 0:
      break;
    }
  
    /* main table? */
    if (!table_name) {
      rc = mdbx_dbi_bind(txn, MAIN_DBI, user_flags, keycmp, datacmp);
      if (unlikely(rc != MDBX_SUCCESS))
        goto early_bailout;
      *dbi = MAIN_DBI;
      return rc;
    }
  
    if (txn->mt_dbxs[MAIN_DBI].md_cmp == NULL) {
      txn->mt_dbxs[MAIN_DBI].md_cmp =
          get_default_keycmp(txn->mt_dbs[MAIN_DBI].md_flags);
      txn->mt_dbxs[MAIN_DBI].md_dcmp =
          get_default_datacmp(txn->mt_dbs[MAIN_DBI].md_flags);
    }
  
    /* Is the DB already open? */
    size_t len = strlen(table_name);
    MDBX_dbi scan, slot;
    for (slot = scan = txn->mt_numdbs; --scan >= CORE_DBS;) {
      if (!txn->mt_dbxs[scan].md_name.iov_len) {
        /* Remember this free slot */
        slot = scan;
        continue;
      }
      if (len == txn->mt_dbxs[scan].md_name.iov_len &&
          !strncmp(table_name, txn->mt_dbxs[scan].md_name.iov_base, len)) {
        rc = mdbx_dbi_bind(txn, scan, user_flags, keycmp, datacmp);
        if (unlikely(rc != MDBX_SUCCESS))
          goto early_bailout;
        *dbi = scan;
        return rc;
      }
    }
  
    /* Fail, if no free slot and max hit */
    MDBX_env *env = txn->mt_env;
    if (unlikely(slot >= env->me_maxdbs)) {
      rc = MDBX_DBS_FULL;
      goto early_bailout;
    }
  
    /* Cannot mix named table with some main-table flags */
    if (unlikely(txn->mt_dbs[MAIN_DBI].md_flags &
                 (MDBX_DUPSORT | MDBX_INTEGERKEY))) {
      rc = (user_flags & MDBX_CREATE) ? MDBX_INCOMPATIBLE : MDBX_NOTFOUND;
      goto early_bailout;
    }
  
    /* Find the DB info */
    int exact = 0;
    MDBX_val key, data;
    key.iov_len = len;
    key.iov_base = (void *)table_name;
    MDBX_cursor_couple couple;
    rc = mdbx_cursor_init(&couple.outer, txn, MAIN_DBI);
    if (unlikely(rc != MDBX_SUCCESS))
      goto early_bailout;
    rc = mdbx_cursor_set(&couple.outer, &key, &data, MDBX_SET, &exact);
    if (unlikely(rc != MDBX_SUCCESS)) {
      if (rc != MDBX_NOTFOUND || !(user_flags & MDBX_CREATE))
        goto early_bailout;
    } else {
      /* make sure this is actually a table */
      MDBX_node *node = page_node(couple.outer.mc_pg[couple.outer.mc_top],
                                  couple.outer.mc_ki[couple.outer.mc_top]);
      if (unlikely((node_flags(node) & (F_DUPDATA | F_SUBDATA)) != F_SUBDATA)) {
        rc = MDBX_INCOMPATIBLE;
        goto early_bailout;
      }
      if (unlikely(data.iov_len != sizeof(MDBX_db))) {
        rc = MDBX_CORRUPTED;
        goto early_bailout;
      }
    }
  
    if (rc != MDBX_SUCCESS && unlikely(txn->mt_flags & MDBX_TXN_RDONLY)) {
      rc = MDBX_EACCESS;
      goto early_bailout;
    }
  
    /* Done here so we cannot fail after creating a new DB */
    char *namedup = mdbx_strdup(table_name);
    if (unlikely(!namedup)) {
      rc = MDBX_ENOMEM;
      goto early_bailout;
    }
  
    int err = mdbx_fastmutex_acquire(&env->me_dbi_lock);
    if (unlikely(err != MDBX_SUCCESS)) {
      rc = err;
      mdbx_free(namedup);
      goto early_bailout;
    }
  
    /* Import handles from env */
    dbi_import_locked(txn);
  
    /* Rescan after mutex acquisition & import handles */
    for (slot = scan = txn->mt_numdbs; --scan >= CORE_DBS;) {
      if (!txn->mt_dbxs[scan].md_name.iov_len) {
        /* Remember this free slot */
        slot = scan;
        continue;
      }
      if (len == txn->mt_dbxs[scan].md_name.iov_len &&
          !strncmp(table_name, txn->mt_dbxs[scan].md_name.iov_base, len)) {
        rc = mdbx_dbi_bind(txn, scan, user_flags, keycmp, datacmp);
        if (unlikely(rc != MDBX_SUCCESS))
          goto later_bailout;
        *dbi = scan;
        goto later_exit;
      }
    }
  
    if (unlikely(slot >= env->me_maxdbs)) {
      rc = MDBX_DBS_FULL;
      goto later_bailout;
    }
  
    unsigned dbiflags = DBI_FRESH | DBI_VALID | DBI_USRVALID;
    MDBX_db db_dummy;
    if (unlikely(rc)) {
      /* MDBX_NOTFOUND and MDBX_CREATE: Create new DB */
      mdbx_tassert(txn, rc == MDBX_NOTFOUND);
      memset(&db_dummy, 0, sizeof(db_dummy));
      db_dummy.md_root = P_INVALID;
      db_dummy.md_flags = user_flags & DB_PERSISTENT_FLAGS;
      data.iov_len = sizeof(db_dummy);
      data.iov_base = &db_dummy;
      WITH_CURSOR_TRACKING(couple.outer,
                           rc = mdbx_cursor_put(&couple.outer, &key, &data,
                                                F_SUBDATA | MDBX_NOOVERWRITE));
  
      if (unlikely(rc != MDBX_SUCCESS))
        goto later_bailout;
  
      dbiflags |= DBI_DIRTY | DBI_CREAT;
      txn->mt_flags |= MDBX_TXN_DIRTY;
    }
  
    /* Got info, register DBI in this txn */
    memset(txn->mt_dbxs + slot, 0, sizeof(MDBX_dbx));
    txn->mt_dbs[slot] = *(MDBX_db *)data.iov_base;
    env->me_dbflags[slot] = 0;
    rc = mdbx_dbi_bind(txn, slot, user_flags, keycmp, datacmp);
    if (unlikely(rc != MDBX_SUCCESS)) {
      mdbx_tassert(txn, (dbiflags & DBI_CREAT) == 0);
    later_bailout:
      *dbi = 0;
    later_exit:
      mdbx_free(namedup);
    } else {
      txn->mt_dbistate[slot] = (uint8_t)dbiflags;
      txn->mt_dbxs[slot].md_name.iov_base = namedup;
      txn->mt_dbxs[slot].md_name.iov_len = len;
      txn->mt_dbiseqs[slot] = ++env->me_dbiseqs[slot];
      if (!(dbiflags & DBI_CREAT))
        env->me_dbflags[slot] = txn->mt_dbs[slot].md_flags | DB_VALID;
      if (txn->mt_numdbs == slot) {
        mdbx_compiler_barrier();
        txn->mt_numdbs = env->me_numdbs = slot + 1;
        if (!(txn->mt_flags & MDBX_TXN_RDONLY))
          txn->tw.cursors[slot] = NULL;
      }
      mdbx_assert(env, env->me_numdbs > slot);
      *dbi = slot;
    }
  
    mdbx_ensure(env, mdbx_fastmutex_release(&env->me_dbi_lock) == MDBX_SUCCESS);
    return rc;
  }
  
  int mdbx_dbi_open(MDBX_txn *txn, const char *table_name,
                    MDBX_db_flags_t table_flags, MDBX_dbi *dbi) {
    return dbi_open(txn, table_name, table_flags, dbi, nullptr, nullptr);
  }
  
  int mdbx_dbi_open_ex(MDBX_txn *txn, const char *table_name,
                       MDBX_db_flags_t table_flags, MDBX_dbi *dbi,
                       MDBX_cmp_func *keycmp, MDBX_cmp_func *datacmp) {
    return dbi_open(txn, table_name, table_flags, dbi, keycmp, datacmp);
  }
  
  __cold int mdbx_dbi_stat(MDBX_txn *txn, MDBX_dbi dbi, MDBX_stat *dest,
                           size_t bytes) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!dest))
      return MDBX_EINVAL;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_VALID)))
      return MDBX_BAD_DBI;
  
    const size_t size_before_modtxnid = offsetof(MDBX_stat, ms_mod_txnid);
    if (unlikely(bytes != sizeof(MDBX_stat)) && bytes != size_before_modtxnid)
      return MDBX_EINVAL;
  
    if (unlikely(txn->mt_flags & MDBX_TXN_BLOCKED))
      return MDBX_BAD_TXN;
  
    if (unlikely(txn->mt_dbistate[dbi] & DBI_STALE)) {
      rc = mdbx_fetch_sdb(txn, dbi);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
    mdbx_stat0(txn->mt_env, &txn->mt_dbs[dbi], dest, bytes);
    return MDBX_SUCCESS;
  }
  
  static int mdbx_dbi_close_locked(MDBX_env *env, MDBX_dbi dbi) {
    mdbx_assert(env, dbi >= CORE_DBS);
    if (unlikely(dbi >= env->me_numdbs))
      return MDBX_BAD_DBI;
  
    char *ptr = env->me_dbxs[dbi].md_name.iov_base;
    /* If there was no name, this was already closed */
    if (unlikely(!ptr))
      return MDBX_BAD_DBI;
  
    env->me_dbflags[dbi] = 0;
    env->me_dbiseqs[dbi]++;
    env->me_dbxs[dbi].md_name.iov_len = 0;
    mdbx_compiler_barrier();
    env->me_dbxs[dbi].md_name.iov_base = NULL;
    mdbx_free(ptr);
  
    if (env->me_numdbs == dbi + 1)
      env->me_numdbs = dbi;
  
    return MDBX_SUCCESS;
  }
  
  int mdbx_dbi_close(MDBX_env *env, MDBX_dbi dbi) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(dbi < CORE_DBS || dbi >= env->me_maxdbs))
      return MDBX_BAD_DBI;
  
    rc = mdbx_fastmutex_acquire(&env->me_dbi_lock);
    if (likely(rc == MDBX_SUCCESS)) {
      rc = (dbi < env->me_maxdbs && (env->me_dbflags[dbi] & DB_VALID))
               ? mdbx_dbi_close_locked(env, dbi)
               : MDBX_BAD_DBI;
      mdbx_ensure(env, mdbx_fastmutex_release(&env->me_dbi_lock) == MDBX_SUCCESS);
    }
    return rc;
  }
  
  int mdbx_dbi_flags_ex(MDBX_txn *txn, MDBX_dbi dbi, unsigned *flags,
                        unsigned *state) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!flags || !state))
      return MDBX_EINVAL;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_VALID)))
      return MDBX_BAD_DBI;
  
    *flags = txn->mt_dbs[dbi].md_flags & DB_PERSISTENT_FLAGS;
    *state =
        txn->mt_dbistate[dbi] & (DBI_FRESH | DBI_CREAT | DBI_DIRTY | DBI_STALE);
  
    return MDBX_SUCCESS;
  }
  
  int mdbx_dbi_flags(MDBX_txn *txn, MDBX_dbi dbi, unsigned *flags) {
    return __inline_mdbx_dbi_flags(txn, dbi, flags);
  }
  
  /* Add all the DB's pages to the free list.
   * [in] mc Cursor on the DB to free.
   * [in] subs non-Zero to check for sub-DBs in this DB.
   * Returns 0 on success, non-zero on failure. */
  static int mdbx_drop0(MDBX_cursor *mc, int subs) {
    int rc = mdbx_page_search(mc, NULL, MDBX_PS_FIRST);
    if (likely(rc == MDBX_SUCCESS)) {
      MDBX_txn *txn = mc->mc_txn;
      MDBX_cursor mx;
      unsigned i;
  
      /* DUPSORT sub-DBs have no ovpages/DBs. Omit scanning leaves.
       * This also avoids any P_LEAF2 pages, which have no nodes.
       * Also if the DB doesn't have sub-DBs and has no overflow
       * pages, omit scanning leaves. */
      if ((mc->mc_flags & C_SUB) || (subs | mc->mc_db->md_overflow_pages) == 0)
        mdbx_cursor_pop(mc);
  
      rc = mdbx_pnl_need(&txn->tw.retired_pages,
                         mc->mc_db->md_branch_pages + mc->mc_db->md_leaf_pages +
                             mc->mc_db->md_overflow_pages);
      if (unlikely(rc))
        goto done;
  
      cursor_copy_internal(mc, &mx);
      while (mc->mc_snum > 0) {
        MDBX_page *mp = mc->mc_pg[mc->mc_top];
        unsigned n = page_numkeys(mp);
        if (IS_LEAF(mp)) {
          for (i = 0; i < n; i++) {
            MDBX_node *node = page_node(mp, i);
            if (node_flags(node) & F_BIGDATA) {
              MDBX_page *omp;
              rc = mdbx_page_get(mc, node_largedata_pgno(node), &omp, NULL,
                                 pp_txnid4chk(mp, mc->mc_txn));
              if (unlikely(rc))
                goto done;
              mdbx_cassert(mc, IS_OVERFLOW(omp));
              rc = mdbx_page_retire(mc, omp);
              if (unlikely(rc))
                goto done;
              if (!mc->mc_db->md_overflow_pages && !subs)
                break;
            } else if (subs && (node_flags(node) & F_SUBDATA)) {
              rc = mdbx_xcursor_init1(mc, node, mp);
              if (unlikely(rc != MDBX_SUCCESS))
                goto done;
              rc = mdbx_drop0(&mc->mc_xcursor->mx_cursor, 0);
              if (unlikely(rc))
                goto done;
            }
          }
          if (!subs && !mc->mc_db->md_overflow_pages)
            goto pop;
        } else {
          for (i = 0; i < n; i++) {
            /* free it */
            rc = mdbx_retire_pgno(mc, node_pgno(page_node(mp, i)));
            if (unlikely(rc))
              goto done;
          }
        }
        if (!mc->mc_top)
          break;
        mdbx_cassert(mc, i <= UINT16_MAX);
        mc->mc_ki[mc->mc_top] = (indx_t)i;
        rc = mdbx_cursor_sibling(mc, SIBLING_RIGHT);
        if (rc) {
          if (unlikely(rc != MDBX_NOTFOUND))
            goto done;
        /* no more siblings, go back to beginning
         * of previous level. */
        pop:
          mdbx_cursor_pop(mc);
          mc->mc_ki[0] = 0;
          for (i = 1; i < mc->mc_snum; i++) {
            mc->mc_ki[i] = 0;
            mc->mc_pg[i] = mx.mc_pg[i];
          }
        }
      }
      /* free it */
      rc = mdbx_retire_pgno(mc, mc->mc_db->md_root);
    done:
      if (unlikely(rc))
        txn->mt_flags |= MDBX_TXN_ERROR;
    } else if (rc == MDBX_NOTFOUND) {
      rc = MDBX_SUCCESS;
    }
    mc->mc_flags &= ~C_INITIALIZED;
    return rc;
  }
  
  int mdbx_drop(MDBX_txn *txn, MDBX_dbi dbi, bool del) {
    int rc = check_txn_rw(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    if (unlikely(TXN_DBI_CHANGED(txn, dbi)))
      return MDBX_BAD_DBI;
  
    MDBX_cursor *mc;
    rc = mdbx_cursor_open(txn, dbi, &mc);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID))) {
      rc = MDBX_BAD_DBI;
      goto bailout;
    }
  
    if (unlikely(TXN_DBI_CHANGED(txn, dbi))) {
      rc = MDBX_BAD_DBI;
      goto bailout;
    }
  
    rc = mdbx_drop0(mc, mc->mc_db->md_flags & MDBX_DUPSORT);
    /* Invalidate the dropped DB's cursors */
    for (MDBX_cursor *m2 = txn->tw.cursors[dbi]; m2; m2 = m2->mc_next)
      m2->mc_flags &= ~(C_INITIALIZED | C_EOF);
    if (unlikely(rc))
      goto bailout;
  
    /* Can't delete the main DB */
    if (del && dbi >= CORE_DBS) {
      rc = mdbx_del0(txn, MAIN_DBI, &mc->mc_dbx->md_name, NULL, F_SUBDATA);
      if (likely(rc == MDBX_SUCCESS)) {
        txn->mt_dbistate[dbi] = DBI_STALE;
        MDBX_env *env = txn->mt_env;
        rc = mdbx_fastmutex_acquire(&env->me_dbi_lock);
        if (unlikely(rc != MDBX_SUCCESS)) {
          txn->mt_flags |= MDBX_TXN_ERROR;
          goto bailout;
        }
        mdbx_dbi_close_locked(env, dbi);
        mdbx_ensure(env,
                    mdbx_fastmutex_release(&env->me_dbi_lock) == MDBX_SUCCESS);
      } else {
        txn->mt_flags |= MDBX_TXN_ERROR;
      }
    } else {
      /* reset the DB record, mark it dirty */
      txn->mt_dbistate[dbi] |= DBI_DIRTY;
      txn->mt_dbs[dbi].md_depth = 0;
      txn->mt_dbs[dbi].md_branch_pages = 0;
      txn->mt_dbs[dbi].md_leaf_pages = 0;
      txn->mt_dbs[dbi].md_overflow_pages = 0;
      txn->mt_dbs[dbi].md_entries = 0;
      txn->mt_dbs[dbi].md_root = P_INVALID;
      txn->mt_dbs[dbi].md_seq = 0;
      txn->mt_flags |= MDBX_TXN_DIRTY;
    }
  
  bailout:
    mdbx_cursor_close(mc);
    return rc;
  }
  
  int mdbx_set_compare(MDBX_txn *txn, MDBX_dbi dbi, MDBX_cmp_func *cmp) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    txn->mt_dbxs[dbi].md_cmp = cmp;
    return MDBX_SUCCESS;
  }
  
  int mdbx_set_dupsort(MDBX_txn *txn, MDBX_dbi dbi, MDBX_cmp_func *cmp) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    txn->mt_dbxs[dbi].md_dcmp = cmp;
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_reader_list(const MDBX_env *env, MDBX_reader_list_func *func,
                              void *ctx) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!func))
      return MDBX_EINVAL;
  
    rc = MDBX_RESULT_TRUE;
    int serial = 0;
    if (likely(env->me_lck)) {
      const unsigned snap_nreaders = env->me_lck->mti_numreaders;
      for (unsigned i = 0; i < snap_nreaders; i++) {
        const MDBX_reader *r = env->me_lck->mti_readers + i;
      retry_reader:;
        const uint32_t pid = r->mr_pid;
        if (!pid)
          continue;
        txnid_t txnid = safe64_read(&r->mr_txnid);
        const size_t tid = r->mr_tid;
        const pgno_t pages_used = r->mr_snapshot_pages_used;
        const uint64_t reader_pages_retired = r->mr_snapshot_pages_retired;
        mdbx_compiler_barrier();
        if (unlikely(tid != r->mr_tid ||
                     pages_used != r->mr_snapshot_pages_used ||
                     reader_pages_retired != r->mr_snapshot_pages_retired ||
                     txnid != safe64_read(&r->mr_txnid) || pid != r->mr_pid))
          goto retry_reader;
  
        mdbx_assert(env, txnid > 0);
        if (txnid >= SAFE64_INVALID_THRESHOLD)
          txnid = 0;
  
        size_t bytes_used = 0;
        size_t bytes_retained = 0;
        uint64_t lag = 0;
        if (txnid) {
        retry_header:;
          const MDBX_meta *const recent_meta = mdbx_meta_head(env);
          const uint64_t head_pages_retired = recent_meta->mm_pages_retired;
          const txnid_t head_txnid = mdbx_meta_txnid_fluid(env, recent_meta);
          mdbx_compiler_barrier();
          if (unlikely(recent_meta != mdbx_meta_head(env) ||
                       head_pages_retired != recent_meta->mm_pages_retired) ||
              head_txnid != mdbx_meta_txnid_fluid(env, recent_meta))
            goto retry_header;
  
          lag = (head_txnid - txnid) / MDBX_TXNID_STEP;
          bytes_used = pgno2bytes(env, pages_used);
          bytes_retained = (head_pages_retired > reader_pages_retired)
                               ? pgno2bytes(env, (pgno_t)(head_pages_retired -
                                                          reader_pages_retired))
                               : 0;
        }
        rc = func(ctx, ++serial, i, pid, (mdbx_tid_t)tid, txnid, lag, bytes_used,
                  bytes_retained);
        if (unlikely(rc != MDBX_SUCCESS))
          break;
      }
    }
  
    return rc;
  }
  
  /* Insert pid into list if not already present.
   * return -1 if already present. */
  static bool __cold mdbx_pid_insert(uint32_t *ids, uint32_t pid) {
    /* binary search of pid in list */
    unsigned base = 0;
    unsigned cursor = 1;
    int val = 0;
    unsigned n = ids[0];
  
    while (n > 0) {
      unsigned pivot = n >> 1;
      cursor = base + pivot + 1;
      val = pid - ids[cursor];
  
      if (val < 0) {
        n = pivot;
      } else if (val > 0) {
        base = cursor;
        n -= pivot + 1;
      } else {
        /* found, so it's a duplicate */
        return false;
      }
    }
  
    if (val > 0)
      ++cursor;
  
    ids[0]++;
    for (n = ids[0]; n > cursor; n--)
      ids[n] = ids[n - 1];
    ids[n] = pid;
    return true;
  }
  
  __cold int mdbx_reader_check(MDBX_env *env, int *dead) {
    if (dead)
      *dead = 0;
    return mdbx_cleanup_dead_readers(env, false, dead);
  }
  
  /* Return:
   *  MDBX_RESULT_TRUE - done and mutex recovered
   *  MDBX_SUCCESS     - done
   *  Otherwise errcode. */
  MDBX_INTERNAL_FUNC __cold int
  mdbx_cleanup_dead_readers(MDBX_env *env, int rdt_locked, int *dead) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    mdbx_assert(env, rdt_locked >= 0);
    MDBX_lockinfo *const lck = env->me_lck;
    if (unlikely(lck == NULL)) {
      /* exclusive mode */
      if (dead)
        *dead = 0;
      return MDBX_SUCCESS;
    }
  
    lck->mti_reader_check_timestamp = mdbx_osal_monotime();
    const unsigned snap_nreaders = lck->mti_numreaders;
    uint32_t pidsbuf_onstask[142];
    uint32_t *const pids =
        (snap_nreaders < ARRAY_LENGTH(pidsbuf_onstask))
            ? pidsbuf_onstask
            : mdbx_malloc((snap_nreaders + 1) * sizeof(uint32_t));
    if (unlikely(!pids))
      return MDBX_ENOMEM;
  
    pids[0] = 0;
    int count = 0;
    for (unsigned i = 0; i < snap_nreaders; i++) {
      const uint32_t pid = lck->mti_readers[i].mr_pid;
      if (pid == 0)
        continue /* skip empty */;
      if (pid == env->me_pid)
        continue /* skip self */;
      if (!mdbx_pid_insert(pids, pid))
        continue /* such pid already processed */;
  
      int err = mdbx_rpid_check(env, pid);
      if (err == MDBX_RESULT_TRUE)
        continue /* reader is live */;
  
      if (err != MDBX_SUCCESS) {
        rc = err;
        break /* mdbx_rpid_check() failed */;
      }
  
      /* stale reader found */
      if (!rdt_locked) {
        err = mdbx_rdt_lock(env);
        if (MDBX_IS_ERROR(err)) {
          rc = err;
          break;
        }
  
        rdt_locked = -1;
        if (err == MDBX_RESULT_TRUE) {
          /* mutex recovered, the mdbx_ipclock_failed() checked all readers */
          rc = MDBX_RESULT_TRUE;
          break;
        }
  
        /* a other process may have clean and reused slot, recheck */
        if (lck->mti_readers[i].mr_pid != pid)
          continue;
  
        err = mdbx_rpid_check(env, pid);
        if (MDBX_IS_ERROR(err)) {
          rc = err;
          break;
        }
  
        if (err != MDBX_SUCCESS)
          continue /* the race with other process, slot reused */;
      }
  
      /* clean it */
      for (unsigned j = i; j < snap_nreaders; j++) {
        if (lck->mti_readers[j].mr_pid == pid) {
          mdbx_debug("clear stale reader pid %" PRIuPTR " txn %" PRIaTXN,
                     (size_t)pid, lck->mti_readers[j].mr_txnid.inconsistent);
          lck->mti_readers[j].mr_pid = 0;
          mdbx_compiler_barrier();
          lck->mti_readers_refresh_flag = true;
          count++;
        }
      }
    }
  
    if (rdt_locked < 0)
      mdbx_rdt_unlock(env);
  
    if (pids != pidsbuf_onstask)
      mdbx_free(pids);
  
    if (dead)
      *dead = count;
    return rc;
  }
  
  __cold int mdbx_setup_debug(int loglevel, int flags, MDBX_debug_func *logger) {
    const int rc = mdbx_runtime_flags | (mdbx_loglevel << 16);
  
    if (loglevel != MDBX_LOG_DONTCHANGE)
      mdbx_loglevel = (uint8_t)loglevel;
  
    if (flags != MDBX_DBG_DONTCHANGE) {
      flags &=
  #if MDBX_DEBUG
          MDBX_DBG_ASSERT | MDBX_DBG_AUDIT | MDBX_DBG_JITTER |
  #endif
          MDBX_DBG_DUMP | MDBX_DBG_LEGACY_MULTIOPEN | MDBX_DBG_LEGACY_OVERLAP;
      mdbx_runtime_flags = (uint8_t)flags;
    }
  
    if (logger != MDBX_LOGGER_DONTCHANGE)
      mdbx_debug_logger = logger;
    return rc;
  }
  
  static txnid_t __cold mdbx_kick_longlived_readers(MDBX_env *env,
                                                    const txnid_t laggard) {
    mdbx_debug("DB size maxed out by reading #%" PRIaTXN, laggard);
  
    int retry;
    for (retry = 0; retry < INT_MAX; ++retry) {
      txnid_t oldest = mdbx_recent_steady_txnid(env);
      mdbx_assert(env, oldest < env->me_txn0->mt_txnid);
      mdbx_assert(env, oldest >= laggard);
      mdbx_assert(env, oldest >= *env->me_oldest);
      if (oldest == laggard || unlikely(!env->me_lck /* without-LCK mode */))
        return oldest;
  
      if (MDBX_IS_ERROR(mdbx_cleanup_dead_readers(env, false, NULL)))
        break;
  
      MDBX_reader *asleep = nullptr;
      MDBX_lockinfo *const lck = env->me_lck;
      uint64_t oldest_retired = UINT64_MAX;
      const unsigned snap_nreaders = lck->mti_numreaders;
      for (unsigned i = 0; i < snap_nreaders; ++i) {
      retry:
        if (lck->mti_readers[i].mr_pid) {
          /* mdbx_jitter4testing(true); */
          const uint64_t snap_retired =
              lck->mti_readers[i].mr_snapshot_pages_retired;
          const txnid_t snap_txnid = safe64_read(&lck->mti_readers[i].mr_txnid);
          mdbx_memory_barrier();
          if (unlikely(snap_retired !=
                           lck->mti_readers[i].mr_snapshot_pages_retired ||
                       snap_txnid != safe64_read(&lck->mti_readers[i].mr_txnid)))
            goto retry;
          if (oldest > snap_txnid &&
              laggard <= /* ignore pending updates */ snap_txnid) {
            oldest = snap_txnid;
            oldest_retired = snap_retired;
            asleep = &lck->mti_readers[i];
          }
        }
      }
  
      if (laggard < oldest || !asleep) {
        if (retry && env->me_hsr_callback) {
          /* LY: notify end of hsr-loop */
          const txnid_t gap = oldest - laggard;
          env->me_hsr_callback(env, env->me_txn, 0, 0, laggard,
                               (gap < UINT_MAX) ? (unsigned)gap : UINT_MAX, 0,
                               -retry);
        }
        mdbx_notice("hsr-kick: update oldest %" PRIaTXN " -> %" PRIaTXN,
                    *env->me_oldest, oldest);
        mdbx_assert(env, *env->me_oldest <= oldest);
        return *env->me_oldest = oldest;
      }
  
      if (!env->me_hsr_callback)
        break;
  
      uint32_t pid = asleep->mr_pid;
      size_t tid = asleep->mr_tid;
      if (safe64_read(&asleep->mr_txnid) != laggard || pid <= 0)
        continue;
  
      const MDBX_meta *head_meta = mdbx_meta_head(env);
      const txnid_t gap =
          (mdbx_meta_txnid_stable(env, head_meta) - laggard) / MDBX_TXNID_STEP;
      const uint64_t head_retired = head_meta->mm_pages_retired;
      const size_t space =
          (oldest_retired > head_retired)
              ? pgno2bytes(env, (pgno_t)(oldest_retired - head_retired))
              : 0;
      int rc = env->me_hsr_callback(
          env, env->me_txn, pid, (mdbx_tid_t)tid, laggard,
          (gap < UINT_MAX) ? (unsigned)gap : UINT_MAX, space, retry);
      if (rc < 0)
        break;
  
      if (rc > 0) {
        if (rc == 1) {
          safe64_reset_compare(&asleep->mr_txnid, laggard);
        } else {
          safe64_reset(&asleep->mr_txnid, true);
          asleep->mr_tid = 0;
          asleep->mr_pid = 0;
        }
        mdbx_compiler_barrier();
        lck->mti_readers_refresh_flag = true;
        mdbx_flush_incoherent_cpu_writeback();
      }
    }
  
    if (retry && env->me_hsr_callback) {
      /* LY: notify end of hsr-loop */
      env->me_hsr_callback(env, env->me_txn, 0, 0, laggard, 0, 0, -retry);
    }
    return mdbx_find_oldest(env->me_txn);
  }
  
  __cold int mdbx_env_set_syncbytes(MDBX_env *env, size_t threshold) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(env->me_flags & MDBX_RDONLY))
      return MDBX_EACCESS;
  
    if (unlikely(!env->me_map))
      return MDBX_EPERM;
  
    *env->me_autosync_threshold = bytes2pgno(env, threshold + env->me_psize - 1);
    if (threshold) {
      rc = mdbx_env_sync_poll(env);
      if (unlikely(MDBX_IS_ERROR(rc)))
        return rc;
    }
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_env_set_syncperiod(MDBX_env *env, unsigned seconds_16dot16) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(env->me_flags & MDBX_RDONLY))
      return MDBX_EACCESS;
  
    if (unlikely(!env->me_map))
      return MDBX_EPERM;
  
    *env->me_autosync_period = mdbx_osal_16dot16_to_monotime(seconds_16dot16);
    if (seconds_16dot16) {
      rc = mdbx_env_sync_poll(env);
      if (unlikely(MDBX_IS_ERROR(rc)))
        return rc;
    }
    return MDBX_SUCCESS;
  }
  
  __cold int mdbx_env_set_hsr(MDBX_env *env, MDBX_hsr_func *hsr) {
    int rc = check_env(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    env->me_hsr_callback = hsr;
    return MDBX_SUCCESS;
  }
  
  MDBX_hsr_func *__cold mdbx_env_get_hsr(const MDBX_env *env) {
    return likely(env && env->me_signature == MDBX_ME_SIGNATURE)
               ? env->me_hsr_callback
               : NULL;
  }
  
  #ifdef __SANITIZE_THREAD__
  /* LY: avoid tsan-trap by me_txn, mm_last_pg and mt_next_pgno */
  __attribute__((__no_sanitize_thread__, __noinline__))
  #endif
  int mdbx_txn_straggler(const MDBX_txn *txn, int *percent)
  {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return (rc > 0) ? -rc : rc;
  
    MDBX_env *env = txn->mt_env;
    if (unlikely((txn->mt_flags & MDBX_TXN_RDONLY) == 0)) {
      if (percent)
        *percent =
            (int)((txn->mt_next_pgno * UINT64_C(100) + txn->mt_end_pgno / 2) /
                  txn->mt_end_pgno);
      return 0;
    }
  
    txnid_t recent;
    MDBX_meta *meta;
    do {
      meta = mdbx_meta_head(env);
      recent = mdbx_meta_txnid_fluid(env, meta);
      if (percent) {
        const pgno_t maxpg = meta->mm_geo.now;
        *percent = (int)((meta->mm_geo.next * UINT64_C(100) + maxpg / 2) / maxpg);
      }
    } while (unlikely(recent != mdbx_meta_txnid_fluid(env, meta)));
  
    txnid_t lag = (recent - txn->mt_txnid) / MDBX_TXNID_STEP;
    return (lag > INT_MAX) ? INT_MAX : (int)lag;
  }
  
  typedef struct mdbx_walk_ctx {
    void *mw_user;
    MDBX_pgvisitor_func *mw_visitor;
    MDBX_txn *mw_txn;
    MDBX_cursor *mw_cursor;
    bool mw_dont_check_keys_ordering;
  } mdbx_walk_ctx_t;
  
  static __cold int mdbx_walk_sdb(mdbx_walk_ctx_t *ctx, MDBX_db *const db,
                                  const char *name, int deep);
  
  static MDBX_page_type_t walk_page_type(const MDBX_page *mp) {
    if (mp)
      switch (mp->mp_flags) {
      case P_BRANCH:
        return MDBX_page_branch;
      case P_LEAF:
        return MDBX_page_leaf;
      case P_LEAF | P_LEAF2:
        return MDBX_page_dupfixed_leaf;
      case P_OVERFLOW:
        return MDBX_page_large;
      case P_META:
        return MDBX_page_meta;
      }
    return MDBX_page_broken;
  }
  
  /* Depth-first tree traversal. */
  static __cold int mdbx_walk_tree(mdbx_walk_ctx_t *ctx, const pgno_t pgno,
                                   const char *name, int deep,
                                   txnid_t parent_txnid) {
    assert(pgno != P_INVALID);
    MDBX_page *mp = nullptr;
    int rc, err = mdbx_page_get(ctx->mw_cursor, pgno, &mp, NULL, parent_txnid);
    if (err == MDBX_SUCCESS)
      err = mdbx_page_check(ctx->mw_cursor, mp, 0);
  
    MDBX_page_type_t type = walk_page_type(mp);
    const int nentries = (mp && !IS_OVERFLOW(mp)) ? page_numkeys(mp) : 1;
    unsigned npages = (mp && IS_OVERFLOW(mp)) ? mp->mp_pages : 1;
    size_t pagesize = pgno2bytes(ctx->mw_txn->mt_env, npages);
    size_t header_size = (mp && !IS_LEAF2(mp) && !IS_OVERFLOW(mp))
                             ? PAGEHDRSZ + mp->mp_lower
                             : PAGEHDRSZ;
    size_t payload_size = 0;
    size_t unused_size =
        (mp && !IS_OVERFLOW(mp) ? page_room(mp) : pagesize - header_size) -
        payload_size;
    size_t align_bytes = 0;
  
    if (err == MDBX_SUCCESS) {
      /* LY: Don't use mask here, e.g bitwise
       * (P_BRANCH|P_LEAF|P_LEAF2|P_META|P_OVERFLOW|P_SUBP).
       * Pages should not me marked dirty/loose or otherwise. */
      switch (mp->mp_flags) {
      default:
        err = MDBX_CORRUPTED;
        break;
      case P_BRANCH:
        if (unlikely(nentries < 2))
          err = MDBX_CORRUPTED;
      case P_LEAF:
      case P_LEAF | P_LEAF2:
        break;
      }
    }
  
    for (int i = 0; err == MDBX_SUCCESS && i < nentries;
         align_bytes += ((payload_size + align_bytes) & 1), i++) {
      if (type == MDBX_page_dupfixed_leaf) {
        /* LEAF2 pages have no mp_ptrs[] or node headers */
        payload_size += mp->mp_leaf2_ksize;
        continue;
      }
  
      MDBX_node *node = page_node(mp, i);
      payload_size += NODESIZE + node_ks(node);
  
      if (type == MDBX_page_branch) {
        assert(i > 0 || node_ks(node) == 0);
        continue;
      }
  
      assert(type == MDBX_page_leaf);
      switch (node_flags(node)) {
      case 0 /* usual node */:
        payload_size += node_ds(node);
        break;
  
      case F_BIGDATA /* long data on the large/overflow page */: {
        payload_size += sizeof(pgno_t);
        const pgno_t large_pgno = node_largedata_pgno(node);
        const size_t over_payload = node_ds(node);
        const size_t over_header = PAGEHDRSZ;
        npages = 1;
  
        MDBX_page *op;
        err = mdbx_page_get(ctx->mw_cursor, large_pgno, &op, NULL,
                            pp_txnid4chk(mp, ctx->mw_txn));
        if (err == MDBX_SUCCESS)
          err = mdbx_page_check(ctx->mw_cursor, op, 0);
        if (err == MDBX_SUCCESS) {
          /* LY: Don't use mask here, e.g bitwise
           * (P_BRANCH|P_LEAF|P_LEAF2|P_META|P_OVERFLOW|P_SUBP).
           * Pages should not me marked dirty/loose or otherwise. */
          if (P_OVERFLOW != op->mp_flags)
            err = bad_page(mp, "wrong page type %d for large data", op->mp_flags);
          else
            npages = op->mp_pages;
        }
  
        pagesize = pgno2bytes(ctx->mw_txn->mt_env, npages);
        const size_t over_unused = pagesize - over_payload - over_header;
        rc = ctx->mw_visitor(large_pgno, npages, ctx->mw_user, deep, name,
                             pagesize, MDBX_page_large, err, 1, over_payload,
                             over_header, over_unused);
        if (unlikely(rc != MDBX_SUCCESS))
          return (rc == MDBX_RESULT_TRUE) ? MDBX_SUCCESS : rc;
      } break;
  
      case F_SUBDATA /* sub-db */: {
        const size_t namelen = node_ks(node);
        payload_size += node_ds(node);
        if (unlikely(namelen == 0 || node_ds(node) != sizeof(MDBX_db)))
          err = MDBX_CORRUPTED;
      } break;
  
      case F_SUBDATA | F_DUPDATA /* dupsorted sub-tree */:
        payload_size += sizeof(MDBX_db);
        if (unlikely(node_ds(node) != sizeof(MDBX_db)))
          err = MDBX_CORRUPTED;
        break;
  
      case F_DUPDATA /* short sub-page */: {
        if (unlikely(node_ds(node) <= PAGEHDRSZ)) {
          err = MDBX_CORRUPTED;
          break;
        }
  
        MDBX_page *sp = node_data(node);
        const int nsubkeys = page_numkeys(sp);
        size_t subheader_size =
            IS_LEAF2(sp) ? PAGEHDRSZ : PAGEHDRSZ + sp->mp_lower;
        size_t subunused_size = page_room(sp);
        size_t subpayload_size = 0;
        size_t subalign_bytes = 0;
        MDBX_page_type_t subtype;
  
        switch (sp->mp_flags & ~P_DIRTY /* ignore for sub-pages */) {
        case P_LEAF | P_SUBP:
          subtype = MDBX_subpage_leaf;
          break;
        case P_LEAF | P_LEAF2 | P_SUBP:
          subtype = MDBX_subpage_dupfixed_leaf;
          break;
        default:
          subtype = MDBX_subpage_broken;
          err = MDBX_CORRUPTED;
        }
  
        for (int j = 0; err == MDBX_SUCCESS && j < nsubkeys;
             subalign_bytes += ((subpayload_size + subalign_bytes) & 1), j++) {
  
          if (subtype == MDBX_subpage_dupfixed_leaf) {
            /* LEAF2 pages have no mp_ptrs[] or node headers */
            subpayload_size += sp->mp_leaf2_ksize;
          } else {
            assert(subtype == MDBX_subpage_leaf);
            MDBX_node *subnode = page_node(sp, j);
            subpayload_size += NODESIZE + node_ks(subnode) + node_ds(subnode);
            if (unlikely(node_flags(subnode) != 0))
              err = MDBX_CORRUPTED;
          }
        }
  
        rc = ctx->mw_visitor(pgno, 0, ctx->mw_user, deep + 1, name, node_ds(node),
                             subtype, err, nsubkeys, subpayload_size,
                             subheader_size, subunused_size + subalign_bytes);
        if (unlikely(rc != MDBX_SUCCESS))
          return (rc == MDBX_RESULT_TRUE) ? MDBX_SUCCESS : rc;
        header_size += subheader_size;
        unused_size += subunused_size;
        payload_size += subpayload_size;
        align_bytes += subalign_bytes;
      } break;
  
      default:
        err = MDBX_CORRUPTED;
      }
    }
  
    rc = ctx->mw_visitor(pgno, 1, ctx->mw_user, deep, name,
                         ctx->mw_txn->mt_env->me_psize, type, err, nentries,
                         payload_size, header_size, unused_size + align_bytes);
    if (unlikely(rc != MDBX_SUCCESS))
      return (rc == MDBX_RESULT_TRUE) ? MDBX_SUCCESS : rc;
  
    for (int i = 0; err == MDBX_SUCCESS && i < nentries; i++) {
      if (type == MDBX_page_dupfixed_leaf)
        continue;
  
      MDBX_node *node = page_node(mp, i);
      if (type == MDBX_page_branch) {
        err = mdbx_walk_tree(ctx, node_pgno(node), name, deep + 1,
                             pp_txnid4chk(mp, ctx->mw_txn));
        if (unlikely(err != MDBX_SUCCESS)) {
          if (err == MDBX_RESULT_TRUE)
            break;
          return err;
        }
        continue;
      }
  
      assert(type == MDBX_page_leaf);
      MDBX_db db;
      switch (node_flags(node)) {
      default:
        continue;
  
      case F_SUBDATA /* sub-db */: {
        const size_t namelen = node_ks(node);
        if (unlikely(namelen == 0 || node_ds(node) != sizeof(MDBX_db))) {
          err = MDBX_CORRUPTED;
          break;
        }
  
        char namebuf_onstask[64];
        char *const sub_name = (namelen < sizeof(namebuf_onstask))
                                   ? namebuf_onstask
                                   : mdbx_malloc(namelen + 1);
        if (sub_name) {
          memcpy(sub_name, node_key(node), namelen);
          sub_name[namelen] = 0;
          memcpy(&db, node_data(node), sizeof(db));
          err = mdbx_walk_sdb(ctx, &db, sub_name, deep + 1);
          if (sub_name != namebuf_onstask)
            mdbx_free(sub_name);
        } else {
          err = MDBX_ENOMEM;
        }
      } break;
  
      case F_SUBDATA | F_DUPDATA /* dupsorted sub-tree */:
        if (unlikely(node_ds(node) != sizeof(MDBX_db) ||
                     ctx->mw_cursor->mc_xcursor == NULL))
          err = MDBX_CORRUPTED;
        else {
          memcpy(&db, node_data(node), sizeof(db));
          assert(ctx->mw_cursor->mc_xcursor ==
                 &container_of(ctx->mw_cursor, MDBX_cursor_couple, outer)->inner);
          ctx->mw_cursor = &ctx->mw_cursor->mc_xcursor->mx_cursor;
          err = mdbx_walk_tree(ctx, db.md_root, name, deep + 1,
                               pp_txnid4chk(mp, ctx->mw_txn));
          MDBX_xcursor *inner_xcursor =
              container_of(ctx->mw_cursor, MDBX_xcursor, mx_cursor);
          MDBX_cursor_couple *couple =
              container_of(inner_xcursor, MDBX_cursor_couple, inner);
          ctx->mw_cursor = &couple->outer;
        }
        break;
      }
    }
  
    return MDBX_SUCCESS;
  }
  
  static __cold int mdbx_walk_sdb(mdbx_walk_ctx_t *ctx, MDBX_db *const db,
                                  const char *name, int deep) {
    if (unlikely(db->md_root == P_INVALID))
      return MDBX_SUCCESS; /* empty db */
  
    MDBX_cursor_couple couple;
    MDBX_dbx dbx = {.md_klen_min = INT_MAX};
    uint8_t dbistate = DBI_VALID | DBI_AUDITED;
    int rc = mdbx_couple_init(&couple, ~0u, ctx->mw_txn, db, &dbx, &dbistate);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (ctx->mw_dont_check_keys_ordering) {
      couple.outer.mc_flags |= C_SKIPORD;
      couple.inner.mx_cursor.mc_flags |= C_SKIPORD;
    }
    couple.outer.mc_next = ctx->mw_cursor;
    ctx->mw_cursor = &couple.outer;
    rc = mdbx_walk_tree(ctx, db->md_root, name, deep, ctx->mw_txn->mt_txnid);
    ctx->mw_cursor = couple.outer.mc_next;
    return rc;
  }
  
  __cold int mdbx_env_pgwalk(MDBX_txn *txn, MDBX_pgvisitor_func *visitor,
                             void *user, bool dont_check_keys_ordering) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    mdbx_walk_ctx_t ctx;
    memset(&ctx, 0, sizeof(ctx));
    ctx.mw_txn = txn;
    ctx.mw_user = user;
    ctx.mw_visitor = visitor;
    ctx.mw_dont_check_keys_ordering = dont_check_keys_ordering;
  
    rc = visitor(0, NUM_METAS, user, 0, MDBX_PGWALK_META,
                 pgno2bytes(txn->mt_env, NUM_METAS), MDBX_page_meta, MDBX_SUCCESS,
                 NUM_METAS, sizeof(MDBX_meta) * NUM_METAS, PAGEHDRSZ * NUM_METAS,
                 (txn->mt_env->me_psize - sizeof(MDBX_meta) - PAGEHDRSZ) *
                     NUM_METAS);
    if (!MDBX_IS_ERROR(rc))
      rc = mdbx_walk_sdb(&ctx, &txn->mt_dbs[FREE_DBI], MDBX_PGWALK_GC, 0);
    if (!MDBX_IS_ERROR(rc))
      rc = mdbx_walk_sdb(&ctx, &txn->mt_dbs[MAIN_DBI], MDBX_PGWALK_MAIN, 0);
    return rc;
  }
  
  int mdbx_canary_put(MDBX_txn *txn, const MDBX_canary *canary) {
    int rc = check_txn_rw(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (likely(canary)) {
      if (txn->mt_canary.x == canary->x && txn->mt_canary.y == canary->y &&
          txn->mt_canary.z == canary->z)
        return MDBX_SUCCESS;
      txn->mt_canary.x = canary->x;
      txn->mt_canary.y = canary->y;
      txn->mt_canary.z = canary->z;
    }
    txn->mt_canary.v = txn->mt_txnid;
    txn->mt_flags |= MDBX_TXN_DIRTY;
  
    return MDBX_SUCCESS;
  }
  
  int mdbx_canary_get(const MDBX_txn *txn, MDBX_canary *canary) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(canary == NULL))
      return MDBX_EINVAL;
  
    *canary = txn->mt_canary;
    return MDBX_SUCCESS;
  }
  
  int mdbx_cursor_on_first(const MDBX_cursor *mc) {
    if (unlikely(mc == NULL))
      return MDBX_EINVAL;
  
    if (unlikely(mc->mc_signature != MDBX_MC_LIVE))
      return (mc->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                       : MDBX_EBADSIGN;
  
    if (!(mc->mc_flags & C_INITIALIZED))
      return mc->mc_db->md_entries ? MDBX_RESULT_FALSE : MDBX_RESULT_TRUE;
  
    for (unsigned i = 0; i < mc->mc_snum; ++i) {
      if (mc->mc_ki[i])
        return MDBX_RESULT_FALSE;
    }
  
    return MDBX_RESULT_TRUE;
  }
  
  int mdbx_cursor_on_last(const MDBX_cursor *mc) {
    if (unlikely(mc == NULL))
      return MDBX_EINVAL;
  
    if (unlikely(mc->mc_signature != MDBX_MC_LIVE))
      return (mc->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                       : MDBX_EBADSIGN;
  
    if (!(mc->mc_flags & C_INITIALIZED))
      return mc->mc_db->md_entries ? MDBX_RESULT_FALSE : MDBX_RESULT_TRUE;
  
    for (unsigned i = 0; i < mc->mc_snum; ++i) {
      unsigned nkeys = page_numkeys(mc->mc_pg[i]);
      if (mc->mc_ki[i] < nkeys - 1)
        return MDBX_RESULT_FALSE;
    }
  
    return MDBX_RESULT_TRUE;
  }
  
  int mdbx_cursor_eof(const MDBX_cursor *mc) {
    if (unlikely(mc == NULL))
      return MDBX_EINVAL;
  
    if (unlikely(mc->mc_signature != MDBX_MC_LIVE))
      return (mc->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                       : MDBX_EBADSIGN;
  
    if ((mc->mc_flags & C_INITIALIZED) == 0)
      return MDBX_RESULT_TRUE;
  
    if (mc->mc_snum == 0)
      return MDBX_RESULT_TRUE;
  
    if ((mc->mc_flags & C_EOF) &&
        mc->mc_ki[mc->mc_top] >= page_numkeys(mc->mc_pg[mc->mc_top]))
      return MDBX_RESULT_TRUE;
  
    return MDBX_RESULT_FALSE;
  }
  
  //------------------------------------------------------------------------------
  
  struct diff_result {
    ptrdiff_t diff;
    unsigned level;
    int root_nkeys;
  };
  
  /* calculates: r = x - y */
  __hot static int cursor_diff(const MDBX_cursor *const __restrict x,
                               const MDBX_cursor *const __restrict y,
                               struct diff_result *const __restrict r) {
    r->diff = 0;
    r->level = 0;
    r->root_nkeys = 0;
  
    if (unlikely(x->mc_signature != MDBX_MC_LIVE))
      return (x->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                      : MDBX_EBADSIGN;
  
    if (unlikely(y->mc_signature != MDBX_MC_LIVE))
      return (y->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                      : MDBX_EBADSIGN;
  
    int rc = check_txn(x->mc_txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(x->mc_txn != y->mc_txn))
      return MDBX_BAD_TXN;
  
    if (unlikely(y->mc_dbi != x->mc_dbi))
      return MDBX_EINVAL;
  
    if (unlikely(!(y->mc_flags & x->mc_flags & C_INITIALIZED)))
      return MDBX_ENODATA;
  
    while (likely(r->level < y->mc_snum && r->level < x->mc_snum)) {
      if (unlikely(y->mc_pg[r->level] != x->mc_pg[r->level]))
        return MDBX_PROBLEM;
  
      int nkeys = page_numkeys(y->mc_pg[r->level]);
      assert(nkeys > 0);
      if (r->level == 0)
        r->root_nkeys = nkeys;
  
      const int limit_ki = nkeys - 1;
      const int x_ki = x->mc_ki[r->level];
      const int y_ki = y->mc_ki[r->level];
      r->diff = ((x_ki < limit_ki) ? x_ki : limit_ki) -
                ((y_ki < limit_ki) ? y_ki : limit_ki);
      if (r->diff == 0) {
        r->level += 1;
        continue;
      }
  
      while (unlikely(r->diff == 1) &&
             likely(r->level + 1 < y->mc_snum && r->level + 1 < x->mc_snum)) {
        r->level += 1;
        /*   DB'PAGEs: 0------------------>MAX
         *
         *    CURSORs:       y < x
         *  STACK[i ]:         |
         *  STACK[+1]:  ...y++N|0++x...
         */
        nkeys = page_numkeys(y->mc_pg[r->level]);
        r->diff = (nkeys - y->mc_ki[r->level]) + x->mc_ki[r->level];
        assert(r->diff > 0);
      }
  
      while (unlikely(r->diff == -1) &&
             likely(r->level + 1 < y->mc_snum && r->level + 1 < x->mc_snum)) {
        r->level += 1;
        /*   DB'PAGEs: 0------------------>MAX
         *
         *    CURSORs:       x < y
         *  STACK[i ]:         |
         *  STACK[+1]:  ...x--N|0--y...
         */
        nkeys = page_numkeys(x->mc_pg[r->level]);
        r->diff = -(nkeys - x->mc_ki[r->level]) - y->mc_ki[r->level];
        assert(r->diff < 0);
      }
  
      return MDBX_SUCCESS;
    }
  
    r->diff = CMP2INT(x->mc_flags & C_EOF, y->mc_flags & C_EOF);
    return MDBX_SUCCESS;
  }
  
  __hot static ptrdiff_t estimate(const MDBX_db *db,
                                  struct diff_result *const __restrict dr) {
    /*        root: branch-page    => scale = leaf-factor * branch-factor^(N-1)
     *     level-1: branch-page(s) => scale = leaf-factor * branch-factor^2
     *     level-2: branch-page(s) => scale = leaf-factor * branch-factor
     *     level-N: branch-page(s) => scale = leaf-factor
     *  leaf-level: leaf-page(s)   => scale = 1
     */
    ptrdiff_t btree_power = (ptrdiff_t)db->md_depth - 2 - (ptrdiff_t)dr->level;
    if (btree_power < 0)
      return dr->diff;
  
    ptrdiff_t estimated =
        (ptrdiff_t)db->md_entries * dr->diff / (ptrdiff_t)db->md_leaf_pages;
    if (btree_power == 0)
      return estimated;
  
    if (db->md_depth < 4) {
      assert(dr->level == 0 && btree_power == 1);
      return (ptrdiff_t)db->md_entries * dr->diff / (ptrdiff_t)dr->root_nkeys;
    }
  
    /* average_branchpage_fillfactor = total(branch_entries) / branch_pages
       total(branch_entries) = leaf_pages + branch_pages - 1 (root page) */
    const size_t log2_fixedpoint = sizeof(size_t) - 1;
    const size_t half = UINT64_C(1) << (log2_fixedpoint - 1);
    const size_t factor =
        ((db->md_leaf_pages + db->md_branch_pages - 1) << log2_fixedpoint) /
        db->md_branch_pages;
    while (1) {
      switch ((size_t)btree_power) {
      default: {
        const size_t square = (factor * factor + half) >> log2_fixedpoint;
        const size_t quad = (square * square + half) >> log2_fixedpoint;
        do {
          estimated = estimated * quad + half;
          estimated >>= log2_fixedpoint;
          btree_power -= 4;
        } while (btree_power >= 4);
        continue;
      }
      case 3:
        estimated = estimated * factor + half;
        estimated >>= log2_fixedpoint;
        __fallthrough /* fall through */;
      case 2:
        estimated = estimated * factor + half;
        estimated >>= log2_fixedpoint;
        __fallthrough /* fall through */;
      case 1:
        estimated = estimated * factor + half;
        estimated >>= log2_fixedpoint;
        __fallthrough /* fall through */;
      case 0:
        if (unlikely(estimated > (ptrdiff_t)db->md_entries))
          return (ptrdiff_t)db->md_entries;
        if (unlikely(estimated < -(ptrdiff_t)db->md_entries))
          return -(ptrdiff_t)db->md_entries;
        return estimated;
      }
    }
  }
  
  int mdbx_estimate_distance(const MDBX_cursor *first, const MDBX_cursor *last,
                             ptrdiff_t *distance_items) {
    if (unlikely(first == NULL || last == NULL || distance_items == NULL))
      return MDBX_EINVAL;
  
    *distance_items = 0;
    struct diff_result dr;
    int rc = cursor_diff(last, first, &dr);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(dr.diff == 0) &&
        F_ISSET(first->mc_db->md_flags & last->mc_db->md_flags,
                MDBX_DUPSORT | C_INITIALIZED)) {
      first = &first->mc_xcursor->mx_cursor;
      last = &last->mc_xcursor->mx_cursor;
      rc = cursor_diff(first, last, &dr);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  
    if (likely(dr.diff != 0))
      *distance_items = estimate(first->mc_db, &dr);
  
    return MDBX_SUCCESS;
  }
  
  int mdbx_estimate_move(const MDBX_cursor *cursor, MDBX_val *key, MDBX_val *data,
                         MDBX_cursor_op move_op, ptrdiff_t *distance_items) {
    if (unlikely(cursor == NULL || distance_items == NULL ||
                 move_op == MDBX_GET_CURRENT || move_op == MDBX_GET_MULTIPLE))
      return MDBX_EINVAL;
  
    if (unlikely(cursor->mc_signature != MDBX_MC_LIVE))
      return (cursor->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
                                                           : MDBX_EBADSIGN;
  
    int rc = check_txn(cursor->mc_txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (!(cursor->mc_flags & C_INITIALIZED))
      return MDBX_ENODATA;
  
    MDBX_cursor_couple next;
    cursor_copy_internal(cursor, &next.outer);
    next.outer.mc_xcursor = NULL;
    if (cursor->mc_db->md_flags & MDBX_DUPSORT) {
      next.outer.mc_xcursor = &next.inner;
      rc = mdbx_xcursor_init0(&next.outer);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      MDBX_xcursor *mx = &container_of(cursor, MDBX_cursor_couple, outer)->inner;
      cursor_copy_internal(&mx->mx_cursor, &next.inner.mx_cursor);
    }
  
    MDBX_val stub = {0, 0};
    if (data == NULL) {
      const unsigned mask =
          1 << MDBX_GET_BOTH | 1 << MDBX_GET_BOTH_RANGE | 1 << MDBX_SET_KEY;
      if (unlikely(mask & (1 << move_op)))
        return MDBX_EINVAL;
      data = &stub;
    }
  
    if (key == NULL) {
      const unsigned mask = 1 << MDBX_GET_BOTH | 1 << MDBX_GET_BOTH_RANGE |
                            1 << MDBX_SET_KEY | 1 << MDBX_SET |
                            1 << MDBX_SET_RANGE;
      if (unlikely(mask & (1 << move_op)))
        return MDBX_EINVAL;
      key = &stub;
    }
  
    rc = mdbx_cursor_get(&next.outer, key, data, move_op);
    if (unlikely(rc != MDBX_SUCCESS &&
                 (rc != MDBX_NOTFOUND || !(next.outer.mc_flags & C_INITIALIZED))))
      return rc;
  
    return mdbx_estimate_distance(cursor, &next.outer, distance_items);
  }
  
  int mdbx_estimate_range(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *begin_key,
                          MDBX_val *begin_data, MDBX_val *end_key,
                          MDBX_val *end_data, ptrdiff_t *size_items) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!size_items))
      return MDBX_EINVAL;
  
    if (unlikely(begin_data && (begin_key == NULL || begin_key == MDBX_EPSILON)))
      return MDBX_EINVAL;
  
    if (unlikely(end_data && (end_key == NULL || end_key == MDBX_EPSILON)))
      return MDBX_EINVAL;
  
    if (unlikely(begin_key == MDBX_EPSILON && end_key == MDBX_EPSILON))
      return MDBX_EINVAL;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    MDBX_cursor_couple begin;
    /* LY: first, initialize cursor to refresh a DB in case it have DB_STALE */
    rc = mdbx_cursor_init(&begin.outer, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(begin.outer.mc_db->md_entries == 0)) {
      *size_items = 0;
      return MDBX_SUCCESS;
    }
  
    if (!begin_key) {
      if (unlikely(!end_key)) {
        /* LY: FIRST..LAST case */
        *size_items = (ptrdiff_t)begin.outer.mc_db->md_entries;
        return MDBX_SUCCESS;
      }
      MDBX_val stub = {0, 0};
      rc = mdbx_cursor_first(&begin.outer, &stub, &stub);
      if (unlikely(end_key == MDBX_EPSILON)) {
        /* LY: FIRST..+epsilon case */
        return (rc == MDBX_SUCCESS)
                   ? mdbx_cursor_count(&begin.outer, (size_t *)size_items)
                   : rc;
      }
    } else {
      if (unlikely(begin_key == MDBX_EPSILON)) {
        if (end_key == NULL) {
          /* LY: -epsilon..LAST case */
          MDBX_val stub = {0, 0};
          rc = mdbx_cursor_last(&begin.outer, &stub, &stub);
          return (rc == MDBX_SUCCESS)
                     ? mdbx_cursor_count(&begin.outer, (size_t *)size_items)
                     : rc;
        }
        /* LY: -epsilon..value case */
        assert(end_key != MDBX_EPSILON);
        begin_key = end_key;
      } else if (unlikely(end_key == MDBX_EPSILON)) {
        /* LY: value..+epsilon case */
        assert(begin_key != MDBX_EPSILON);
        end_key = begin_key;
      }
      if (end_key && !begin_data && !end_data &&
          (begin_key == end_key ||
           begin.outer.mc_dbx->md_cmp(begin_key, end_key) == 0)) {
        /* LY: single key case */
        int exact = 0;
        rc = mdbx_cursor_set(&begin.outer, begin_key, NULL, MDBX_SET, &exact);
        if (unlikely(rc != MDBX_SUCCESS)) {
          *size_items = 0;
          return (rc == MDBX_NOTFOUND) ? MDBX_SUCCESS : rc;
        }
        *size_items = 1;
        if (begin.outer.mc_xcursor != NULL) {
          MDBX_node *node = page_node(begin.outer.mc_pg[begin.outer.mc_top],
                                      begin.outer.mc_ki[begin.outer.mc_top]);
          if (F_ISSET(node_flags(node), F_DUPDATA)) {
            /* LY: return the number of duplicates for given key */
            mdbx_tassert(txn,
                         begin.outer.mc_xcursor == &begin.inner &&
                             (begin.inner.mx_cursor.mc_flags & C_INITIALIZED));
            *size_items =
                (sizeof(*size_items) >= sizeof(begin.inner.mx_db.md_entries) ||
                 begin.inner.mx_db.md_entries <= PTRDIFF_MAX)
                    ? (size_t)begin.inner.mx_db.md_entries
                    : PTRDIFF_MAX;
          }
        }
        return MDBX_SUCCESS;
      } else {
        rc = mdbx_cursor_set(&begin.outer, begin_key, begin_data,
                             begin_data ? MDBX_GET_BOTH_RANGE : MDBX_SET_RANGE,
                             NULL);
      }
    }
  
    if (unlikely(rc != MDBX_SUCCESS)) {
      if (rc != MDBX_NOTFOUND || !(begin.outer.mc_flags & C_INITIALIZED))
        return rc;
    }
  
    MDBX_cursor_couple end;
    rc = mdbx_cursor_init(&end.outer, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
    if (!end_key) {
      MDBX_val stub = {0, 0};
      rc = mdbx_cursor_last(&end.outer, &stub, &stub);
    } else {
      rc = mdbx_cursor_set(&end.outer, end_key, end_data,
                           end_data ? MDBX_GET_BOTH_RANGE : MDBX_SET_RANGE, NULL);
    }
    if (unlikely(rc != MDBX_SUCCESS)) {
      if (rc != MDBX_NOTFOUND || !(end.outer.mc_flags & C_INITIALIZED))
        return rc;
    }
  
    rc = mdbx_estimate_distance(&begin.outer, &end.outer, size_items);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
    assert(*size_items >= -(ptrdiff_t)begin.outer.mc_db->md_entries &&
           *size_items <= (ptrdiff_t)begin.outer.mc_db->md_entries);
  
  #if 0 /* LY: Was decided to returns as-is (i.e. negative) the estimation       \
         * results for an inverted ranges. */
  
    /* Commit 8ddfd1f34ad7cf7a3c4aa75d2e248ca7e639ed63
       Change-Id: If59eccf7311123ab6384c4b93f9b1fed5a0a10d1 */
  
    if (*size_items < 0) {
      /* LY: inverted range case */
      *size_items += (ptrdiff_t)begin.outer.mc_db->md_entries;
    } else if (*size_items == 0 && begin_key && end_key) {
      int cmp = begin.outer.mc_dbx->md_cmp(&origin_begin_key, &origin_end_key);
      if (cmp == 0 && (begin.inner.mx_cursor.mc_flags & C_INITIALIZED) &&
          begin_data && end_data)
        cmp = begin.outer.mc_dbx->md_dcmp(&origin_begin_data, &origin_end_data);
      if (cmp > 0) {
        /* LY: inverted range case with empty scope */
        *size_items = (ptrdiff_t)begin.outer.mc_db->md_entries;
      }
    }
    assert(*size_items >= 0 &&
           *size_items <= (ptrdiff_t)begin.outer.mc_db->md_entries);
  #endif
  
    return MDBX_SUCCESS;
  }
  
  //------------------------------------------------------------------------------
  
  /* Позволяет обновить или удалить существующую запись с получением
   * в old_data предыдущего значения данных. При этом если new_data равен
   * нулю, то выполняется удаление, иначе обновление/вставка.
   *
   * Текущее значение может находиться в уже измененной (грязной) странице.
   * В этом случае страница будет перезаписана при обновлении, а само старое
   * значение утрачено. Поэтому исходно в old_data должен быть передан
   * дополнительный буфер для копирования старого значения.
   * Если переданный буфер слишком мал, то функция вернет -1, установив
   * old_data->iov_len в соответствующее значение.
   *
   * Для не-уникальных ключей также возможен второй сценарий использования,
   * когда посредством old_data из записей с одинаковым ключом для
   * удаления/обновления выбирается конкретная. Для выбора этого сценария
   * во flags следует одновременно указать MDBX_CURRENT и MDBX_NOOVERWRITE.
   * Именно эта комбинация выбрана, так как она лишена смысла, и этим позволяет
   * идентифицировать запрос такого сценария.
   *
   * Функция может быть замещена соответствующими операциями с курсорами
   * после двух доработок (TODO):
   *  - внешняя аллокация курсоров, в том числе на стеке (без malloc).
   *  - получения статуса страницы по адресу (знать о P_DIRTY).
   */
  
  int mdbx_replace_ex(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
                      MDBX_val *new_data, MDBX_val *old_data,
                      MDBX_put_flags_t flags, MDBX_preserve_func preserver,
                      void *preserver_context) {
    int rc = check_txn_rw(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!key || !old_data || old_data == new_data))
      return MDBX_EINVAL;
  
    if (unlikely(old_data->iov_base == NULL && old_data->iov_len))
      return MDBX_EINVAL;
  
    if (unlikely(new_data == NULL &&
                 (flags & (MDBX_CURRENT | MDBX_RESERVE)) != MDBX_CURRENT))
      return MDBX_EINVAL;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    if (unlikely(flags &
                 ~(MDBX_NOOVERWRITE | MDBX_NODUPDATA | MDBX_ALLDUPS |
                   MDBX_RESERVE | MDBX_APPEND | MDBX_APPENDDUP | MDBX_CURRENT)))
      return MDBX_EINVAL;
  
    MDBX_cursor_couple cx;
    rc = mdbx_cursor_init(&cx.outer, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
    cx.outer.mc_next = txn->tw.cursors[dbi];
    txn->tw.cursors[dbi] = &cx.outer;
  
    MDBX_val present_key = *key;
    if (F_ISSET(flags, MDBX_CURRENT | MDBX_NOOVERWRITE)) {
      /* в old_data значение для выбора конкретного дубликата */
      if (unlikely(!(txn->mt_dbs[dbi].md_flags & MDBX_DUPSORT))) {
        rc = MDBX_EINVAL;
        goto bailout;
      }
  
      /* убираем лишний бит, он был признаком запрошенного режима */
      flags -= MDBX_NOOVERWRITE;
  
      rc = mdbx_cursor_get(&cx.outer, &present_key, old_data, MDBX_GET_BOTH);
      if (rc != MDBX_SUCCESS)
        goto bailout;
    } else {
      /* в old_data буфер для сохранения предыдущего значения */
      if (unlikely(new_data && old_data->iov_base == new_data->iov_base))
        return MDBX_EINVAL;
      MDBX_val present_data;
      rc = mdbx_cursor_get(&cx.outer, &present_key, &present_data, MDBX_SET_KEY);
      if (unlikely(rc != MDBX_SUCCESS)) {
        old_data->iov_base = NULL;
        old_data->iov_len = 0;
        if (rc != MDBX_NOTFOUND || (flags & MDBX_CURRENT))
          goto bailout;
      } else if (flags & MDBX_NOOVERWRITE) {
        rc = MDBX_KEYEXIST;
        *old_data = present_data;
        goto bailout;
      } else {
        MDBX_page *page = cx.outer.mc_pg[cx.outer.mc_top];
        if (txn->mt_dbs[dbi].md_flags & MDBX_DUPSORT) {
          if (flags & MDBX_CURRENT) {
            /* disallow update/delete for multi-values */
            MDBX_node *node = page_node(page, cx.outer.mc_ki[cx.outer.mc_top]);
            if (F_ISSET(node_flags(node), F_DUPDATA)) {
              mdbx_tassert(txn, XCURSOR_INITED(&cx.outer) &&
                                    cx.outer.mc_xcursor->mx_db.md_entries > 1);
              if (cx.outer.mc_xcursor->mx_db.md_entries > 1) {
                rc = MDBX_EMULTIVAL;
                goto bailout;
              }
            }
            /* В оригинальной LMDB флажок MDBX_CURRENT здесь приведет
             * к замене данных без учета MDBX_DUPSORT сортировки,
             * но здесь это в любом случае допустимо, так как мы
             * проверили что для ключа есть только одно значение. */
          }
        }
  
        if (IS_DIRTY(page)) {
          if (new_data && cmp_lenfast(&present_data, new_data) == 0) {
            /* если данные совпадают, то ничего делать не надо */
            *old_data = *new_data;
            goto bailout;
          }
          rc = preserver ? preserver(preserver_context, old_data,
                                     present_data.iov_base, present_data.iov_len)
                         : MDBX_SUCCESS;
          if (unlikely(rc != MDBX_SUCCESS))
            goto bailout;
        } else {
          *old_data = present_data;
        }
        flags |= MDBX_CURRENT;
      }
    }
  
    if (likely(new_data))
      rc = mdbx_cursor_put(&cx.outer, key, new_data, flags);
    else
      rc = mdbx_cursor_del(&cx.outer, flags & MDBX_ALLDUPS);
  
  bailout:
    txn->tw.cursors[dbi] = cx.outer.mc_next;
    return rc;
  }
  
  static int default_value_preserver(void *context, MDBX_val *target,
                                     const void *src, size_t bytes) {
    (void)context;
    if (unlikely(target->iov_len < bytes)) {
      target->iov_base = nullptr;
      target->iov_len = bytes;
      return MDBX_RESULT_TRUE;
    }
    memcpy(target->iov_base, src, target->iov_len = bytes);
    return MDBX_SUCCESS;
  }
  
  int mdbx_replace(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *key,
                   MDBX_val *new_data, MDBX_val *old_data,
                   MDBX_put_flags_t flags) {
    return mdbx_replace_ex(txn, dbi, key, new_data, old_data, flags,
                           default_value_preserver, nullptr);
  }
  
  /* Функция сообщает находится ли указанный адрес в "грязной" странице у
   * заданной пишущей транзакции. В конечном счете это позволяет избавиться от
   * лишнего копирования данных из НЕ-грязных страниц.
   *
   * "Грязные" страницы - это те, которые уже были изменены в ходе пишущей
   * транзакции. Соответственно, какие-либо дальнейшие изменения могут привести
   * к перезаписи таких страниц. Поэтому все функции, выполняющие изменения, в
   * качестве аргументов НЕ должны получать указатели на данные в таких
   * страницах. В свою очередь "НЕ грязные" страницы перед модификацией будут
   * скопированы.
   *
   * Другими словами, данные из "грязных" страниц должны быть либо скопированы
   * перед передачей в качестве аргументов для дальнейших модификаций, либо
   * отвергнуты на стадии проверки корректности аргументов.
   *
   * Таким образом, функция позволяет как избавиться от лишнего копирования,
   * так и выполнить более полную проверку аргументов.
   *
   * ВАЖНО: Передаваемый указатель должен указывать на начало данных. Только
   * так гарантируется что актуальный заголовок страницы будет физически
   * расположен в той-же странице памяти, в том числе для многостраничных
   * P_OVERFLOW страниц с длинными данными. */
  int mdbx_is_dirty(const MDBX_txn *txn, const void *ptr) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    const MDBX_env *env = txn->mt_env;
    const ptrdiff_t offset = (uint8_t *)ptr - env->me_map;
    if (offset >= 0) {
      const pgno_t pgno = bytes2pgno(env, offset);
      if (likely(pgno < txn->mt_next_pgno)) {
        if (txn->mt_flags & MDBX_TXN_RDONLY)
          return MDBX_RESULT_FALSE;
  
        const MDBX_page *page = pgno2page(env, pgno);
        if (unlikely(page->mp_pgno != pgno)) {
          /* The ptr pointed into middle of a large page,
           * not to the beginning of a data. */
          return MDBX_EINVAL;
        }
        if (unlikely(page->mp_flags & (P_DIRTY | P_LOOSE | P_KEEP | P_META)))
          return MDBX_RESULT_TRUE;
        if (likely(txn->tw.spill_pages == nullptr))
          return MDBX_RESULT_FALSE;
        return mdbx_pnl_exist(txn->tw.spill_pages, pgno << 1) ? MDBX_RESULT_TRUE
                                                              : MDBX_RESULT_FALSE;
      }
      if ((size_t)offset < env->me_dxb_mmap.limit) {
        /* Указатель адресует что-то в пределах mmap, но за границей
         * распределенных страниц. Такое может случится если mdbx_is_dirty()
         * вызывается после операции, в ходе которой грязная страница попала
         * в loose и затем была возвращена в нераспределенное пространство. */
        return MDBX_RESULT_TRUE;
      }
    }
  
    /* Страница вне используемого mmap-диапазона, т.е. либо в функцию был
     * передан некорректный адрес, либо адрес в теневой странице, которая была
     * выделена посредством malloc().
     *
     * Для режима WRITE_MAP режима страница однозначно "не грязная",
     * а для режимов без WRITE_MAP следует просматривать списки dirty
     * и spilled страниц у каких-либо транзакций (в том числе дочерних).
     *
     * Поэтому для WRITE_MAP возвращаем false, а для остальных режимов
     * всегда true. Такая логика имеет ряд преимуществ:
     *  - не тратим время на просмотр списков;
     *  - результат всегда безопасен (может быть ложно-положительным,
     *    но не ложно-отрицательным);
     *  - результат не зависит от вложенности транзакций и от относительного
     *    положения переданной транзакции в этой рекурсии. */
    return (env->me_flags & MDBX_WRITEMAP) ? MDBX_RESULT_FALSE : MDBX_RESULT_TRUE;
  }
  
  int mdbx_dbi_sequence(MDBX_txn *txn, MDBX_dbi dbi, uint64_t *result,
                        uint64_t increment) {
    int rc = check_txn(txn, MDBX_TXN_BLOCKED);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (unlikely(!mdbx_txn_dbi_exists(txn, dbi, DBI_USRVALID)))
      return MDBX_BAD_DBI;
  
    if (unlikely(TXN_DBI_CHANGED(txn, dbi)))
      return MDBX_BAD_DBI;
  
    if (unlikely(txn->mt_dbistate[dbi] & DBI_STALE)) {
      rc = mdbx_fetch_sdb(txn, dbi);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  
    MDBX_db *dbs = &txn->mt_dbs[dbi];
    if (likely(result))
      *result = dbs->md_seq;
  
    if (likely(increment > 0)) {
      if (unlikely(txn->mt_flags & MDBX_TXN_RDONLY))
        return MDBX_EACCESS;
  
      uint64_t new = dbs->md_seq + increment;
      if (unlikely(new < increment))
        return MDBX_RESULT_TRUE;
  
      mdbx_tassert(txn, new > dbs->md_seq);
      dbs->md_seq = new;
      txn->mt_flags |= MDBX_TXN_DIRTY;
      txn->mt_dbistate[dbi] |= DBI_DIRTY;
    }
  
    return MDBX_SUCCESS;
  }
  
  /*----------------------------------------------------------------------------*/
  
  __cold MDBX_NOTHROW_CONST_FUNCTION intptr_t mdbx_limits_pgsize_min(void) {
    return __inline_mdbx_limits_pgsize_min();
  }
  
  __cold MDBX_NOTHROW_CONST_FUNCTION intptr_t mdbx_limits_pgsize_max(void) {
    return __inline_mdbx_limits_pgsize_max();
  }
  
  __cold intptr_t mdbx_limits_dbsize_min(intptr_t pagesize) {
    if (pagesize < 1)
      pagesize = (intptr_t)mdbx_syspagesize();
    else if (unlikely(pagesize < (intptr_t)MIN_PAGESIZE ||
                      pagesize > (intptr_t)MAX_PAGESIZE ||
                      !is_powerof2((size_t)pagesize)))
      return -1;
  
    return MIN_PAGENO * pagesize;
  }
  
  __cold intptr_t mdbx_limits_dbsize_max(intptr_t pagesize) {
    if (pagesize < 1)
      pagesize = (intptr_t)mdbx_syspagesize();
    else if (unlikely(pagesize < (intptr_t)MIN_PAGESIZE ||
                      pagesize > (intptr_t)MAX_PAGESIZE ||
                      !is_powerof2((size_t)pagesize)))
      return -1;
  
    STATIC_ASSERT(MAX_MAPSIZE < INTPTR_MAX);
    const uint64_t limit = MAX_PAGENO * (uint64_t)pagesize;
    return (limit < (intptr_t)MAX_MAPSIZE) ? (intptr_t)limit
                                           : (intptr_t)MAX_MAPSIZE;
  }
  
  __cold intptr_t mdbx_limits_txnsize_max(intptr_t pagesize) {
    if (pagesize < 1)
      pagesize = (intptr_t)mdbx_syspagesize();
    else if (unlikely(pagesize < (intptr_t)MIN_PAGESIZE ||
                      pagesize > (intptr_t)MAX_PAGESIZE ||
                      !is_powerof2((size_t)pagesize)))
      return -1;
  
    STATIC_ASSERT(MAX_MAPSIZE < INTPTR_MAX);
    const uint64_t limit = pagesize * (uint64_t)(MDBX_DPL_TXNFULL - 1);
    return (limit < (intptr_t)MAX_MAPSIZE) ? (intptr_t)limit
                                           : (intptr_t)MAX_MAPSIZE;
  }
  
  /*** Key-making functions to avoid custom comparators *************************/
  
  static __always_inline double key2double(const int64_t key) {
    union {
      uint64_t u;
      double f;
    } casting;
  
    casting.u = (key < 0) ? key + UINT64_C(0x8000000000000000)
                          : UINT64_C(0xffffFFFFffffFFFF) - key;
    return casting.f;
  }
  
  static __always_inline uint64_t double2key(const double *const ptr) {
    STATIC_ASSERT(sizeof(double) == sizeof(int64_t));
    const int64_t i = *(const int64_t *)ptr;
    const uint64_t u = (i < 0) ? UINT64_C(0xffffFFFFffffFFFF) - i
                               : i + UINT64_C(0x8000000000000000);
    if (mdbx_assert_enabled()) {
      const double f = key2double(u);
      assert(memcmp(&f, ptr, 8) == 0);
    }
    return u;
  }
  
  static __always_inline float key2float(const int32_t key) {
    union {
      uint32_t u;
      float f;
    } casting;
  
    casting.u =
        (key < 0) ? key + UINT32_C(0x80000000) : UINT32_C(0xffffFFFF) - key;
    return casting.f;
  }
  
  static __always_inline uint32_t float2key(const float *const ptr) {
    STATIC_ASSERT(sizeof(float) == sizeof(int32_t));
    const int32_t i = *(const int32_t *)ptr;
    const uint32_t u =
        (i < 0) ? UINT32_C(0xffffFFFF) - i : i + UINT32_C(0x80000000);
    if (mdbx_assert_enabled()) {
      const float f = key2float(u);
      assert(memcmp(&f, ptr, 4) == 0);
    }
    return u;
  }
  
  uint64_t mdbx_key_from_double(const double ieee754_64bit) {
    return double2key(&ieee754_64bit);
  }
  
  uint64_t mdbx_key_from_ptrdouble(const double *const ieee754_64bit) {
    return double2key(ieee754_64bit);
  }
  
  uint32_t mdbx_key_from_float(const float ieee754_32bit) {
    return float2key(&ieee754_32bit);
  }
  
  uint32_t mdbx_key_from_ptrfloat(const float *const ieee754_32bit) {
    return float2key(ieee754_32bit);
  }
  
  MDBX_NOTHROW_CONST_FUNCTION uint64_t mdbx_key_from_int64(const int64_t i64) {
    return __inline_mdbx_key_from_int64(i64);
  }
  
  MDBX_NOTHROW_CONST_FUNCTION uint32_t mdbx_key_from_int32(const int32_t i32) {
    return __inline_mdbx_key_from_int32(i32);
  }
  
  #define IEEE754_DOUBLE_MANTISSA_SIZE 52
  #define IEEE754_DOUBLE_EXPONENTA_BIAS 0x3FF
  #define IEEE754_DOUBLE_EXPONENTA_MAX 0x7FF
  #define IEEE754_DOUBLE_IMPLICIT_LEAD UINT64_C(0x0010000000000000)
  #define IEEE754_DOUBLE_MANTISSA_MASK UINT64_C(0x000FFFFFFFFFFFFF)
  #define IEEE754_DOUBLE_MANTISSA_AMAX UINT64_C(0x001FFFFFFFFFFFFF)
  
  static __inline int clz64(uint64_t value) {
  #if __GNUC_PREREQ(4, 1) || __has_builtin(__builtin_clzl)
    if (sizeof(value) == sizeof(int))
      return __builtin_clz(value);
    if (sizeof(value) == sizeof(long))
      return __builtin_clzl(value);
  #if (defined(__SIZEOF_LONG_LONG__) && __SIZEOF_LONG_LONG__ == 8) ||            \
      __has_builtin(__builtin_clzll)
    return __builtin_clzll(value);
  #endif /* have(long long) && long long == uint64_t */
  #endif /* GNU C */
  
  #if defined(_MSC_VER)
    unsigned long index;
  #if defined(_M_AMD64) || defined(_M_ARM64) || defined(_M_X64)
    _BitScanReverse64(&index, value);
    return 63 - index;
  #else
    if (value > UINT32_MAX) {
      _BitScanReverse(&index, (uint32_t)(value >> 32));
      return 31 - index;
    }
    _BitScanReverse(&index, (uint32_t)value);
    return 63 - index;
  #endif
  #endif /* MSVC */
  
    value |= value >> 1;
    value |= value >> 2;
    value |= value >> 4;
    value |= value >> 8;
    value |= value >> 16;
    value |= value >> 32;
    static const uint8_t debruijn_clz64[64] = {
        63, 16, 62, 7,  15, 36, 61, 3,  6,  14, 22, 26, 35, 47, 60, 2,
        9,  5,  28, 11, 13, 21, 42, 19, 25, 31, 34, 40, 46, 52, 59, 1,
        17, 8,  37, 4,  23, 27, 48, 10, 29, 12, 43, 20, 32, 41, 53, 18,
        38, 24, 49, 30, 44, 33, 54, 39, 50, 45, 55, 51, 56, 57, 58, 0};
    return debruijn_clz64[value * UINT64_C(0x03F79D71B4CB0A89) >> 58];
  }
  
  static __inline uint64_t round_mantissa(const uint64_t u64, int shift) {
    assert(shift < 0 && u64 > 0);
    shift = -shift;
    const unsigned half = 1 << (shift - 1);
    const unsigned lsb = 1 & (unsigned)(u64 >> shift);
    const unsigned tie2even = 1 ^ lsb;
    return (u64 + half - tie2even) >> shift;
  }
  
  uint64_t mdbx_key_from_jsonInteger(const int64_t json_integer) {
    const uint64_t bias = UINT64_C(0x8000000000000000);
    if (json_integer > 0) {
      const uint64_t u64 = json_integer;
      int shift = clz64(u64) - (64 - IEEE754_DOUBLE_MANTISSA_SIZE - 1);
      uint64_t mantissa = u64 << shift;
      if (unlikely(shift < 0)) {
        mantissa = round_mantissa(u64, shift);
        if (mantissa > IEEE754_DOUBLE_MANTISSA_AMAX)
          mantissa = round_mantissa(u64, --shift);
      }
  
      assert(mantissa >= IEEE754_DOUBLE_IMPLICIT_LEAD &&
             mantissa <= IEEE754_DOUBLE_MANTISSA_AMAX);
      const uint64_t exponent =
          IEEE754_DOUBLE_EXPONENTA_BIAS + IEEE754_DOUBLE_MANTISSA_SIZE - shift;
      assert(exponent > 0 && exponent <= IEEE754_DOUBLE_EXPONENTA_MAX);
      const uint64_t key = bias + (exponent << IEEE754_DOUBLE_MANTISSA_SIZE) +
                           (mantissa - IEEE754_DOUBLE_IMPLICIT_LEAD);
  #if !defined(_MSC_VER) ||                                                      \
      defined(                                                                   \
          _DEBUG) /* Workaround for MSVC error LNK2019: unresolved external      \
                     symbol __except1 referenced in function __ftol3_except */
      assert(key == mdbx_key_from_double((double)json_integer));
  #endif /* Workaround for MSVC */
      return key;
    }
  
    if (json_integer < 0) {
      const uint64_t u64 = -json_integer;
      int shift = clz64(u64) - (64 - IEEE754_DOUBLE_MANTISSA_SIZE - 1);
      uint64_t mantissa = u64 << shift;
      if (unlikely(shift < 0)) {
        mantissa = round_mantissa(u64, shift);
        if (mantissa > IEEE754_DOUBLE_MANTISSA_AMAX)
          mantissa = round_mantissa(u64, --shift);
      }
  
      assert(mantissa >= IEEE754_DOUBLE_IMPLICIT_LEAD &&
             mantissa <= IEEE754_DOUBLE_MANTISSA_AMAX);
      const uint64_t exponent =
          IEEE754_DOUBLE_EXPONENTA_BIAS + IEEE754_DOUBLE_MANTISSA_SIZE - shift;
      assert(exponent > 0 && exponent <= IEEE754_DOUBLE_EXPONENTA_MAX);
      const uint64_t key = bias - 1 - (exponent << IEEE754_DOUBLE_MANTISSA_SIZE) -
                           (mantissa - IEEE754_DOUBLE_IMPLICIT_LEAD);
  #if !defined(_MSC_VER) ||                                                      \
      defined(                                                                   \
          _DEBUG) /* Workaround for MSVC error LNK2019: unresolved external      \
                     symbol __except1 referenced in function __ftol3_except */
      assert(key == mdbx_key_from_double((double)json_integer));
  #endif /* Workaround for MSVC */
      return key;
    }
  
    return bias;
  }
  
  int64_t mdbx_jsonInteger_from_key(const MDBX_val v) {
    assert(v.iov_len == 8);
    const uint64_t key = unaligned_peek_u64(2, v.iov_base);
    const uint64_t bias = UINT64_C(0x8000000000000000);
    const uint64_t covalent = (key > bias) ? key - bias : bias - key - 1;
    const int shift = IEEE754_DOUBLE_EXPONENTA_BIAS + 63 -
                      (IEEE754_DOUBLE_EXPONENTA_MAX &
                       (int)(covalent >> IEEE754_DOUBLE_MANTISSA_SIZE));
    if (unlikely(shift < 1))
      return (key < bias) ? INT64_MIN : INT64_MAX;
    if (unlikely(shift > 63))
      return 0;
  
    const uint64_t unscaled = ((covalent & IEEE754_DOUBLE_MANTISSA_MASK)
                               << (63 - IEEE754_DOUBLE_MANTISSA_SIZE)) +
                              bias;
    const int64_t absolute = unscaled >> shift;
    const int64_t value = (key < bias) ? -absolute : absolute;
    assert(key == mdbx_key_from_jsonInteger(value) ||
           (mdbx_key_from_jsonInteger(value - 1) < key &&
            key < mdbx_key_from_jsonInteger(value + 1)));
    return value;
  }
  
  double mdbx_double_from_key(const MDBX_val v) {
    assert(v.iov_len == 8);
    return key2double(unaligned_peek_u64(2, v.iov_base));
  }
  
  float mdbx_float_from_key(const MDBX_val v) {
    assert(v.iov_len == 4);
    return key2float(unaligned_peek_u32(2, v.iov_base));
  }
  
  int32_t mdbx_int32_from_key(const MDBX_val v) {
    assert(v.iov_len == 4);
    return (int32_t)(unaligned_peek_u32(2, v.iov_base) - UINT32_C(0x80000000));
  }
  
  int64_t mdbx_int64_from_key(const MDBX_val v) {
    assert(v.iov_len == 8);
    return (int64_t)(unaligned_peek_u64(2, v.iov_base) -
                     UINT64_C(0x8000000000000000));
  }
  
  __cold MDBX_cmp_func *mdbx_get_keycmp(unsigned flags) {
    return get_default_keycmp(flags);
  }
  
  __cold MDBX_cmp_func *mdbx_get_datacmp(unsigned flags) {
    return get_default_datacmp(flags);
  }
  
  /*** Attribute support functions for Nexenta **********************************/
  #ifdef MDBX_NEXENTA_ATTRS
  
  static __inline int mdbx_attr_peek(MDBX_val *data, mdbx_attr_t *attrptr) {
    if (unlikely(data->iov_len < sizeof(mdbx_attr_t)))
      return MDBX_INCOMPATIBLE;
  
    if (likely(attrptr != NULL))
      *attrptr = *(mdbx_attr_t *)data->iov_base;
    data->iov_len -= sizeof(mdbx_attr_t);
    data->iov_base =
        likely(data->iov_len > 0) ? ((mdbx_attr_t *)data->iov_base) + 1 : NULL;
  
    return MDBX_SUCCESS;
  }
  
  static __inline int mdbx_attr_poke(MDBX_val *reserved, MDBX_val *data,
                                     mdbx_attr_t attr, MDBX_put_flags_t flags) {
    mdbx_attr_t *space = reserved->iov_base;
    if (flags & MDBX_RESERVE) {
      if (likely(data != NULL)) {
        data->iov_base = data->iov_len ? space + 1 : NULL;
      }
    } else {
      *space = attr;
      if (likely(data != NULL)) {
        memcpy(space + 1, data->iov_base, data->iov_len);
      }
    }
  
    return MDBX_SUCCESS;
  }
  
  int mdbx_cursor_get_attr(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                           mdbx_attr_t *attrptr, MDBX_cursor_op op) {
    int rc = mdbx_cursor_get(mc, key, data, op);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    return mdbx_attr_peek(data, attrptr);
  }
  
  int mdbx_get_attr(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
                    uint64_t *attrptr) {
    int rc = mdbx_get(txn, dbi, key, data);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    return mdbx_attr_peek(data, attrptr);
  }
  
  int mdbx_put_attr(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
                    mdbx_attr_t attr, MDBX_put_flags_t flags) {
    MDBX_val reserve;
    reserve.iov_base = NULL;
    reserve.iov_len = (data ? data->iov_len : 0) + sizeof(mdbx_attr_t);
  
    int rc = mdbx_put(txn, dbi, key, &reserve, flags | MDBX_RESERVE);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    return mdbx_attr_poke(&reserve, data, attr, flags);
  }
  
  int mdbx_cursor_put_attr(MDBX_cursor *cursor, MDBX_val *key, MDBX_val *data,
                           mdbx_attr_t attr, MDBX_put_flags_t flags) {
    MDBX_val reserve;
    reserve.iov_base = NULL;
    reserve.iov_len = (data ? data->iov_len : 0) + sizeof(mdbx_attr_t);
  
    int rc = mdbx_cursor_put(cursor, key, &reserve, flags | MDBX_RESERVE);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    return mdbx_attr_poke(&reserve, data, attr, flags);
  }
  
  int mdbx_set_attr(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
                    mdbx_attr_t attr) {
    if (unlikely(!key || !txn))
      return MDBX_EINVAL;
  
    if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
      return MDBX_EBADSIGN;
  
    if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
      return MDBX_BAD_DBI;
  
    if (unlikely(txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_BLOCKED)))
      return (txn->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EACCESS : MDBX_BAD_TXN;
  
    MDBX_cursor_couple cx;
    MDBX_val old_data;
    int rc = mdbx_cursor_init(&cx.outer, txn, dbi);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
    rc = mdbx_cursor_set(&cx.outer, key, &old_data, MDBX_SET, NULL);
    if (unlikely(rc != MDBX_SUCCESS)) {
      if (rc == MDBX_NOTFOUND && data) {
        cx.outer.mc_next = txn->tw.cursors[dbi];
        txn->tw.cursors[dbi] = &cx.outer;
        rc = mdbx_cursor_put_attr(&cx.outer, key, data, attr, 0);
        txn->tw.cursors[dbi] = cx.outer.mc_next;
      }
      return rc;
    }
  
    mdbx_attr_t old_attr = 0;
    rc = mdbx_attr_peek(&old_data, &old_attr);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  
    if (old_attr == attr && (!data || (data->iov_len == old_data.iov_len &&
                                       memcmp(data->iov_base, old_data.iov_base,
                                              old_data.iov_len) == 0)))
      return MDBX_SUCCESS;
  
    cx.outer.mc_next = txn->tw.cursors[dbi];
    txn->tw.cursors[dbi] = &cx.outer;
    rc = mdbx_cursor_put_attr(&cx.outer, key, data ? data : &old_data, attr,
                              MDBX_CURRENT);
    txn->tw.cursors[dbi] = cx.outer.mc_next;
    return rc;
  }
  #endif /* MDBX_NEXENTA_ATTRS */
  
  /******************************************************************************/
  /* *INDENT-OFF* */
  /* clang-format off */
  
  __dll_export
  #ifdef __attribute_used__
      __attribute_used__
  #elif defined(__GNUC__) || __has_attribute(__used__)
      __attribute__((__used__))
  #endif
  #ifdef __attribute_externally_visible__
          __attribute_externally_visible__
  #elif (defined(__GNUC__) && !defined(__clang__)) ||                            \
      __has_attribute(__externally_visible__)
      __attribute__((__externally_visible__))
  #endif
      const struct MDBX_build_info mdbx_build = {
  #ifdef MDBX_BUILD_TIMESTAMP
      MDBX_BUILD_TIMESTAMP
  #else
      __DATE__ " " __TIME__
  #endif /* MDBX_BUILD_TIMESTAMP */
  
      ,
  #ifdef MDBX_BUILD_TARGET
      MDBX_BUILD_TARGET
  #else
    #if defined(__ANDROID_API__)
      "Android" STRINGIFY(__ANDROID_API__)
    #elif defined(__linux__) || defined(__gnu_linux__)
      "Linux"
    #elif defined(EMSCRIPTEN) || defined(__EMSCRIPTEN__)
      "webassembly"
    #elif defined(__CYGWIN__)
      "CYGWIN"
    #elif defined(_WIN64) || defined(_WIN32) || defined(__TOS_WIN__) \
        || defined(__WINDOWS__)
      "Windows"
    #elif defined(__APPLE__)
      #if (defined(TARGET_OS_IPHONE) && TARGET_OS_IPHONE) \
        || (defined(TARGET_IPHONE_SIMULATOR) && TARGET_IPHONE_SIMULATOR)
        "iOS"
      #else
        "MacOS"
      #endif
    #elif defined(__FreeBSD__)
      "FreeBSD"
    #elif defined(__DragonFly__)
      "DragonFlyBSD"
    #elif defined(__NetBSD__)
      "NetBSD"
    #elif defined(__OpenBSD__)
      "OpenBSD"
    #elif defined(__bsdi__)
      "UnixBSDI"
    #elif defined(__MACH__)
      "MACH"
    #elif (defined(_HPUX_SOURCE) || defined(__hpux) || defined(__HP_aCC))
      "HPUX"
    #elif defined(_AIX)
      "AIX"
    #elif defined(__sun) && defined(__SVR4)
      "Solaris"
    #elif defined(__BSD__) || defined(BSD)
      "UnixBSD"
    #elif defined(__unix__) || defined(UNIX) || defined(__unix) \
        || defined(__UNIX) || defined(__UNIX__)
      "UNIX"
    #elif defined(_POSIX_VERSION)
      "POSIX" STRINGIFY(_POSIX_VERSION)
    #else
      "UnknownOS"
    #endif /* Target OS */
  
      "-"
  
    #if defined(__amd64__)
      "AMD64"
    #elif defined(__ia32__)
      "IA32"
    #elif defined(__e2k__) || defined(__elbrus__)
      "Elbrus"
    #elif defined(__alpha__) || defined(__alpha) || defined(_M_ALPHA)
      "Alpha"
    #elif defined(__aarch64__) || defined(_M_ARM64)
      "ARM64"
    #elif defined(__arm__) || defined(__thumb__) || defined(__TARGET_ARCH_ARM) \
        || defined(__TARGET_ARCH_THUMB) || defined(_ARM) || defined(_M_ARM) \
        || defined(_M_ARMT) || defined(__arm)
      "ARM"
    #elif defined(__mips64) || defined(__mips64__) || (defined(__mips) && (__mips >= 64))
      "MIPS64"
    #elif if defined(__mips__) || defined(__mips) || defined(_R4000) || defined(__MIPS__)
      "MIPS"
    #elif defined(__hppa64__) || defined(__HPPA64__) || defined(__hppa64)
      "PARISC64"
    #elif defined(__hppa__) || defined(__HPPA__) || defined(__hppa)
      "PARISC"
    #elif defined(__ia64__) || defined(__ia64) || defined(_IA64) \
        || defined(__IA64__) || defined(_M_IA64) || defined(__itanium__)
      "Itanium"
    #elif defined(__powerpc64__) || defined(__ppc64__) || defined(__ppc64) \
        || defined(__powerpc64) || defined(_ARCH_PPC64)
      "PowerPC64"
    #elif defined(__powerpc__) || defined(__ppc__) || defined(__powerpc) \
        || defined(__ppc) || defined(_ARCH_PPC) || defined(__PPC__) || defined(__POWERPC__)
      "PowerPC"
    #elif defined(__sparc64__) || defined(__sparc64)
      "SPARC64"
    #elif defined(__sparc__) || defined(__sparc)
      "SPARC"
    #elif defined(__s390__) || defined(__s390) || defined(__zarch__) || defined(__zarch)
      "S390"
    #else
      "UnknownARCH"
    #endif
  #endif /* MDBX_BUILD_TARGET */
  
  #ifdef MDBX_BUILD_TYPE
  # if defined(_MSC_VER)
  #   pragma message("Configuration-depended MDBX_BUILD_TYPE: " MDBX_BUILD_TYPE)
  # endif
      "-" MDBX_BUILD_TYPE
  #endif /* MDBX_BUILD_TYPE */
      ,
      "MDBX_DEBUG=" STRINGIFY(MDBX_DEBUG)
      " MDBX_WORDBITS=" STRINGIFY(MDBX_WORDBITS)
      " BYTE_ORDER="
  #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
      "LITTLE_ENDIAN"
  #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
      "BIG_ENDIAN"
  #else
      #error "FIXME: Unsupported byte order"
  #endif /* __BYTE_ORDER__ */
  #if MDBX_HUGE_TRANSACTIONS
      " MDBX_HUGE_TRANSACTIONS=YES"
  #endif /* MDBX_HUGE_TRANSACTIONS */
      " MDBX_ENV_CHECKPID=" MDBX_ENV_CHECKPID_CONFIG
      " MDBX_TXN_CHECKOWNER=" MDBX_TXN_CHECKOWNER_CONFIG
      " MDBX_64BIT_ATOMIC=" MDBX_64BIT_ATOMIC_CONFIG
      " MDBX_64BIT_CAS=" MDBX_64BIT_CAS_CONFIG
      " MDBX_TRUST_RTC=" MDBX_TRUST_RTC_CONFIG
  #ifdef __SANITIZE_ADDRESS__
      " SANITIZE_ADDRESS=YES"
  #endif /* __SANITIZE_ADDRESS__ */
  #ifdef MDBX_USE_VALGRIND
      " MDBX_USE_VALGRIND=YES"
  #endif /* MDBX_USE_VALGRIND */
  #ifdef MDBX_FORCE_ASSERTIONS
      " MDBX_FORCE_ASSERTIONS=YES"
  #endif /* MDBX_FORCE_ASSERTIONS */
  #ifdef _GNU_SOURCE
      " _GNU_SOURCE=YES"
  #else
      " _GNU_SOURCE=NO"
  #endif /* _GNU_SOURCE */
  #ifdef __APPLE__
      " MDBX_OSX_SPEED_INSTEADOF_DURABILITY=" STRINGIFY(MDBX_OSX_SPEED_INSTEADOF_DURABILITY)
  #endif /* MacOS */
  #if defined(_WIN32) || defined(_WIN64)
      " MDBX_AVOID_CRT=" STRINGIFY(MDBX_AVOID_CRT)
      " MDBX_CONFIG_MANUAL_TLS_CALLBACK=" STRINGIFY(MDBX_CONFIG_MANUAL_TLS_CALLBACK)
      " MDBX_BUILD_SHARED_LIBRARY=" STRINGIFY(MDBX_BUILD_SHARED_LIBRARY)
      " WINVER=" STRINGIFY(WINVER)
  #else /* Windows */
      " MDBX_LOCKING=" MDBX_LOCKING_CONFIG
      " MDBX_USE_OFDLOCKS=" MDBX_USE_OFDLOCKS_CONFIG
  #endif /* !Windows */
      " MDBX_CACHELINE_SIZE=" STRINGIFY(MDBX_CACHELINE_SIZE)
      " MDBX_CPU_WRITEBACK_INCOHERENT=" STRINGIFY(MDBX_CPU_WRITEBACK_INCOHERENT)
      " MDBX_MMAP_INCOHERENT_CPU_CACHE=" STRINGIFY(MDBX_MMAP_INCOHERENT_CPU_CACHE)
      " MDBX_MMAP_INCOHERENT_FILE_WRITE=" STRINGIFY(MDBX_MMAP_INCOHERENT_FILE_WRITE)
      " MDBX_UNALIGNED_OK=" STRINGIFY(MDBX_UNALIGNED_OK)
      " MDBX_PNL_ASCENDING=" STRINGIFY(MDBX_PNL_ASCENDING)
      ,
  #ifdef MDBX_BUILD_COMPILER
      MDBX_BUILD_COMPILER
  #else
    #ifdef __INTEL_COMPILER
      "Intel C/C++ " STRINGIFY(__INTEL_COMPILER)
    #elsif defined(__apple_build_version__)
      "Apple clang " STRINGIFY(__apple_build_version__)
    #elif defined(__ibmxl__)
      "IBM clang C " STRINGIFY(__ibmxl_version__) "." STRINGIFY(__ibmxl_release__)
      "." STRINGIFY(__ibmxl_modification__) "." STRINGIFY(__ibmxl_ptf_fix_level__)
    #elif defined(__clang__)
      "clang " STRINGIFY(__clang_version__)
    #elif defined(__MINGW64__)
      "MINGW-64 " STRINGIFY(__MINGW64_MAJOR_VERSION) "." STRINGIFY(__MINGW64_MINOR_VERSION)
    #elif defined(__MINGW32__)
      "MINGW-32 " STRINGIFY(__MINGW32_MAJOR_VERSION) "." STRINGIFY(__MINGW32_MINOR_VERSION)
    #elif defined(__IBMC__)
      "IBM C " STRINGIFY(__IBMC__)
    #elif defined(__GNUC__)
      "GNU C/C++ "
      #ifdef __VERSION__
        __VERSION__
      #else
        STRINGIFY(__GNUC__) "." STRINGIFY(__GNUC_MINOR__) "." STRINGIFY(__GNUC_PATCHLEVEL__)
      #endif
    #elif defined(_MSC_VER)
      "MSVC " STRINGIFY(_MSC_FULL_VER) "-" STRINGIFY(_MSC_BUILD)
    #else
      "Unknown compiler"
    #endif
  #endif /* MDBX_BUILD_COMPILER */
      ,
  #ifdef MDBX_BUILD_FLAGS_CONFIG
      MDBX_BUILD_FLAGS_CONFIG
  #endif /* MDBX_BUILD_FLAGS_CONFIG */
  #ifdef MDBX_BUILD_FLAGS
      MDBX_BUILD_FLAGS
  #endif /* MDBX_BUILD_FLAGS */
  #if !(defined(MDBX_BUILD_FLAGS_CONFIG) || defined(MDBX_BUILD_FLAGS))
      "undefined (please use correct build script)"
  #ifdef _MSC_VER
  #pragma message("warning: Build flags undefined. Please use correct build script")
  #else
  #warning "Build flags undefined. Please use correct build script"
  #endif // _MSC_VER
  #endif
  };
  
  #ifdef __SANITIZE_ADDRESS__
  LIBMDBX_API __attribute__((__weak__)) const char *__asan_default_options() {
    return "symbolize=1:allow_addr2line=1:"
  #ifdef _DEBUG
           "debug=1:"
  #endif /* _DEBUG */
           "report_globals=1:"
           "replace_str=1:replace_intrin=1:"
           "malloc_context_size=9:"
           "detect_leaks=1:"
           "check_printf=1:"
           "detect_deadlocks=1:"
  #ifndef LTO_ENABLED
           "check_initialization_order=1:"
  #endif
           "detect_stack_use_after_return=1:"
           "intercept_tls_get_addr=1:"
           "decorate_proc_maps=1:"
           "abort_on_error=1";
  }
  #endif /* __SANITIZE_ADDRESS__ */
  
  /* *INDENT-ON* */
  /* clang-format on */
  /* https://en.wikipedia.org/wiki/Operating_system_abstraction_layer */
  
  /*
   * Copyright 2015-2020 Leonid Yuriev <leo@yuriev.ru>
   * and other libmdbx authors: please see AUTHORS file.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted only as authorized by the OpenLDAP
   * Public License.
   *
   * A copy of this license is available in the file LICENSE in the
   * top-level directory of the distribution or, alternatively, at
   * <http://www.OpenLDAP.org/license.html>.
   */
  
  
  #if defined(_WIN32) || defined(_WIN64)
  
  #include <winioctl.h>
  
  static int waitstatus2errcode(DWORD result) {
    switch (result) {
    case WAIT_OBJECT_0:
      return MDBX_SUCCESS;
    case WAIT_FAILED:
      return GetLastError();
    case WAIT_ABANDONED:
      return ERROR_ABANDONED_WAIT_0;
    case WAIT_IO_COMPLETION:
      return ERROR_USER_APC;
    case WAIT_TIMEOUT:
      return ERROR_TIMEOUT;
    default:
      return ERROR_UNHANDLED_ERROR;
    }
  }
  
  /* Map a result from an NTAPI call to WIN32 error code. */
  static int ntstatus2errcode(NTSTATUS status) {
    DWORD dummy;
    OVERLAPPED ov;
    memset(&ov, 0, sizeof(ov));
    ov.Internal = status;
    return GetOverlappedResult(NULL, &ov, &dummy, FALSE) ? MDBX_SUCCESS
                                                         : GetLastError();
  }
  
  /* We use native NT APIs to setup the memory map, so that we can
   * let the DB file grow incrementally instead of always preallocating
   * the full size. These APIs are defined in <wdm.h> and <ntifs.h>
   * but those headers are meant for driver-level development and
   * conflict with the regular user-level headers, so we explicitly
   * declare them here. Using these APIs also means we must link to
   * ntdll.dll, which is not linked by default in user code. */
  
  extern NTSTATUS NTAPI NtCreateSection(
      OUT PHANDLE SectionHandle, IN ACCESS_MASK DesiredAccess,
      IN OPTIONAL POBJECT_ATTRIBUTES ObjectAttributes,
      IN OPTIONAL PLARGE_INTEGER MaximumSize, IN ULONG SectionPageProtection,
      IN ULONG AllocationAttributes, IN OPTIONAL HANDLE FileHandle);
  
  typedef struct _SECTION_BASIC_INFORMATION {
    ULONG Unknown;
    ULONG SectionAttributes;
    LARGE_INTEGER SectionSize;
  } SECTION_BASIC_INFORMATION, *PSECTION_BASIC_INFORMATION;
  
  extern NTSTATUS NTAPI NtMapViewOfSection(
      IN HANDLE SectionHandle, IN HANDLE ProcessHandle, IN OUT PVOID *BaseAddress,
      IN ULONG_PTR ZeroBits, IN SIZE_T CommitSize,
      IN OUT OPTIONAL PLARGE_INTEGER SectionOffset, IN OUT PSIZE_T ViewSize,
      IN SECTION_INHERIT InheritDisposition, IN ULONG AllocationType,
      IN ULONG Win32Protect);
  
  extern NTSTATUS NTAPI NtUnmapViewOfSection(IN HANDLE ProcessHandle,
                                             IN OPTIONAL PVOID BaseAddress);
  
  extern NTSTATUS NTAPI NtClose(HANDLE Handle);
  
  extern NTSTATUS NTAPI NtAllocateVirtualMemory(
      IN HANDLE ProcessHandle, IN OUT PVOID *BaseAddress, IN ULONG_PTR ZeroBits,
      IN OUT PSIZE_T RegionSize, IN ULONG AllocationType, IN ULONG Protect);
  
  extern NTSTATUS NTAPI NtFreeVirtualMemory(IN HANDLE ProcessHandle,
                                            IN PVOID *BaseAddress,
                                            IN OUT PSIZE_T RegionSize,
                                            IN ULONG FreeType);
  
  #ifndef WOF_CURRENT_VERSION
  typedef struct _WOF_EXTERNAL_INFO {
    DWORD Version;
    DWORD Provider;
  } WOF_EXTERNAL_INFO, *PWOF_EXTERNAL_INFO;
  #endif /* WOF_CURRENT_VERSION */
  
  #ifndef WIM_PROVIDER_CURRENT_VERSION
  #define WIM_PROVIDER_HASH_SIZE 20
  
  typedef struct _WIM_PROVIDER_EXTERNAL_INFO {
    DWORD Version;
    DWORD Flags;
    LARGE_INTEGER DataSourceId;
    BYTE ResourceHash[WIM_PROVIDER_HASH_SIZE];
  } WIM_PROVIDER_EXTERNAL_INFO, *PWIM_PROVIDER_EXTERNAL_INFO;
  #endif /* WIM_PROVIDER_CURRENT_VERSION */
  
  #ifndef FILE_PROVIDER_CURRENT_VERSION
  typedef struct _FILE_PROVIDER_EXTERNAL_INFO_V1 {
    ULONG Version;
    ULONG Algorithm;
    ULONG Flags;
  } FILE_PROVIDER_EXTERNAL_INFO_V1, *PFILE_PROVIDER_EXTERNAL_INFO_V1;
  #endif /* FILE_PROVIDER_CURRENT_VERSION */
  
  #ifndef STATUS_OBJECT_NOT_EXTERNALLY_BACKED
  #define STATUS_OBJECT_NOT_EXTERNALLY_BACKED ((NTSTATUS)0xC000046DL)
  #endif
  #ifndef STATUS_INVALID_DEVICE_REQUEST
  #define STATUS_INVALID_DEVICE_REQUEST ((NTSTATUS)0xC0000010L)
  #endif
  #ifndef STATUS_NOT_SUPPORTED
  #define STATUS_NOT_SUPPORTED ((NTSTATUS)0xC00000BBL)
  #endif
  
  #ifndef FILE_DEVICE_FILE_SYSTEM
  #define FILE_DEVICE_FILE_SYSTEM 0x00000009
  #endif
  
  #ifndef FSCTL_GET_EXTERNAL_BACKING
  #define FSCTL_GET_EXTERNAL_BACKING                                             \
    CTL_CODE(FILE_DEVICE_FILE_SYSTEM, 196, METHOD_BUFFERED, FILE_ANY_ACCESS)
  #endif
  
  #endif /* _WIN32 || _WIN64 */
  
  /*----------------------------------------------------------------------------*/
  
  #if defined(__UCLIBC__)
  __extern_C void __assert(const char *, const char *, unsigned int, const char *)
  #ifdef __THROW
      __THROW
  #else
      __nothrow
  #endif /* __THROW */
      MDBX_NORETURN;
  #define __assert_fail(assertion, file, line, function)                         \
    __assert(assertion, file, line, function)
  
  #elif _POSIX_C_SOURCE > 200212 &&                                              \
      /* workaround for avoid musl libc wrong prototype */ (                     \
          defined(__GLIBC__) || defined(__GNU_LIBRARY__))
  /* Prototype should match libc runtime. ISO POSIX (2003) & LSB 1.x-3.x */
  __extern_C void __assert_fail(const char *assertion, const char *file,
                                unsigned line, const char *function)
  #ifdef __THROW
      __THROW
  #else
      __nothrow
  #endif /* __THROW */
      MDBX_NORETURN;
  
  #elif defined(__APPLE__) || defined(__MACH__)
  __extern_C void __assert_rtn(const char *function, const char *file, int line,
                               const char *assertion) /* __nothrow */
  #ifdef __dead2
      __dead2
  #else
      MDBX_NORETURN
  #endif /* __dead2 */
  #ifdef __disable_tail_calls
      __disable_tail_calls
  #endif /* __disable_tail_calls */
      ;
  
  #define __assert_fail(assertion, file, line, function)                         \
    __assert_rtn(function, file, line, assertion)
  #elif defined(__sun) || defined(__SVR4) || defined(__svr4__)
  __extern_C void __assert_c99(const char *assection, const char *file, int line,
                               const char *function) MDBX_NORETURN;
  #define __assert_fail(assertion, file, line, function)                         \
    __assert_c99(assertion, file, line, function)
  #elif defined(__OpenBSD__)
  __extern_C __dead void __assert2(const char *file, int line,
                                   const char *function,
                                   const char *assertion) /* __nothrow */;
  #define __assert_fail(assertion, file, line, function)                         \
    __assert2(file, line, function, assertion)
  #elif defined(__NetBSD__)
  __extern_C __dead void __assert13(const char *file, int line,
                                    const char *function,
                                    const char *assertion) /* __nothrow */;
  #define __assert_fail(assertion, file, line, function)                         \
    __assert13(file, line, function, assertion)
  #elif defined(__FreeBSD__) || defined(__BSD__) || defined(__bsdi__) ||         \
      defined(__DragonFly__)
  __extern_C void __assert(const char *function, const char *file, int line,
                           const char *assertion) /* __nothrow */
  #ifdef __dead2
      __dead2
  #else
      MDBX_NORETURN
  #endif /* __dead2 */
  #ifdef __disable_tail_calls
      __disable_tail_calls
  #endif /* __disable_tail_calls */
      ;
  #define __assert_fail(assertion, file, line, function)                         \
    __assert(function, file, line, assertion)
  
  #endif /* __assert_fail */
  
  #if !defined(__ANDROID_API__) || MDBX_DEBUG
  
  void __cold mdbx_assert_fail(const MDBX_env *env, const char *msg,
                               const char *func, int line) {
  #if MDBX_DEBUG
    if (env && env->me_assert_func) {
      env->me_assert_func(env, msg, func, line);
      return;
    }
  #else
    (void)env;
  #endif /* MDBX_DEBUG */
  
    if (mdbx_debug_logger)
      mdbx_debug_log(MDBX_LOG_FATAL, func, line, "assert: %s\n", msg);
    else {
  #if defined(_WIN32) || defined(_WIN64)
      char *message = nullptr;
      const int num = mdbx_asprintf(&message, "\r\nMDBX-ASSERTION: %s, %s:%u",
                                    msg, func ? func : "unknown", line);
      if (num < 1 || !message)
        message = "<troubles with assertion-message preparation>";
      OutputDebugStringA(message);
      if (IsDebuggerPresent())
        DebugBreak();
  #elif defined(__ANDROID_API__)
      __android_log_assert(msg, "mdbx", "%s:%u", func, line);
  #else
      __assert_fail(msg, "mdbx", line, func);
  #endif
    }
  
  #if defined(_WIN32) || defined(_WIN64)
    FatalExit(ERROR_UNHANDLED_ERROR);
  #else
    abort();
  #endif
  }
  
  #endif /* __ANDROID_API__ || MDBX_DEBUG */
  
  __cold void mdbx_panic(const char *fmt, ...) {
    va_list ap;
    va_start(ap, fmt);
  
    char *message = nullptr;
    const int num = mdbx_vasprintf(&message, fmt, ap);
    va_end(ap);
    const char *const const_message =
        (num < 1 || !message) ? "<troubles with panic-message preparation>"
                              : message;
  
  #if defined(_WIN32) || defined(_WIN64)
    OutputDebugStringA("\r\nMDBX-PANIC: ");
    OutputDebugStringA(const_message);
    if (IsDebuggerPresent())
      DebugBreak();
    FatalExit(ERROR_UNHANDLED_ERROR);
  #else
  #if defined(__ANDROID_API__)
    __android_log_assert("panic", "mdbx", "%s", const_message);
  #else
    __assert_fail(const_message, "mdbx", 0, "panic");
  #endif /* __ANDROID_API__ */
    abort();
  #endif
  }
  
  /*----------------------------------------------------------------------------*/
  
  #ifndef mdbx_vasprintf
  MDBX_INTERNAL_FUNC int mdbx_vasprintf(char **strp, const char *fmt,
                                        va_list ap) {
    va_list ones;
    va_copy(ones, ap);
    int needed = vsnprintf(nullptr, 0, fmt, ap);
  
    if (unlikely(needed < 0 || needed >= INT_MAX)) {
      *strp = nullptr;
      va_end(ones);
      return needed;
    }
  
    *strp = mdbx_malloc(needed + 1);
    if (unlikely(*strp == nullptr)) {
      va_end(ones);
  #if defined(_WIN32) || defined(_WIN64)
      SetLastError(MDBX_ENOMEM);
  #else
      errno = MDBX_ENOMEM;
  #endif
      return -1;
    }
  
    int actual = vsnprintf(*strp, needed + 1, fmt, ones);
    va_end(ones);
  
    assert(actual == needed);
    if (unlikely(actual < 0)) {
      mdbx_free(*strp);
      *strp = nullptr;
    }
    return actual;
  }
  #endif /* mdbx_vasprintf */
  
  #ifndef mdbx_asprintf
  MDBX_INTERNAL_FUNC int mdbx_asprintf(char **strp, const char *fmt, ...) {
    va_list ap;
    va_start(ap, fmt);
    int rc = mdbx_vasprintf(strp, fmt, ap);
    va_end(ap);
    return rc;
  }
  #endif /* mdbx_asprintf */
  
  #ifndef mdbx_memalign_alloc
  MDBX_INTERNAL_FUNC int mdbx_memalign_alloc(size_t alignment, size_t bytes,
                                             void **result) {
    assert(is_powerof2(alignment) && alignment >= sizeof(void *));
  #if defined(_WIN32) || defined(_WIN64)
    (void)alignment;
    *result = VirtualAlloc(NULL, bytes, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
    return *result ? MDBX_SUCCESS : MDBX_ENOMEM /* ERROR_OUTOFMEMORY */;
  #elif defined(_ISOC11_SOURCE)
    *result = aligned_alloc(alignment, ceil_powerof2(bytes, alignment));
    return *result ? MDBX_SUCCESS : errno;
  #elif _POSIX_VERSION >= 200112L &&                                             \
      (!defined(__ANDROID_API__) || __ANDROID_API__ >= 17)
    *result = nullptr;
    return posix_memalign(result, alignment, bytes);
  #elif __GLIBC_PREREQ(2, 16) || __STDC_VERSION__ >= 201112L
    *result = memalign(alignment, bytes);
    return *result ? MDBX_SUCCESS : errno;
  #else
  #error FIXME
  #endif
  }
  #endif /* mdbx_memalign_alloc */
  
  #ifndef mdbx_memalign_free
  MDBX_INTERNAL_FUNC void mdbx_memalign_free(void *ptr) {
  #if defined(_WIN32) || defined(_WIN64)
    VirtualFree(ptr, 0, MEM_RELEASE);
  #else
    mdbx_free(ptr);
  #endif
  }
  #endif /* mdbx_memalign_free */
  
  #ifndef mdbx_strdup
  char *mdbx_strdup(const char *str) {
    if (!str)
      return NULL;
    size_t bytes = strlen(str) + 1;
    char *dup = mdbx_malloc(bytes);
    if (dup)
      memcpy(dup, str, bytes);
    return dup;
  }
  #endif /* mdbx_strdup */
  
  /*----------------------------------------------------------------------------*/
  
  MDBX_INTERNAL_FUNC int mdbx_condpair_init(mdbx_condpair_t *condpair) {
    int rc;
    memset(condpair, 0, sizeof(mdbx_condpair_t));
  #if defined(_WIN32) || defined(_WIN64)
    if ((condpair->mutex = CreateMutexW(NULL, FALSE, NULL)) == NULL) {
      rc = GetLastError();
      goto bailout_mutex;
    }
    if ((condpair->event[0] = CreateEventW(NULL, FALSE, FALSE, NULL)) == NULL) {
      rc = GetLastError();
      goto bailout_event;
    }
    if ((condpair->event[1] = CreateEventW(NULL, FALSE, FALSE, NULL)) != NULL)
      return MDBX_SUCCESS;
  
    rc = GetLastError();
    (void)CloseHandle(condpair->event[0]);
  bailout_event:
    (void)CloseHandle(condpair->mutex);
  #else
    rc = pthread_mutex_init(&condpair->mutex, NULL);
    if (unlikely(rc != 0))
      goto bailout_mutex;
    rc = pthread_cond_init(&condpair->cond[0], NULL);
    if (unlikely(rc != 0))
      goto bailout_cond;
    rc = pthread_cond_init(&condpair->cond[1], NULL);
    if (likely(rc == 0))
      return MDBX_SUCCESS;
  
    (void)pthread_cond_destroy(&condpair->cond[0]);
  bailout_cond:
    (void)pthread_mutex_destroy(&condpair->mutex);
  #endif
  bailout_mutex:
    memset(condpair, 0, sizeof(mdbx_condpair_t));
    return rc;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_condpair_destroy(mdbx_condpair_t *condpair) {
  #if defined(_WIN32) || defined(_WIN64)
    int rc = CloseHandle(condpair->mutex) ? MDBX_SUCCESS : GetLastError();
    rc = CloseHandle(condpair->event[0]) ? rc : GetLastError();
    rc = CloseHandle(condpair->event[1]) ? rc : GetLastError();
  #else
    int err, rc = pthread_mutex_destroy(&condpair->mutex);
    rc = (err = pthread_cond_destroy(&condpair->cond[0])) ? err : rc;
    rc = (err = pthread_cond_destroy(&condpair->cond[1])) ? err : rc;
  #endif
    memset(condpair, 0, sizeof(mdbx_condpair_t));
    return rc;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_condpair_lock(mdbx_condpair_t *condpair) {
  #if defined(_WIN32) || defined(_WIN64)
    DWORD code = WaitForSingleObject(condpair->mutex, INFINITE);
    return waitstatus2errcode(code);
  #else
    return pthread_mutex_lock(&condpair->mutex);
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_condpair_unlock(mdbx_condpair_t *condpair) {
  #if defined(_WIN32) || defined(_WIN64)
    return ReleaseMutex(condpair->mutex) ? MDBX_SUCCESS : GetLastError();
  #else
    return pthread_mutex_unlock(&condpair->mutex);
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_condpair_signal(mdbx_condpair_t *condpair,
                                              bool part) {
  #if defined(_WIN32) || defined(_WIN64)
    return SetEvent(condpair->event[part]) ? MDBX_SUCCESS : GetLastError();
  #else
    return pthread_cond_signal(&condpair->cond[part]);
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_condpair_wait(mdbx_condpair_t *condpair,
                                            bool part) {
  #if defined(_WIN32) || defined(_WIN64)
    DWORD code = SignalObjectAndWait(condpair->mutex, condpair->event[part],
                                     INFINITE, FALSE);
    if (code == WAIT_OBJECT_0) {
      code = WaitForSingleObject(condpair->mutex, INFINITE);
      if (code == WAIT_OBJECT_0)
        return MDBX_SUCCESS;
    }
    return waitstatus2errcode(code);
  #else
    return pthread_cond_wait(&condpair->cond[part], &condpair->mutex);
  #endif
  }
  
  /*----------------------------------------------------------------------------*/
  
  MDBX_INTERNAL_FUNC int mdbx_fastmutex_init(mdbx_fastmutex_t *fastmutex) {
  #if defined(_WIN32) || defined(_WIN64)
    InitializeCriticalSection(fastmutex);
    return MDBX_SUCCESS;
  #else
    return pthread_mutex_init(fastmutex, NULL);
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_fastmutex_destroy(mdbx_fastmutex_t *fastmutex) {
  #if defined(_WIN32) || defined(_WIN64)
    DeleteCriticalSection(fastmutex);
    return MDBX_SUCCESS;
  #else
    return pthread_mutex_destroy(fastmutex);
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_fastmutex_acquire(mdbx_fastmutex_t *fastmutex) {
  #if defined(_WIN32) || defined(_WIN64)
    __try {
      EnterCriticalSection(fastmutex);
    } __except (
        (GetExceptionCode() ==
         0xC0000194 /* STATUS_POSSIBLE_DEADLOCK / EXCEPTION_POSSIBLE_DEADLOCK */)
            ? EXCEPTION_EXECUTE_HANDLER
            : EXCEPTION_CONTINUE_SEARCH) {
      return ERROR_POSSIBLE_DEADLOCK;
    }
    return MDBX_SUCCESS;
  #else
    return pthread_mutex_lock(fastmutex);
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_fastmutex_release(mdbx_fastmutex_t *fastmutex) {
  #if defined(_WIN32) || defined(_WIN64)
    LeaveCriticalSection(fastmutex);
    return MDBX_SUCCESS;
  #else
    return pthread_mutex_unlock(fastmutex);
  #endif
  }
  
  /*----------------------------------------------------------------------------*/
  
  MDBX_INTERNAL_FUNC int mdbx_removefile(const char *pathname) {
  #if defined(_WIN32) || defined(_WIN64)
    const size_t wlen = mbstowcs(nullptr, pathname, INT_MAX);
    if (wlen < 1 || wlen > /* MAX_PATH */ INT16_MAX)
      return ERROR_INVALID_NAME;
    wchar_t *const pathnameW = _alloca((wlen + 1) * sizeof(wchar_t));
    if (wlen != mbstowcs(pathnameW, pathname, wlen + 1))
      return ERROR_INVALID_NAME;
    return DeleteFileW(pathnameW) ? MDBX_SUCCESS : GetLastError();
  #else
    return unlink(pathname) ? errno : MDBX_SUCCESS;
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_removedirectory(const char *pathname) {
  #if defined(_WIN32) || defined(_WIN64)
    const size_t wlen = mbstowcs(nullptr, pathname, INT_MAX);
    if (wlen < 1 || wlen > /* MAX_PATH */ INT16_MAX)
      return ERROR_INVALID_NAME;
    wchar_t *const pathnameW = _alloca((wlen + 1) * sizeof(wchar_t));
    if (wlen != mbstowcs(pathnameW, pathname, wlen + 1))
      return ERROR_INVALID_NAME;
    return RemoveDirectoryW(pathnameW) ? MDBX_SUCCESS : GetLastError();
  #else
    return rmdir(pathname) ? errno : MDBX_SUCCESS;
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_openfile(const enum mdbx_openfile_purpose purpose,
                                       const MDBX_env *env, const char *pathname,
                                       mdbx_filehandle_t *fd,
                                       mdbx_mode_t unix_mode_bits) {
    *fd = INVALID_HANDLE_VALUE;
  
  #if defined(_WIN32) || defined(_WIN64)
    const size_t wlen = mbstowcs(nullptr, pathname, INT_MAX);
    if (wlen < 1 || wlen > /* MAX_PATH */ INT16_MAX)
      return ERROR_INVALID_NAME;
    wchar_t *const pathnameW = _alloca((wlen + 1) * sizeof(wchar_t));
    if (wlen != mbstowcs(pathnameW, pathname, wlen + 1))
      return ERROR_INVALID_NAME;
  
    DWORD CreationDisposition = unix_mode_bits ? OPEN_ALWAYS : OPEN_EXISTING;
    DWORD FlagsAndAttributes =
        FILE_FLAG_POSIX_SEMANTICS | FILE_ATTRIBUTE_NOT_CONTENT_INDEXED;
    DWORD DesiredAccess = FILE_READ_ATTRIBUTES;
    DWORD ShareMode = (env->me_flags & MDBX_EXCLUSIVE)
                          ? 0
                          : (FILE_SHARE_READ | FILE_SHARE_WRITE);
  
    switch (purpose) {
    default:
      return ERROR_INVALID_PARAMETER;
    case MDBX_OPEN_LCK:
      CreationDisposition = OPEN_ALWAYS;
      DesiredAccess |= GENERIC_READ | GENERIC_WRITE;
      FlagsAndAttributes |= FILE_ATTRIBUTE_HIDDEN | FILE_ATTRIBUTE_TEMPORARY;
      break;
    case MDBX_OPEN_DXB_READ:
      CreationDisposition = OPEN_EXISTING;
      DesiredAccess |= GENERIC_READ;
      ShareMode |= FILE_SHARE_READ;
      break;
    case MDBX_OPEN_DXB_LAZY:
      DesiredAccess |= GENERIC_READ | GENERIC_WRITE;
      break;
    case MDBX_OPEN_DXB_DSYNC:
      CreationDisposition = OPEN_EXISTING;
      DesiredAccess |= GENERIC_WRITE;
      FlagsAndAttributes |= FILE_FLAG_WRITE_THROUGH;
      break;
    case MDBX_OPEN_COPY:
      CreationDisposition = CREATE_NEW;
      ShareMode = 0;
      DesiredAccess |= GENERIC_WRITE;
      FlagsAndAttributes |=
          (env->me_psize < env->me_os_psize) ? 0 : FILE_FLAG_NO_BUFFERING;
      break;
    case MDBX_OPEN_DELETE:
      CreationDisposition = OPEN_EXISTING;
      ShareMode |= FILE_SHARE_DELETE;
      DesiredAccess =
          FILE_READ_ATTRIBUTES | FILE_WRITE_ATTRIBUTES | DELETE | SYNCHRONIZE;
      break;
    }
  
    *fd = CreateFileW(pathnameW, DesiredAccess, ShareMode, NULL,
                      CreationDisposition, FlagsAndAttributes, NULL);
    if (*fd == INVALID_HANDLE_VALUE)
      return GetLastError();
  
    BY_HANDLE_FILE_INFORMATION info;
    if (!GetFileInformationByHandle(*fd, &info)) {
      int err = GetLastError();
      CloseHandle(*fd);
      *fd = INVALID_HANDLE_VALUE;
      return err;
    }
    const DWORD AttributesDiff =
        (info.dwFileAttributes ^ FlagsAndAttributes) &
        (FILE_ATTRIBUTE_HIDDEN | FILE_ATTRIBUTE_NOT_CONTENT_INDEXED |
         FILE_ATTRIBUTE_TEMPORARY | FILE_ATTRIBUTE_COMPRESSED);
    if (AttributesDiff)
      (void)SetFileAttributesW(pathnameW, info.dwFileAttributes ^ AttributesDiff);
  
  #else
    int flags = unix_mode_bits ? O_CREAT : 0;
    switch (purpose) {
    default:
      return EINVAL;
    case MDBX_OPEN_LCK:
      flags |= O_RDWR;
      break;
    case MDBX_OPEN_DXB_READ:
      flags = O_RDONLY;
      break;
    case MDBX_OPEN_DXB_LAZY:
      flags |= O_RDWR;
      break;
    case MDBX_OPEN_COPY:
      flags = O_CREAT | O_WRONLY | O_EXCL;
      break;
    case MDBX_OPEN_DXB_DSYNC:
      flags |= O_WRONLY;
  #if defined(O_DSYNC)
      flags |= O_DSYNC;
  #elif defined(O_SYNC)
      flags |= O_SYNC;
  #elif defined(O_FSYNC)
      flags |= O_FSYNC;
  #endif
      break;
    case MDBX_OPEN_DELETE:
      flags = O_RDWR;
      break;
    }
  
    const bool direct_nocache_for_copy =
        env->me_psize >= env->me_os_psize && purpose == MDBX_OPEN_COPY;
    if (direct_nocache_for_copy) {
  #if defined(O_DIRECT)
      flags |= O_DIRECT;
  #endif /* O_DIRECT */
  #if defined(O_NOCACHE)
      flags |= O_NOCACHE;
  #endif /* O_NOCACHE */
    }
  
  #ifdef O_CLOEXEC
    flags |= O_CLOEXEC;
  #endif /* O_CLOEXEC */
  
    *fd = open(pathname, flags, unix_mode_bits);
  #if defined(O_DIRECT)
    if (*fd < 0 && (flags & O_DIRECT) &&
        (errno == EINVAL || errno == EAFNOSUPPORT)) {
      flags &= ~(O_DIRECT | O_EXCL);
      *fd = open(pathname, flags, unix_mode_bits);
    }
  #endif /* O_DIRECT */
    if (*fd < 0)
      return errno;
  
  #if defined(FD_CLOEXEC) && !defined(O_CLOEXEC)
    const int fd_flags = fcntl(*fd, F_GETFD);
    if (fd_flags != -1)
      (void)fcntl(*fd, F_SETFD, fd_flags | FD_CLOEXEC);
  #endif /* FD_CLOEXEC && !O_CLOEXEC */
  
    if (direct_nocache_for_copy) {
  #if defined(F_NOCACHE) && !defined(O_NOCACHE)
      (void)fcntl(*fd, F_NOCACHE, 1);
  #endif /* F_NOCACHE */
    }
  
  #endif
    return MDBX_SUCCESS;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_closefile(mdbx_filehandle_t fd) {
  #if defined(_WIN32) || defined(_WIN64)
    return CloseHandle(fd) ? MDBX_SUCCESS : GetLastError();
  #else
    return (close(fd) == 0) ? MDBX_SUCCESS : errno;
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_pread(mdbx_filehandle_t fd, void *buf, size_t bytes,
                                    uint64_t offset) {
    if (bytes > MAX_WRITE)
      return MDBX_EINVAL;
  #if defined(_WIN32) || defined(_WIN64)
    OVERLAPPED ov;
    ov.hEvent = 0;
    ov.Offset = (DWORD)offset;
    ov.OffsetHigh = HIGH_DWORD(offset);
  
    DWORD read = 0;
    if (unlikely(!ReadFile(fd, buf, (DWORD)bytes, &read, &ov))) {
      int rc = GetLastError();
      return (rc == MDBX_SUCCESS) ? /* paranoia */ ERROR_READ_FAULT : rc;
    }
  #else
    STATIC_ASSERT_MSG(sizeof(off_t) >= sizeof(size_t),
                      "libmdbx requires 64-bit file I/O on 64-bit systems");
    intptr_t read = pread(fd, buf, bytes, offset);
    if (read < 0) {
      int rc = errno;
      return (rc == MDBX_SUCCESS) ? /* paranoia */ MDBX_EIO : rc;
    }
  #endif
    return (bytes == (size_t)read) ? MDBX_SUCCESS : MDBX_ENODATA;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_pwrite(mdbx_filehandle_t fd, const void *buf,
                                     size_t bytes, uint64_t offset) {
    while (true) {
  #if defined(_WIN32) || defined(_WIN64)
      OVERLAPPED ov;
      ov.hEvent = 0;
      ov.Offset = (DWORD)offset;
      ov.OffsetHigh = HIGH_DWORD(offset);
  
      DWORD written;
      if (unlikely(!WriteFile(
              fd, buf, likely(bytes <= MAX_WRITE) ? (DWORD)bytes : MAX_WRITE,
              &written, &ov)))
        return GetLastError();
      if (likely(bytes == written))
        return MDBX_SUCCESS;
  #else
      STATIC_ASSERT_MSG(sizeof(off_t) >= sizeof(size_t),
                        "libmdbx requires 64-bit file I/O on 64-bit systems");
      const intptr_t written =
          pwrite(fd, buf, likely(bytes <= MAX_WRITE) ? bytes : MAX_WRITE, offset);
      if (likely(bytes == (size_t)written))
        return MDBX_SUCCESS;
      if (written < 0) {
        const int rc = errno;
        if (rc != EINTR)
          return rc;
        continue;
      }
  #endif
      bytes -= written;
      offset += written;
      buf = (char *)buf + written;
    }
  }
  
  MDBX_INTERNAL_FUNC int mdbx_write(mdbx_filehandle_t fd, const void *buf,
                                    size_t bytes) {
    while (true) {
  #if defined(_WIN32) || defined(_WIN64)
      DWORD written;
      if (unlikely(!WriteFile(
              fd, buf, likely(bytes <= MAX_WRITE) ? (DWORD)bytes : MAX_WRITE,
              &written, nullptr)))
        return GetLastError();
      if (likely(bytes == written))
        return MDBX_SUCCESS;
  #else
      STATIC_ASSERT_MSG(sizeof(off_t) >= sizeof(size_t),
                        "libmdbx requires 64-bit file I/O on 64-bit systems");
      const intptr_t written =
          write(fd, buf, likely(bytes <= MAX_WRITE) ? bytes : MAX_WRITE);
      if (likely(bytes == (size_t)written))
        return MDBX_SUCCESS;
      if (written < 0) {
        const int rc = errno;
        if (rc != EINTR)
          return rc;
        continue;
      }
  #endif
      bytes -= written;
      buf = (char *)buf + written;
    }
  }
  
  int mdbx_pwritev(mdbx_filehandle_t fd, struct iovec *iov, int iovcnt,
                   uint64_t offset, size_t expected_written) {
  #if defined(_WIN32) || defined(_WIN64) || defined(__APPLE__) ||                \
      (defined(__ANDROID_API__) && __ANDROID_API__ < 24)
    size_t written = 0;
    for (int i = 0; i < iovcnt; ++i) {
      int rc = mdbx_pwrite(fd, iov[i].iov_base, iov[i].iov_len, offset);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      written += iov[i].iov_len;
      offset += iov[i].iov_len;
    }
    return (expected_written == written) ? MDBX_SUCCESS
                                         : MDBX_EIO /* ERROR_WRITE_FAULT */;
  #else
    int rc;
    intptr_t written;
    do {
      STATIC_ASSERT_MSG(sizeof(off_t) >= sizeof(size_t),
                        "libmdbx requires 64-bit file I/O on 64-bit systems");
      written = pwritev(fd, iov, iovcnt, offset);
      if (likely(expected_written == (size_t)written))
        return MDBX_SUCCESS;
      rc = errno;
    } while (rc == EINTR);
    return (written < 0) ? rc : MDBX_EIO /* Use which error code? */;
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_fsync(mdbx_filehandle_t fd,
                                    enum mdbx_syncmode_bits mode_bits) {
  #if defined(_WIN32) || defined(_WIN64)
    if ((mode_bits & (MDBX_SYNC_DATA | MDBX_SYNC_IODQ)) && !FlushFileBuffers(fd))
      return GetLastError();
    return MDBX_SUCCESS;
  #else
  
  #if defined(__APPLE__) &&                                                      \
      MDBX_OSX_SPEED_INSTEADOF_DURABILITY == MDBX_OSX_WANNA_DURABILITY
    if (mode_bits & MDBX_SYNC_IODQ)
      return likely(fcntl(fd, F_FULLFSYNC) != -1) ? MDBX_SUCCESS : errno;
  #endif /* MacOS */
  
    /* LY: This approach is always safe and without appreciable performance
     * degradation, even on a kernel with fdatasync's bug.
     *
     * For more info about of a corresponding fdatasync() bug
     * see http://www.spinics.net/lists/linux-ext4/msg33714.html */
    while (1) {
      switch (mode_bits & (MDBX_SYNC_DATA | MDBX_SYNC_SIZE)) {
      case MDBX_SYNC_NONE:
        return MDBX_SUCCESS /* nothing to do */;
  #if defined(_POSIX_SYNCHRONIZED_IO) && _POSIX_SYNCHRONIZED_IO > 0
      case MDBX_SYNC_DATA:
        if (fdatasync(fd) == 0)
          return MDBX_SUCCESS;
        break /* error */;
  #if defined(__linux__) || defined(__gnu_linux__)
      case MDBX_SYNC_SIZE:
        if (mdbx_linux_kernel_version >= 0x03060000)
          return MDBX_SUCCESS;
        __fallthrough /* fall through */;
  #endif /* Linux */
  #endif /* _POSIX_SYNCHRONIZED_IO > 0 */
      default:
        if (fsync(fd) == 0)
          return MDBX_SUCCESS;
      }
  
      int rc = errno;
      if (rc != EINTR)
        return rc;
    }
  #endif
  }
  
  int mdbx_filesize(mdbx_filehandle_t fd, uint64_t *length) {
  #if defined(_WIN32) || defined(_WIN64)
    BY_HANDLE_FILE_INFORMATION info;
    if (!GetFileInformationByHandle(fd, &info))
      return GetLastError();
    *length = info.nFileSizeLow | (uint64_t)info.nFileSizeHigh << 32;
  #else
    struct stat st;
  
    STATIC_ASSERT_MSG(sizeof(off_t) <= sizeof(uint64_t),
                      "libmdbx requires 64-bit file I/O on 64-bit systems");
    if (fstat(fd, &st))
      return errno;
  
    *length = st.st_size;
  #endif
    return MDBX_SUCCESS;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_is_pipe(mdbx_filehandle_t fd) {
  #if defined(_WIN32) || defined(_WIN64)
    switch (GetFileType(fd)) {
    case FILE_TYPE_DISK:
      return MDBX_RESULT_FALSE;
    case FILE_TYPE_CHAR:
    case FILE_TYPE_PIPE:
      return MDBX_RESULT_TRUE;
    default:
      return GetLastError();
    }
  #else
    struct stat info;
    if (fstat(fd, &info))
      return errno;
    switch (info.st_mode & S_IFMT) {
    case S_IFBLK:
    case S_IFREG:
      return MDBX_RESULT_FALSE;
    case S_IFCHR:
    case S_IFIFO:
    case S_IFSOCK:
      return MDBX_RESULT_TRUE;
    case S_IFDIR:
    case S_IFLNK:
    default:
      return MDBX_INCOMPATIBLE;
    }
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_ftruncate(mdbx_filehandle_t fd, uint64_t length) {
  #if defined(_WIN32) || defined(_WIN64)
    if (mdbx_SetFileInformationByHandle) {
      FILE_END_OF_FILE_INFO EndOfFileInfo;
      EndOfFileInfo.EndOfFile.QuadPart = length;
      return mdbx_SetFileInformationByHandle(fd, FileEndOfFileInfo,
                                             &EndOfFileInfo,
                                             sizeof(FILE_END_OF_FILE_INFO))
                 ? MDBX_SUCCESS
                 : GetLastError();
    } else {
      LARGE_INTEGER li;
      li.QuadPart = length;
      return (SetFilePointerEx(fd, li, NULL, FILE_BEGIN) && SetEndOfFile(fd))
                 ? MDBX_SUCCESS
                 : GetLastError();
    }
  #else
    STATIC_ASSERT_MSG(sizeof(off_t) >= sizeof(size_t),
                      "libmdbx requires 64-bit file I/O on 64-bit systems");
    return ftruncate(fd, length) == 0 ? MDBX_SUCCESS : errno;
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_fseek(mdbx_filehandle_t fd, uint64_t pos) {
  #if defined(_WIN32) || defined(_WIN64)
    LARGE_INTEGER li;
    li.QuadPart = pos;
    return SetFilePointerEx(fd, li, NULL, FILE_BEGIN) ? MDBX_SUCCESS
                                                      : GetLastError();
  #else
    STATIC_ASSERT_MSG(sizeof(off_t) >= sizeof(size_t),
                      "libmdbx requires 64-bit file I/O on 64-bit systems");
    return (lseek(fd, pos, SEEK_SET) < 0) ? errno : MDBX_SUCCESS;
  #endif
  }
  
  /*----------------------------------------------------------------------------*/
  
  MDBX_INTERNAL_FUNC int
  mdbx_thread_create(mdbx_thread_t *thread,
                     THREAD_RESULT(THREAD_CALL *start_routine)(void *),
                     void *arg) {
  #if defined(_WIN32) || defined(_WIN64)
    *thread = CreateThread(NULL, 0, start_routine, arg, 0, NULL);
    return *thread ? MDBX_SUCCESS : GetLastError();
  #else
    return pthread_create(thread, NULL, start_routine, arg);
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_thread_join(mdbx_thread_t thread) {
  #if defined(_WIN32) || defined(_WIN64)
    DWORD code = WaitForSingleObject(thread, INFINITE);
    return waitstatus2errcode(code);
  #else
    void *unused_retval = &unused_retval;
    return pthread_join(thread, &unused_retval);
  #endif
  }
  
  /*----------------------------------------------------------------------------*/
  
  MDBX_INTERNAL_FUNC int mdbx_msync(mdbx_mmap_t *map, size_t offset,
                                    size_t length,
                                    enum mdbx_syncmode_bits mode_bits) {
    uint8_t *ptr = (uint8_t *)map->address + offset;
  #if defined(_WIN32) || defined(_WIN64)
    if (!FlushViewOfFile(ptr, length))
      return GetLastError();
  #else
  #if defined(__linux__) || defined(__gnu_linux__)
    if (mode_bits == MDBX_SYNC_NONE && mdbx_linux_kernel_version > 0x02061300)
      /* Since Linux 2.6.19, MS_ASYNC is in fact a no-op. The kernel properly
       * tracks dirty pages and flushes them to storage as necessary. */
      return MDBX_SUCCESS;
  #endif /* Linux */
    if (msync(ptr, length, (mode_bits & MDBX_SYNC_DATA) ? MS_SYNC : MS_ASYNC))
      return errno;
    mode_bits &= ~MDBX_SYNC_DATA;
  #endif
    return mdbx_fsync(map->fd, mode_bits);
  }
  
  MDBX_INTERNAL_FUNC int mdbx_check_fs_rdonly(mdbx_filehandle_t handle,
                                              const char *pathname, int err) {
  #if defined(_WIN32) || defined(_WIN64)
    (void)pathname;
    (void)err;
    if (!mdbx_GetVolumeInformationByHandleW)
      return MDBX_ENOSYS;
    DWORD unused, flags;
    if (!mdbx_GetVolumeInformationByHandleW(handle, nullptr, 0, nullptr, &unused,
                                            &flags, nullptr, 0))
      return GetLastError();
    if ((flags & FILE_READ_ONLY_VOLUME) == 0)
      return MDBX_EACCESS;
  #else
    struct statvfs info;
    if (err != MDBX_ENOFILE) {
      if (statvfs(pathname, &info))
        return errno;
      if ((info.f_flag & ST_RDONLY) == 0)
        return err;
    }
    if (fstatvfs(handle, &info))
      return errno;
    if ((info.f_flag & ST_RDONLY) == 0)
      return (err == MDBX_ENOFILE) ? MDBX_EACCESS : err;
  #endif /* !Windows */
    return MDBX_SUCCESS;
  }
  
  static int mdbx_check_fs_local(mdbx_filehandle_t handle, int flags) {
  #if defined(_WIN32) || defined(_WIN64)
    if (mdbx_RunningUnderWine() && !(flags & MDBX_EXCLUSIVE))
      return ERROR_NOT_CAPABLE /* workaround for Wine */;
  
    if (GetFileType(handle) != FILE_TYPE_DISK)
      return ERROR_FILE_OFFLINE;
  
    if (mdbx_GetFileInformationByHandleEx) {
      FILE_REMOTE_PROTOCOL_INFO RemoteProtocolInfo;
      if (mdbx_GetFileInformationByHandleEx(handle, FileRemoteProtocolInfo,
                                            &RemoteProtocolInfo,
                                            sizeof(RemoteProtocolInfo))) {
        if ((RemoteProtocolInfo.Flags & REMOTE_PROTOCOL_INFO_FLAG_OFFLINE) &&
            !(flags & MDBX_RDONLY))
          return ERROR_FILE_OFFLINE;
        if (!(RemoteProtocolInfo.Flags & REMOTE_PROTOCOL_INFO_FLAG_LOOPBACK) &&
            !(flags & MDBX_EXCLUSIVE))
          return ERROR_REMOTE_STORAGE_MEDIA_ERROR;
      }
    }
  
    if (mdbx_NtFsControlFile) {
      NTSTATUS rc;
      struct {
        WOF_EXTERNAL_INFO wof_info;
        union {
          WIM_PROVIDER_EXTERNAL_INFO wim_info;
          FILE_PROVIDER_EXTERNAL_INFO_V1 file_info;
        };
        size_t reserved_for_microsoft_madness[42];
      } GetExternalBacking_OutputBuffer;
      IO_STATUS_BLOCK StatusBlock;
      rc = mdbx_NtFsControlFile(handle, NULL, NULL, NULL, &StatusBlock,
                                FSCTL_GET_EXTERNAL_BACKING, NULL, 0,
                                &GetExternalBacking_OutputBuffer,
                                sizeof(GetExternalBacking_OutputBuffer));
      if (NT_SUCCESS(rc)) {
        if (!(flags & MDBX_EXCLUSIVE))
          return ERROR_REMOTE_STORAGE_MEDIA_ERROR;
      } else if (rc != STATUS_OBJECT_NOT_EXTERNALLY_BACKED &&
                 rc != STATUS_INVALID_DEVICE_REQUEST &&
                 rc != STATUS_NOT_SUPPORTED)
        return ntstatus2errcode(rc);
    }
  
    if (mdbx_GetVolumeInformationByHandleW && mdbx_GetFinalPathNameByHandleW) {
      WCHAR *PathBuffer = mdbx_malloc(sizeof(WCHAR) * INT16_MAX);
      if (!PathBuffer)
        return MDBX_ENOMEM;
  
      int rc = MDBX_SUCCESS;
      DWORD VolumeSerialNumber, FileSystemFlags;
      if (!mdbx_GetVolumeInformationByHandleW(handle, PathBuffer, INT16_MAX,
                                              &VolumeSerialNumber, NULL,
                                              &FileSystemFlags, NULL, 0)) {
        rc = GetLastError();
        goto bailout;
      }
  
      if ((flags & MDBX_RDONLY) == 0) {
        if (FileSystemFlags &
            (FILE_SEQUENTIAL_WRITE_ONCE | FILE_READ_ONLY_VOLUME |
             FILE_VOLUME_IS_COMPRESSED)) {
          rc = ERROR_REMOTE_STORAGE_MEDIA_ERROR;
          goto bailout;
        }
      }
  
      if (!mdbx_GetFinalPathNameByHandleW(handle, PathBuffer, INT16_MAX,
                                          FILE_NAME_NORMALIZED |
                                              VOLUME_NAME_NT)) {
        rc = GetLastError();
        goto bailout;
      }
  
      if (_wcsnicmp(PathBuffer, L"\\Device\\Mup\\", 12) == 0) {
        if (!(flags & MDBX_EXCLUSIVE)) {
          rc = ERROR_REMOTE_STORAGE_MEDIA_ERROR;
          goto bailout;
        }
      } else if (mdbx_GetFinalPathNameByHandleW(handle, PathBuffer, INT16_MAX,
                                                FILE_NAME_NORMALIZED |
                                                    VOLUME_NAME_DOS)) {
        UINT DriveType = GetDriveTypeW(PathBuffer);
        if (DriveType == DRIVE_NO_ROOT_DIR &&
            _wcsnicmp(PathBuffer, L"\\\\?\\", 4) == 0 &&
            _wcsnicmp(PathBuffer + 5, L":\\", 2) == 0) {
          PathBuffer[7] = 0;
          DriveType = GetDriveTypeW(PathBuffer + 4);
        }
        switch (DriveType) {
        case DRIVE_CDROM:
          if (flags & MDBX_RDONLY)
            break;
        // fall through
        case DRIVE_UNKNOWN:
        case DRIVE_NO_ROOT_DIR:
        case DRIVE_REMOTE:
        default:
          if (!(flags & MDBX_EXCLUSIVE))
            rc = ERROR_REMOTE_STORAGE_MEDIA_ERROR;
        // fall through
        case DRIVE_REMOVABLE:
        case DRIVE_FIXED:
        case DRIVE_RAMDISK:
          break;
        }
      }
    bailout:
      mdbx_free(PathBuffer);
      return rc;
    }
  
  #else
  
    struct statvfs statvfs_info;
    if (fstatvfs(handle, &statvfs_info))
      return errno;
  #if defined(ST_LOCAL) || defined(ST_EXPORTED)
    const unsigned long st_flags = statvfs_info.f_flag;
  #endif /* ST_LOCAL || ST_EXPORTED */
  
  #if defined(__NetBSD__)
    const unsigned type = 0;
    const char *const name = statvfs_info.f_fstypename;
    const size_t name_len = VFS_NAMELEN;
  #elif defined(_AIX) || defined(__OS400__)
    const char *const name = statvfs_info.f_basetype;
    const size_t name_len = sizeof(statvfs_info.f_basetype);
    struct stat st;
    if (fstat(handle, &st))
      return errno;
    const unsigned type = st.st_vfstype;
    if ((st.st_flag & FS_REMOTE) != 0 && !(flags & MDBX_EXCLUSIVE))
      return MDBX_EREMOTE;
  #elif defined(FSTYPSZ) || defined(_FSTYPSZ)
    const unsigned type = 0;
    const char *const name = statvfs_info.f_basetype;
    const size_t name_len = sizeof(statvfs_info.f_basetype);
  #elif defined(__sun) || defined(__SVR4) || defined(__svr4__) ||                \
      defined(ST_FSTYPSZ) || defined(_ST_FSTYPSZ)
    const unsigned type = 0;
    struct stat st;
    if (fstat(handle, &st))
      return errno;
    const char *const name = st.st_fstype;
    const size_t name_len = strlen(name);
  #else
    struct statfs statfs_info;
    if (fstatfs(handle, &statfs_info))
      return errno;
  #if defined(__OpenBSD__)
    const unsigned type = 0;
  #else
    const unsigned type = statfs_info.f_type;
  #endif
  #if defined(MNT_LOCAL) || defined(MNT_EXPORTED)
    const unsigned long mnt_flags = statfs_info.f_flags;
  #endif /* MNT_LOCAL || MNT_EXPORTED */
  #if defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) ||     \
      defined(__BSD__) || defined(__bsdi__) || defined(__DragonFly__) ||         \
      defined(__APPLE__) || defined(__MACH__) || defined(MFSNAMELEN) ||          \
      defined(MFSTYPENAMELEN) || defined(VFS_NAMELEN)
    const char *const name = statfs_info.f_fstypename;
    const size_t name_len = sizeof(statfs_info.f_fstypename);
  #elif defined(__ANDROID_API__) && __ANDROID_API__ < 21
    const char *const name = "";
    const unsigned name_len = 0;
  #else
  
    const char *name = "";
    unsigned name_len = 0;
  
    struct stat st;
    if (fstat(handle, &st))
      return errno;
  
    char pathbuf[PATH_MAX];
    FILE *mounted = nullptr;
  #if defined(__linux__) || defined(__gnu_linux__)
    mounted = setmntent("/proc/mounts", "r");
  #endif /* Linux */
    if (!mounted)
      mounted = setmntent("/etc/mtab", "r");
    if (mounted) {
      const struct mntent *ent;
  #if defined(_BSD_SOURCE) || defined(_SVID_SOURCE) || defined(__BIONIC__) ||    \
      (defined(_DEFAULT_SOURCE) && __GLIBC_PREREQ(2, 19))
      struct mntent entbuf;
      const bool should_copy = false;
      while (nullptr !=
             (ent = getmntent_r(mounted, &entbuf, pathbuf, sizeof(pathbuf))))
  #else
      const bool should_copy = true;
      while (nullptr != (ent = getmntent(mounted)))
  #endif
      {
        struct stat mnt;
        if (!stat(ent->mnt_dir, &mnt) && mnt.st_dev == st.st_dev) {
          if (should_copy) {
            name =
                strncpy(pathbuf, ent->mnt_fsname, name_len = sizeof(pathbuf) - 1);
            pathbuf[name_len] = 0;
          } else {
            name = ent->mnt_fsname;
            name_len = strlen(name);
          }
          break;
        }
      }
      endmntent(mounted);
    }
  #endif /* !xBSD && !Android/Bionic */
  #endif
  
    if (name_len) {
      if (((name_len > 2 && strncasecmp("nfs", name, 3) == 0) ||
           strncasecmp("cifs", name, name_len) == 0 ||
           strncasecmp("ncpfs", name, name_len) == 0 ||
           strncasecmp("smbfs", name, name_len) == 0 ||
           ((name_len > 3 && strncasecmp("fuse", name, 4) == 0) &&
            strncasecmp("fuseblk", name, name_len) != 0)) &&
          !(flags & MDBX_EXCLUSIVE))
        return MDBX_EREMOTE;
      if (strcasecmp("ftp", name) == 0 || strcasecmp("http", name) == 0 ||
          strcasecmp("sshfs", name) == 0)
        return MDBX_EREMOTE;
    }
  
  #ifdef ST_LOCAL
    if ((st_flags & ST_LOCAL) == 0 && !(flags & MDBX_EXCLUSIVE))
      return MDBX_EREMOTE;
  #elif defined(MNT_LOCAL)
    if ((mnt_flags & MNT_LOCAL) == 0 && !(flags & MDBX_EXCLUSIVE))
      return MDBX_EREMOTE;
  #endif /* ST/MNT_LOCAL */
  
  #ifdef ST_EXPORTED
    if ((st_flags & ST_EXPORTED) != 0 && !(flags & MDBX_RDONLY))
      return MDBX_EREMOTE;
  #elif defined(MNT_EXPORTED)
    if ((mnt_flags & MNT_EXPORTED) != 0 && !(flags & MDBX_RDONLY))
      return MDBX_EREMOTE;
  #endif /* ST/MNT_EXPORTED */
  
    switch (type) {
    case 0xFF534D42 /* CIFS_MAGIC_NUMBER */:
    case 0x6969 /* NFS_SUPER_MAGIC */:
    case 0x564c /* NCP_SUPER_MAGIC */:
    case 0x517B /* SMB_SUPER_MAGIC */:
  #if defined(__digital__) || defined(__osf__) || defined(__osf)
    case 0x0E /* Tru64 NFS */:
  #endif
  #ifdef ST_FST_NFS
    case ST_FST_NFS:
  #endif
      if ((flags & MDBX_EXCLUSIVE) == 0)
        return MDBX_EREMOTE;
    case 0:
    default:
      break;
    }
  #endif /* Unix */
  
    return MDBX_SUCCESS;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_mmap(const int flags, mdbx_mmap_t *map,
                                   const size_t size, const size_t limit,
                                   const unsigned options) {
    assert(size <= limit);
    map->limit = 0;
    map->current = 0;
    map->address = nullptr;
  #if defined(_WIN32) || defined(_WIN64)
    map->section = NULL;
    map->filesize = 0;
  #endif /* Windows */
  
    int err = mdbx_check_fs_local(map->fd, flags);
    if (unlikely(err != MDBX_SUCCESS))
      return err;
  
    if ((flags & MDBX_RDONLY) == 0 && (options & MMAP_OPTION_TRUNCATE) != 0) {
      err = mdbx_ftruncate(map->fd, size);
      if (err != MDBX_SUCCESS)
        return err;
  #if defined(_WIN32) || defined(_WIN64)
      map->filesize = size;
  #else
      map->current = size;
  #endif
    } else {
      uint64_t filesize = 0;
      err = mdbx_filesize(map->fd, &filesize);
      if (err != MDBX_SUCCESS)
        return err;
  #if defined(_WIN32) || defined(_WIN64)
      map->filesize = filesize;
  #else
      map->current = (filesize > limit) ? limit : (size_t)filesize;
  #endif
    }
  
  #if defined(_WIN32) || defined(_WIN64)
    LARGE_INTEGER SectionSize;
    SectionSize.QuadPart = size;
    err = NtCreateSection(
        &map->section,
        /* DesiredAccess */
        (flags & MDBX_WRITEMAP)
            ? SECTION_QUERY | SECTION_MAP_READ | SECTION_EXTEND_SIZE |
                  SECTION_MAP_WRITE
            : SECTION_QUERY | SECTION_MAP_READ | SECTION_EXTEND_SIZE,
        /* ObjectAttributes */ NULL, /* MaximumSize (InitialSize) */ &SectionSize,
        /* SectionPageProtection */
        (flags & MDBX_RDONLY) ? PAGE_READONLY : PAGE_READWRITE,
        /* AllocationAttributes */ SEC_RESERVE, map->fd);
    if (!NT_SUCCESS(err))
      return ntstatus2errcode(err);
  
    SIZE_T ViewSize =
        (flags & MDBX_RDONLY) ? 0 : mdbx_RunningUnderWine() ? size : limit;
    err = NtMapViewOfSection(
        map->section, GetCurrentProcess(), &map->address,
        /* ZeroBits */ 0,
        /* CommitSize */ 0,
        /* SectionOffset */ NULL, &ViewSize,
        /* InheritDisposition */ ViewUnmap,
        /* AllocationType */ (flags & MDBX_RDONLY) ? 0 : MEM_RESERVE,
        /* Win32Protect */
        (flags & MDBX_WRITEMAP) ? PAGE_READWRITE : PAGE_READONLY);
    if (!NT_SUCCESS(err)) {
      NtClose(map->section);
      map->section = 0;
      map->address = nullptr;
      return ntstatus2errcode(err);
    }
    assert(map->address != MAP_FAILED);
  
    map->current = (size_t)SectionSize.QuadPart;
    map->limit = ViewSize;
  
  #else
  
  #ifndef MAP_TRYFIXED
  #define MAP_TRYFIXED 0
  #endif
  
  #ifndef MAP_HASSEMAPHORE
  #define MAP_HASSEMAPHORE 0
  #endif
  
  #ifndef MAP_CONCEAL
  #define MAP_CONCEAL 0
  #endif
  
  #ifndef MAP_NOSYNC
  #define MAP_NOSYNC 0
  #endif
  
    map->address = mmap(
        NULL, limit, (flags & MDBX_WRITEMAP) ? PROT_READ | PROT_WRITE : PROT_READ,
        MAP_SHARED | MAP_FILE |
            (F_ISSET(flags, MDBX_UTTERLY_NOSYNC) ? MAP_NOSYNC : 0) |
            ((options & MMAP_OPTION_SEMAPHORE) ? MAP_HASSEMAPHORE | MAP_NOSYNC
                                               : MAP_CONCEAL),
        map->fd, 0);
  
    if (unlikely(map->address == MAP_FAILED)) {
      map->limit = 0;
      map->current = 0;
      map->address = nullptr;
      return errno;
    }
    map->limit = limit;
  
  #ifdef MADV_DONTFORK
    if (unlikely(madvise(map->address, map->limit, MADV_DONTFORK) != 0))
      return errno;
  #endif
  #ifdef MADV_NOHUGEPAGE
    (void)madvise(map->address, map->limit, MADV_NOHUGEPAGE);
  #endif
  
  #endif
  
    VALGRIND_MAKE_MEM_DEFINED(map->address, map->current);
    ASAN_UNPOISON_MEMORY_REGION(map->address, map->current);
    return MDBX_SUCCESS;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_munmap(mdbx_mmap_t *map) {
    VALGRIND_MAKE_MEM_NOACCESS(map->address, map->current);
    /* Unpoisoning is required for ASAN to avoid false-positive diagnostic
     * when this memory will re-used by malloc or another mmapping.
     * See https://github.com/erthink/libmdbx/pull/93#issuecomment-613687203 */
    ASAN_UNPOISON_MEMORY_REGION(map->address, map->limit);
  #if defined(_WIN32) || defined(_WIN64)
    if (map->section)
      NtClose(map->section);
    NTSTATUS rc = NtUnmapViewOfSection(GetCurrentProcess(), map->address);
    if (!NT_SUCCESS(rc))
      ntstatus2errcode(rc);
  #else
    if (unlikely(munmap(map->address, map->limit)))
      return errno;
  #endif
  
    map->limit = 0;
    map->current = 0;
    map->address = nullptr;
    return MDBX_SUCCESS;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_mresize(int flags, mdbx_mmap_t *map, size_t size,
                                      size_t limit, const bool may_move) {
    assert(size <= limit);
  #if defined(_WIN32) || defined(_WIN64)
    assert(size != map->current || limit != map->limit || size < map->filesize);
  
    NTSTATUS status;
    LARGE_INTEGER SectionSize;
    int err, rc = MDBX_SUCCESS;
  
    if (!(flags & MDBX_RDONLY) && limit == map->limit && size > map->current &&
        /* workaround for Wine */ mdbx_NtExtendSection) {
      /* growth rw-section */
      SectionSize.QuadPart = size;
      status = mdbx_NtExtendSection(map->section, &SectionSize);
      if (!NT_SUCCESS(status))
        return ntstatus2errcode(status);
      map->current = size;
      if (map->filesize < size)
        map->filesize = size;
      return MDBX_SUCCESS;
    }
  
    if (limit > map->limit) {
      /* check ability of address space for growth before unmap */
      PVOID BaseAddress = (PBYTE)map->address + map->limit;
      SIZE_T RegionSize = limit - map->limit;
      status = NtAllocateVirtualMemory(GetCurrentProcess(), &BaseAddress, 0,
                                       &RegionSize, MEM_RESERVE, PAGE_NOACCESS);
      if (status == /* STATUS_CONFLICTING_ADDRESSES */ 0xC0000018)
        return MDBX_UNABLE_EXTEND_MAPSIZE;
      if (!NT_SUCCESS(status))
        return ntstatus2errcode(status);
  
      status = NtFreeVirtualMemory(GetCurrentProcess(), &BaseAddress, &RegionSize,
                                   MEM_RELEASE);
      if (!NT_SUCCESS(status))
        return ntstatus2errcode(status);
    }
  
    /* Windows unable:
     *  - shrink a mapped file;
     *  - change size of mapped view;
     *  - extend read-only mapping;
     * Therefore we should unmap/map entire section. */
    status = NtUnmapViewOfSection(GetCurrentProcess(), map->address);
    if (!NT_SUCCESS(status))
      return ntstatus2errcode(status);
    status = NtClose(map->section);
    map->section = NULL;
    PVOID ReservedAddress = NULL;
    SIZE_T ReservedSize = limit;
  
    if (!NT_SUCCESS(status)) {
    bailout_ntstatus:
      err = ntstatus2errcode(status);
    bailout:
      map->address = NULL;
      map->current = map->limit = 0;
      if (ReservedAddress) {
        ReservedSize = 0;
        status = NtFreeVirtualMemory(GetCurrentProcess(), &ReservedAddress,
                                     &ReservedSize, MEM_RELEASE);
        assert(NT_SUCCESS(status));
        (void)status;
      }
      return err;
    }
  
  retry_file_and_section:
    /* resizing of the file may take a while,
     * therefore we reserve address space to avoid occupy it by other threads */
    ReservedAddress = map->address;
    status = NtAllocateVirtualMemory(GetCurrentProcess(), &ReservedAddress, 0,
                                     &ReservedSize, MEM_RESERVE, PAGE_NOACCESS);
    if (!NT_SUCCESS(status)) {
      ReservedAddress = NULL;
      if (status != /* STATUS_CONFLICTING_ADDRESSES */ 0xC0000018)
        goto bailout_ntstatus /* no way to recovery */;
  
      if (may_move)
        /* the base address could be changed */
        map->address = NULL;
    }
  
    err = mdbx_filesize(map->fd, &map->filesize);
    if (err != MDBX_SUCCESS)
      goto bailout;
  
    if ((flags & MDBX_RDONLY) == 0 && map->filesize != size) {
      err = mdbx_ftruncate(map->fd, size);
      if (err == MDBX_SUCCESS)
        map->filesize = size;
      /* ignore error, because Windows unable shrink file
       * that already mapped (by another process) */
    }
  
    SectionSize.QuadPart = size;
    status = NtCreateSection(
        &map->section,
        /* DesiredAccess */
        (flags & MDBX_WRITEMAP)
            ? SECTION_QUERY | SECTION_MAP_READ | SECTION_EXTEND_SIZE |
                  SECTION_MAP_WRITE
            : SECTION_QUERY | SECTION_MAP_READ | SECTION_EXTEND_SIZE,
        /* ObjectAttributes */ NULL,
        /* MaximumSize (InitialSize) */ &SectionSize,
        /* SectionPageProtection */
        (flags & MDBX_RDONLY) ? PAGE_READONLY : PAGE_READWRITE,
        /* AllocationAttributes */ SEC_RESERVE, map->fd);
  
    if (!NT_SUCCESS(status))
      goto bailout_ntstatus;
  
    if (ReservedAddress) {
      /* release reserved address space */
      ReservedSize = 0;
      status = NtFreeVirtualMemory(GetCurrentProcess(), &ReservedAddress,
                                   &ReservedSize, MEM_RELEASE);
      ReservedAddress = NULL;
      if (!NT_SUCCESS(status))
        goto bailout_ntstatus;
    }
  
  retry_mapview:;
    SIZE_T ViewSize = (flags & MDBX_RDONLY) ? size : limit;
    status = NtMapViewOfSection(
        map->section, GetCurrentProcess(), &map->address,
        /* ZeroBits */ 0,
        /* CommitSize */ 0,
        /* SectionOffset */ NULL, &ViewSize,
        /* InheritDisposition */ ViewUnmap,
        /* AllocationType */ (flags & MDBX_RDONLY) ? 0 : MEM_RESERVE,
        /* Win32Protect */
        (flags & MDBX_WRITEMAP) ? PAGE_READWRITE : PAGE_READONLY);
  
    if (!NT_SUCCESS(status)) {
      if (status == /* STATUS_CONFLICTING_ADDRESSES */ 0xC0000018 &&
          map->address && may_move) {
        /* try remap at another base address */
        map->address = NULL;
        goto retry_mapview;
      }
      NtClose(map->section);
      map->section = NULL;
  
      if (map->address && (size != map->current || limit != map->limit)) {
        /* try remap with previously size and limit,
         * but will return MDBX_UNABLE_EXTEND_MAPSIZE on success */
        rc = MDBX_UNABLE_EXTEND_MAPSIZE;
        size = map->current;
        ReservedSize = limit = map->limit;
        goto retry_file_and_section;
      }
  
      /* no way to recovery */
      goto bailout_ntstatus;
    }
    assert(map->address != MAP_FAILED);
  
    map->current = (size_t)SectionSize.QuadPart;
    map->limit = ViewSize;
  
  #else
  
    uint64_t filesize = 0;
    int rc = mdbx_filesize(map->fd, &filesize);
    if (rc != MDBX_SUCCESS)
      return rc;
  
    if (flags & MDBX_RDONLY) {
      map->current = (filesize > limit) ? limit : (size_t)filesize;
      if (map->current != size)
        rc = MDBX_UNABLE_EXTEND_MAPSIZE;
    } else if (filesize != size) {
      rc = mdbx_ftruncate(map->fd, size);
      if (rc != MDBX_SUCCESS)
        return rc;
      map->current = size;
    }
  
    if (limit == map->limit)
      return MDBX_SUCCESS;
  
    if (limit < map->limit) {
      /* unmap an excess at end of mapping. */
      if (unlikely(munmap(map->dxb + limit, map->limit - limit)))
        return errno;
      map->limit = limit;
      return MDBX_SUCCESS;
    }
  
    assert(limit > map->limit);
    uint8_t *ptr = MAP_FAILED;
  
  #if defined(MREMAP_MAYMOVE)
    ptr = mremap(map->address, map->limit, limit, may_move ? MREMAP_MAYMOVE : 0);
    if (ptr == MAP_FAILED) {
      const int err = errno;
      switch (err) {
      default:
        return err;
      case EAGAIN:
      case ENOMEM:
        return MDBX_UNABLE_EXTEND_MAPSIZE;
      case EFAULT /* MADV_DODUMP / MADV_DONTDUMP are mixed for mmap-range */:
        break;
      }
    }
  #endif /* MREMAP_MAYMOVE */
  
    const unsigned mmap_flags =
        MAP_CONCEAL | MAP_SHARED | MAP_FILE |
        (F_ISSET(flags, MDBX_UTTERLY_NOSYNC) ? MAP_NOSYNC : 0);
    const unsigned mmap_prot =
        (flags & MDBX_WRITEMAP) ? PROT_READ | PROT_WRITE : PROT_READ;
  
    if (ptr == MAP_FAILED) {
      /* Try to mmap additional space beyond the end of mapping. */
      ptr = mmap(map->dxb + map->limit, limit - map->limit, mmap_prot,
                 mmap_flags
  #if defined(MAP_FIXED_NOREPLACE)
                     | MAP_FIXED_NOREPLACE
  #endif /* MAP_FIXED_NOREPLACE */
                 ,
                 map->fd, map->limit);
      if (ptr == map->dxb + map->limit)
        ptr = map->dxb;
      else if (ptr != MAP_FAILED) {
        /* the desired address is busy, unmap unsuitable one */
        if (unlikely(munmap(ptr, limit - map->limit)))
          return errno;
        ptr = MAP_FAILED;
      } else {
        const int err = errno;
        switch (err) {
        default:
          return err;
        case EAGAIN:
        case ENOMEM:
          return MDBX_UNABLE_EXTEND_MAPSIZE;
        case EEXIST: /* address busy */
        case EINVAL: /* kernel don't support MAP_FIXED_NOREPLACE */
          break;
        }
      }
    }
  
    if (ptr == MAP_FAILED) {
      /* unmap and map again whole region */
      if (!may_move) {
        /* TODO: Perhaps here it is worth to implement suspend/resume threads
         * and perform unmap/map as like for Windows. */
        return MDBX_UNABLE_EXTEND_MAPSIZE;
      }
  
      if (unlikely(munmap(map->address, map->limit)))
        return errno;
  
      ptr = mmap(map->address, limit, mmap_prot, mmap_flags, map->fd, 0);
      if (unlikely(ptr == MAP_FAILED)) {
        ptr = mmap(map->address, map->limit, mmap_prot, mmap_flags, map->fd, 0);
        if (unlikely(ptr == MAP_FAILED)) {
          VALGRIND_MAKE_MEM_NOACCESS(map->address, map->current);
          /* Unpoisoning is required for ASAN to avoid false-positive diagnostic
           * when this memory will re-used by malloc or another mmapping.
           * See https://github.com/erthink/libmdbx/pull/93#issuecomment-613687203
           */
          ASAN_UNPOISON_MEMORY_REGION(map->address, map->limit);
          map->limit = 0;
          map->current = 0;
          map->address = nullptr;
          return errno;
        }
        rc = MDBX_UNABLE_EXTEND_MAPSIZE;
        limit = map->limit;
      }
    }
  
    assert(ptr && ptr != MAP_FAILED);
    if (map->address != ptr) {
      VALGRIND_MAKE_MEM_NOACCESS(map->address, map->current);
      /* Unpoisoning is required for ASAN to avoid false-positive diagnostic
       * when this memory will re-used by malloc or another mmapping.
       * See https://github.com/erthink/libmdbx/pull/93#issuecomment-613687203
       */
      ASAN_UNPOISON_MEMORY_REGION(map->address, map->limit);
  
      VALGRIND_MAKE_MEM_DEFINED(ptr, map->current);
      ASAN_UNPOISON_MEMORY_REGION(ptr, map->current);
      map->address = ptr;
    }
    map->limit = limit;
  
  #ifdef MADV_DONTFORK
    if (unlikely(madvise(map->address, map->limit, MADV_DONTFORK) != 0))
      return errno;
  #endif /* MADV_DONTFORK */
  
  #ifdef MADV_NOHUGEPAGE
    (void)madvise(map->address, map->limit, MADV_NOHUGEPAGE);
  #endif /* MADV_NOHUGEPAGE */
  
  #endif /* POSIX / Windows */
  
    return rc;
  }
  
  /*----------------------------------------------------------------------------*/
  
  MDBX_INTERNAL_FUNC __cold void mdbx_osal_jitter(bool tiny) {
    for (;;) {
  #if defined(_M_IX86) || defined(_M_X64) || defined(__i386__) ||                \
      defined(__x86_64__)
      const unsigned salt = 277u * (unsigned)__rdtsc();
  #else
      const unsigned salt = rand();
  #endif
  
      const unsigned coin = salt % (tiny ? 29u : 43u);
      if (coin < 43 / 3)
        break;
  #if defined(_WIN32) || defined(_WIN64)
      SwitchToThread();
      if (coin > 43 * 2 / 3)
        Sleep(1);
  #else
      sched_yield();
      if (coin > 43 * 2 / 3)
        usleep(coin);
  #endif
    }
  }
  
  #if defined(_WIN32) || defined(_WIN64)
  #elif defined(__APPLE__) || defined(__MACH__)
  #include <mach/mach_time.h>
  #elif defined(__linux__) || defined(__gnu_linux__)
  static __cold clockid_t choice_monoclock(void) {
    struct timespec probe;
  #if defined(CLOCK_BOOTTIME)
    if (clock_gettime(CLOCK_BOOTTIME, &probe) == 0)
      return CLOCK_BOOTTIME;
  #elif defined(CLOCK_MONOTONIC_RAW)
    if (clock_gettime(CLOCK_MONOTONIC_RAW, &probe) == 0)
      return CLOCK_MONOTONIC_RAW;
  #elif defined(CLOCK_MONOTONIC_COARSE)
    if (clock_gettime(CLOCK_MONOTONIC_COARSE, &probe) == 0)
      return CLOCK_MONOTONIC_COARSE;
  #endif
    return CLOCK_MONOTONIC;
  }
  #endif
  
  /*----------------------------------------------------------------------------*/
  
  #if defined(_WIN32) || defined(_WIN64)
  static LARGE_INTEGER performance_frequency;
  #elif defined(__APPLE__) || defined(__MACH__)
  static uint64_t ratio_16dot16_to_monotine;
  #endif
  
  MDBX_INTERNAL_FUNC uint64_t
  mdbx_osal_16dot16_to_monotime(uint32_t seconds_16dot16) {
  #if defined(_WIN32) || defined(_WIN64)
    if (unlikely(performance_frequency.QuadPart == 0))
      QueryPerformanceFrequency(&performance_frequency);
    const uint64_t ratio = performance_frequency.QuadPart;
  #elif defined(__APPLE__) || defined(__MACH__)
    if (unlikely(ratio_16dot16_to_monotine == 0)) {
      mach_timebase_info_data_t ti;
      mach_timebase_info(&ti);
      ratio_16dot16_to_monotine = UINT64_C(1000000000) * ti.denom / ti.numer;
    }
    const uint64_t ratio = ratio_16dot16_to_monotine;
  #else
    const uint64_t ratio = UINT64_C(1000000000);
  #endif
    return (ratio * seconds_16dot16 + 32768) >> 16;
  }
  
  MDBX_INTERNAL_FUNC uint32_t mdbx_osal_monotime_to_16dot16(uint64_t monotime) {
    static uint64_t limit;
    if (unlikely(monotime > limit)) {
      if (limit != 0)
        return UINT32_MAX;
      limit = mdbx_osal_16dot16_to_monotime(UINT32_MAX - 1);
      if (monotime > limit)
        return UINT32_MAX;
    }
  #if defined(_WIN32) || defined(_WIN64)
    return (uint32_t)((monotime << 16) / performance_frequency.QuadPart);
  #elif defined(__APPLE__) || defined(__MACH__)
    return (uint32_t)((monotime << 16) / ratio_16dot16_to_monotine);
  #else
    return (uint32_t)(monotime * 128 / 1953125);
  #endif
  }
  
  MDBX_INTERNAL_FUNC uint64_t mdbx_osal_monotime(void) {
  #if defined(_WIN32) || defined(_WIN64)
    LARGE_INTEGER counter;
    counter.QuadPart = 0;
    QueryPerformanceCounter(&counter);
    return counter.QuadPart;
  #elif defined(__APPLE__) || defined(__MACH__)
    return mach_absolute_time();
  #else
  
  #if defined(__linux__) || defined(__gnu_linux__)
    static clockid_t posix_clockid = -1;
    if (unlikely(posix_clockid < 0))
      posix_clockid = choice_monoclock();
  #elif defined(CLOCK_MONOTONIC)
  #define posix_clockid CLOCK_MONOTONIC
  #else
  #define posix_clockid CLOCK_REALTIME
  #endif
  
    struct timespec ts;
    if (unlikely(clock_gettime(posix_clockid, &ts) != 0)) {
      ts.tv_nsec = 0;
      ts.tv_sec = 0;
    }
    return ts.tv_sec * UINT64_C(1000000000) + ts.tv_nsec;
  #endif
  }
  
  /*----------------------------------------------------------------------------*/
  
  static void bootid_shake(bin128_t *p) {
    /* Bob Jenkins's PRNG: https://burtleburtle.net/bob/rand/smallprng.html */
    const uint32_t e = p->a - (p->b << 23 | p->b >> 9);
    p->a = p->b ^ (p->c << 16 | p->c >> 16);
    p->b = p->c + (p->d << 11 | p->d >> 21);
    p->c = p->d + e;
    p->d = e + p->a;
  }
  
  static void bootid_collect(bin128_t *p, const void *s, size_t n) {
    p->y += UINT64_C(64526882297375213);
    bootid_shake(p);
    for (size_t i = 0; i < n; ++i) {
      bootid_shake(p);
      p->y ^= UINT64_C(48797879452804441) * ((const uint8_t *)s)[i];
      bootid_shake(p);
      p->y += 14621231;
    }
    bootid_shake(p);
  
    /* minor non-linear tomfoolery */
    const unsigned z = p->x % 61;
    p->y = p->y << z | p->y >> (64 - z);
    bootid_shake(p);
    bootid_shake(p);
    const unsigned q = p->x % 59;
    p->y = p->y << q | p->y >> (64 - q);
    bootid_shake(p);
    bootid_shake(p);
    bootid_shake(p);
  }
  
  #if defined(_WIN32) || defined(_WIN64)
  
  static uint64_t windows_systemtime_ms() {
    FILETIME ft;
    GetSystemTimeAsFileTime(&ft);
    return ((uint64_t)ft.dwHighDateTime << 32 | ft.dwLowDateTime) / 10000ul;
  }
  
  static uint64_t windows_bootime(void) {
    unsigned confirmed = 0;
    uint64_t boottime = 0;
    uint64_t up0 = mdbx_GetTickCount64();
    uint64_t st0 = windows_systemtime_ms();
    for (uint64_t fuse = st0; up0 && st0 < fuse + 1000 * 1000u / 42;) {
      YieldProcessor();
      const uint64_t up1 = mdbx_GetTickCount64();
      const uint64_t st1 = windows_systemtime_ms();
      if (st1 > fuse && st1 == st0 && up1 == up0) {
        uint64_t diff = st1 - up1;
        if (boottime == diff) {
          if (++confirmed > 4)
            return boottime;
        } else {
          confirmed = 0;
          boottime = diff;
        }
        fuse = st1;
        Sleep(1);
      }
      st0 = st1;
      up0 = up1;
    }
    return 0;
  }
  
  static LSTATUS mdbx_RegGetValue(HKEY hKey, LPCSTR lpSubKey, LPCSTR lpValue,
                                  PVOID pvData, LPDWORD pcbData) {
    LSTATUS rc;
    if (!mdbx_RegGetValueA) {
      /* an old Windows 2000/XP */
      HKEY hSubKey;
      rc = RegOpenKeyA(hKey, lpSubKey, &hSubKey);
      if (rc == ERROR_SUCCESS) {
        rc = RegQueryValueExA(hSubKey, lpValue, NULL, NULL, pvData, pcbData);
        RegCloseKey(hSubKey);
      }
      return rc;
    }
  
    rc = mdbx_RegGetValueA(hKey, lpSubKey, lpValue, RRF_RT_ANY, NULL, pvData,
                           pcbData);
    if (rc != ERROR_FILE_NOT_FOUND)
      return rc;
  
    rc = mdbx_RegGetValueA(hKey, lpSubKey, lpValue,
                           RRF_RT_ANY | 0x00010000 /* RRF_SUBKEY_WOW6464KEY */,
                           NULL, pvData, pcbData);
    if (rc != ERROR_FILE_NOT_FOUND)
      return rc;
    return mdbx_RegGetValueA(hKey, lpSubKey, lpValue,
                             RRF_RT_ANY | 0x00020000 /* RRF_SUBKEY_WOW6432KEY */,
                             NULL, pvData, pcbData);
  }
  #endif
  
  static __cold __maybe_unused bool bootid_parse_uuid(bin128_t *s, const void *p,
                                                      const size_t n) {
    if (n > 31) {
      unsigned bits = 0;
      for (unsigned i = 0; i < n; ++i) /* try parse an UUID in text form */ {
        uint8_t c = ((const uint8_t *)p)[i];
        if (c >= '0' && c <= '9')
          c -= '0';
        else if (c >= 'a' && c <= 'f')
          c -= 'a' - 10;
        else if (c >= 'A' && c <= 'F')
          c -= 'A' - 10;
        else
          continue;
        assert(c <= 15);
        c ^= s->y >> 60;
        s->y = s->y << 4 | s->x >> 60;
        s->x = s->x << 4 | c;
        bits += 4;
      }
      if (bits > 42 * 3)
        /* UUID parsed successfully */
        return true;
    }
  
    if (n > 15) /* is enough handle it as a binary? */ {
      if (n == sizeof(bin128_t)) {
        bin128_t aligned;
        memcpy(&aligned, p, sizeof(bin128_t));
        s->x += aligned.x;
        s->y += aligned.y;
      } else
        bootid_collect(s, p, n);
      return true;
    }
  
    if (n)
      bootid_collect(s, p, n);
    return false;
  }
  
  __cold MDBX_INTERNAL_FUNC bin128_t mdbx_osal_bootid(void) {
    bin128_t bin = {{0, 0}};
    bool got_machineid = false, got_boottime = false, got_bootseq = false;
  
  #if defined(__linux__) || defined(__gnu_linux__)
    {
      const int fd =
          open("/proc/sys/kernel/random/boot_id", O_RDONLY | O_NOFOLLOW);
      if (fd != -1) {
        struct statfs fs;
        char buf[42];
        const ssize_t len =
            (fstatfs(fd, &fs) == 0 && fs.f_type == /* procfs */ 0x9FA0)
                ? read(fd, buf, sizeof(buf))
                : -1;
        const int err = close(fd);
        assert(err == 0);
        (void)err;
        if (len > 0 && bootid_parse_uuid(&bin, buf, len))
          return bin;
      }
    }
  #endif /* Linux */
  
  #if defined(__APPLE__) || defined(__MACH__)
    {
      char buf[42];
      size_t len = sizeof(buf);
      if (!sysctlbyname("kern.bootsessionuuid", buf, &len, nullptr, 0) &&
          bootid_parse_uuid(&bin, buf, len))
        return bin;
  
  #if defined(__MAC_OS_X_VERSION_MIN_REQUIRED) &&                                \
      __MAC_OS_X_VERSION_MIN_REQUIRED > 1050
      uuid_t uuid;
      struct timespec wait = {0, 1000000000u / 42};
      if (!gethostuuid(uuid, &wait) &&
          bootid_parse_uuid(&bin, uuid, sizeof(uuid)))
        got_machineid = true;
  #endif /* > 10.5 */
  
      struct timeval boottime;
      len = sizeof(boottime);
      if (!sysctlbyname("kern.boottime", &boottime, &len, nullptr, 0) &&
          len == sizeof(boottime) && boottime.tv_sec)
        got_boottime = true;
    }
  #endif /* Apple/Darwin */
  
  #if defined(_WIN32) || defined(_WIN64)
    {
      union buf {
        DWORD BootId;
        DWORD BaseTime;
        SYSTEM_TIMEOFDAY_INFORMATION SysTimeOfDayInfo;
        struct {
          LARGE_INTEGER BootTime;
          LARGE_INTEGER CurrentTime;
          LARGE_INTEGER TimeZoneBias;
          ULONG TimeZoneId;
          ULONG Reserved;
          ULONGLONG BootTimeBias;
          ULONGLONG SleepTimeBias;
        } SysTimeOfDayInfoHacked;
        wchar_t MachineGuid[42];
        char DigitalProductId[248];
      } buf;
  
      static const char HKLM_MicrosoftCryptography[] =
          "SOFTWARE\\Microsoft\\Cryptography";
      DWORD len = sizeof(buf);
      /* Windows is madness and must die */
      if (mdbx_RegGetValue(HKEY_LOCAL_MACHINE, HKLM_MicrosoftCryptography,
                           "MachineGuid", &buf.MachineGuid,
                           &len) == ERROR_SUCCESS &&
          len > 42 && len < sizeof(buf))
        got_machineid = bootid_parse_uuid(&bin, &buf.MachineGuid, len);
  
      if (!got_machineid) {
        /* again, Windows is madness */
        static const char HKLM_WindowsNT[] =
            "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion";
        static const char HKLM_WindowsNT_DPK[] =
            "SOFTWARE\\Microsoft\\Windows "
            "NT\\CurrentVersion\\DefaultProductKey";
        static const char HKLM_WindowsNT_DPK2[] =
            "SOFTWARE\\Microsoft\\Windows "
            "NT\\CurrentVersion\\DefaultProductKey2";
  
        len = sizeof(buf);
        if (mdbx_RegGetValue(HKEY_LOCAL_MACHINE, HKLM_WindowsNT,
                             "DigitalProductId", &buf.DigitalProductId,
                             &len) == ERROR_SUCCESS &&
            len > 42 && len < sizeof(buf)) {
          bootid_collect(&bin, &buf.DigitalProductId, len);
          got_machineid = true;
        }
        len = sizeof(buf);
        if (mdbx_RegGetValue(HKEY_LOCAL_MACHINE, HKLM_WindowsNT_DPK,
                             "DigitalProductId", &buf.DigitalProductId,
                             &len) == ERROR_SUCCESS &&
            len > 42 && len < sizeof(buf)) {
          bootid_collect(&bin, &buf.DigitalProductId, len);
          got_machineid = true;
        }
        len = sizeof(buf);
        if (mdbx_RegGetValue(HKEY_LOCAL_MACHINE, HKLM_WindowsNT_DPK2,
                             "DigitalProductId", &buf.DigitalProductId,
                             &len) == ERROR_SUCCESS &&
            len > 42 && len < sizeof(buf)) {
          bootid_collect(&bin, &buf.DigitalProductId, len);
          got_machineid = true;
        }
      }
  
      static const char HKLM_PrefetcherParams[] =
          "SYSTEM\\CurrentControlSet\\Control\\Session Manager\\Memory "
          "Management\\PrefetchParameters";
      len = sizeof(buf);
      if (mdbx_RegGetValue(HKEY_LOCAL_MACHINE, HKLM_PrefetcherParams, "BootId",
                           &buf.BootId, &len) == ERROR_SUCCESS &&
          len > 1 && len < sizeof(buf)) {
        bootid_collect(&bin, &buf.BootId, len);
        got_bootseq = true;
      }
  
      len = sizeof(buf);
      if (mdbx_RegGetValue(HKEY_LOCAL_MACHINE, HKLM_PrefetcherParams, "BaseTime",
                           &buf.BaseTime, &len) == ERROR_SUCCESS &&
          len >= sizeof(buf.BaseTime) && buf.BaseTime) {
        bootid_collect(&bin, &buf.BaseTime, len);
        got_boottime = true;
      }
  
      /* BootTime from SYSTEM_TIMEOFDAY_INFORMATION */
      NTSTATUS status = NtQuerySystemInformation(
          0x03 /* SystemTmeOfDayInformation */, &buf.SysTimeOfDayInfo,
          sizeof(buf.SysTimeOfDayInfo), &len);
      if (NT_SUCCESS(status) &&
          len >= offsetof(union buf, SysTimeOfDayInfoHacked.BootTime) +
                     sizeof(buf.SysTimeOfDayInfoHacked.BootTime) &&
          buf.SysTimeOfDayInfoHacked.BootTime.QuadPart) {
        bootid_collect(&bin, &buf.SysTimeOfDayInfoHacked.BootTime,
                       sizeof(buf.SysTimeOfDayInfoHacked.BootTime));
        got_boottime = true;
      }
  
      if (!got_boottime) {
        uint64_t boottime = windows_bootime();
        if (boottime) {
          bootid_collect(&bin, &boottime, sizeof(boottime));
          got_boottime = true;
        }
      }
    }
  #endif /* Windows */
  
  #if defined(CTL_HW) && defined(HW_UUID)
    if (!got_machineid) {
      static const int mib[] = {CTL_HW, HW_UUID};
      char buf[42];
      size_t len = sizeof(buf);
      if (sysctl(
  #ifdef SYSCTL_LEGACY_NONCONST_MIB
              (int *)
  #endif
                  mib,
              ARRAY_LENGTH(mib), &buf, &len, NULL, 0) == 0)
        got_machineid = bootid_parse_uuid(&bin, buf, len);
    }
  #endif /* CTL_HW && HW_UUID */
  
  #if defined(CTL_KERN) && defined(KERN_HOSTUUID)
    if (!got_machineid) {
      static const int mib[] = {CTL_KERN, KERN_HOSTUUID};
      char buf[42];
      size_t len = sizeof(buf);
      if (sysctl(
  #ifdef SYSCTL_LEGACY_NONCONST_MIB
              (int *)
  #endif
                  mib,
              ARRAY_LENGTH(mib), &buf, &len, NULL, 0) == 0)
        got_machineid = bootid_parse_uuid(&bin, buf, len);
    }
  #endif /* CTL_KERN && KERN_HOSTUUID */
  
  #if defined(__NetBSD__)
    if (!got_machineid) {
      char buf[42];
      size_t len = sizeof(buf);
      if (sysctlbyname("machdep.dmi.system-uuid", buf, &len, NULL, 0) == 0)
        got_machineid = bootid_parse_uuid(&bin, buf, len);
    }
  #endif /* __NetBSD__ */
  
  #if _XOPEN_SOURCE_EXTENDED
    if (!got_machineid) {
      const int hostid = gethostid();
      if (hostid > 0) {
        bootid_collect(&bin, &hostid, sizeof(hostid));
        got_machineid = true;
      }
    }
  #endif /* _XOPEN_SOURCE_EXTENDED */
  
    if (!got_machineid) {
    lack:
      bin.x = bin.y = 0;
      return bin;
    }
  
    /*--------------------------------------------------------------------------*/
  
  #if defined(CTL_KERN) && defined(KERN_BOOTTIME)
    if (!got_boottime) {
      static const int mib[] = {CTL_KERN, KERN_BOOTTIME};
      struct timeval boottime;
      size_t len = sizeof(boottime);
      if (sysctl(
  #ifdef SYSCTL_LEGACY_NONCONST_MIB
              (int *)
  #endif
                  mib,
              ARRAY_LENGTH(mib), &boottime, &len, NULL, 0) == 0 &&
          len == sizeof(boottime) && boottime.tv_sec) {
        bootid_collect(&bin, &boottime, len);
        got_boottime = true;
      }
    }
  #endif /* CTL_KERN && KERN_BOOTTIME */
  
  #if defined(__sun) || defined(__SVR4) || defined(__svr4__)
    if (!got_boottime) {
      kstat_ctl_t *kc = kstat_open();
      if (kc) {
        kstat_t *kp = kstat_lookup(kc, "unix", 0, "system_misc");
        if (kp && kstat_read(kc, kp, 0) != -1) {
          kstat_named_t *kn = (kstat_named_t *)kstat_data_lookup(kp, "boot_time");
          if (kn) {
            switch (kn->data_type) {
            case KSTAT_DATA_INT32:
            case KSTAT_DATA_UINT32:
              bootid_collect(&bin, &kn->value, sizeof(int32_t));
              got_boottime = true;
            case KSTAT_DATA_INT64:
            case KSTAT_DATA_UINT64:
              bootid_collect(&bin, &kn->value, sizeof(int64_t));
              got_boottime = true;
            }
          }
        }
        kstat_close(kc);
      }
    }
  #endif /* SunOS / Solaris */
  
  #if _XOPEN_SOURCE_EXTENDED && defined(BOOT_TIME)
    if (!got_boottime) {
      setutxent();
      const struct utmpx id = {.ut_type = BOOT_TIME};
      const struct utmpx *entry = getutxid(&id);
      if (entry) {
        bootid_collect(&bin, entry, sizeof(*entry));
        got_boottime = true;
        while (unlikely((entry = getutxid(&id)) != nullptr)) {
          /* have multiple reboot records, assuming we can distinguish next
           * bootsession even if RTC is wrong or absent */
          bootid_collect(&bin, entry, sizeof(*entry));
          got_bootseq = true;
        }
      }
      endutxent();
    }
  #endif /* _XOPEN_SOURCE_EXTENDED && BOOT_TIME */
  
    if (!got_bootseq) {
      if (!got_boottime || !MDBX_TRUST_RTC)
        goto lack;
  
  #if defined(_WIN32) || defined(_WIN64)
      FILETIME now;
      GetSystemTimeAsFileTime(&now);
      if (0x1CCCCCC > now.dwHighDateTime)
  #else
      struct timespec mono, real;
      if (clock_gettime(CLOCK_MONOTONIC, &mono) ||
          clock_gettime(CLOCK_REALTIME, &real) ||
          /* wrong time, RTC is mad or absent */
          1555555555l > real.tv_sec ||
          /* seems no adjustment by RTC/NTP, i.e. a fake time */
          real.tv_sec < mono.tv_sec || 1234567890l > real.tv_sec - mono.tv_sec ||
          (real.tv_sec - mono.tv_sec) % 900u == 0)
  #endif
        goto lack;
    }
  
    return bin;
  }
  /* This is CMake-template for libmdbx's version.c
   ******************************************************************************/
  
  
  #if MDBX_VERSION_MAJOR != 0 ||                             \
      MDBX_VERSION_MINOR != 9
  #error "API version mismatch! Had `git fetch --tags` done?"
  #endif
  
  static const char sourcery[] = STRINGIFY(MDBX_BUILD_SOURCERY);
  
  __dll_export
  #ifdef __attribute_used__
      __attribute_used__
  #elif defined(__GNUC__) || __has_attribute(__used__)
      __attribute__((__used__))
  #endif
  #ifdef __attribute_externally_visible__
          __attribute_externally_visible__
  #elif (defined(__GNUC__) && !defined(__clang__)) ||                            \
      __has_attribute(__externally_visible__)
      __attribute__((__externally_visible__))
  #endif
      const struct MDBX_version_info mdbx_version = {
          0,
          9,
          2,
          21,
          {"2021-01-06T14:20:03-08:00", "5d7c69a7b3d8215d35038c374e17eb3ae5b8e67c", "1c708147b76afad67eb929139f456d0c03df52ed",
           "v0.9.2-21-g1c70814"},
          sourcery};
  
  __dll_export
  #ifdef __attribute_used__
      __attribute_used__
  #elif defined(__GNUC__) || __has_attribute(__used__)
      __attribute__((__used__))
  #endif
  #ifdef __attribute_externally_visible__
          __attribute_externally_visible__
  #elif (defined(__GNUC__) && !defined(__clang__)) ||                            \
      __has_attribute(__externally_visible__)
      __attribute__((__externally_visible__))
  #endif
      const char *const mdbx_sourcery_anchor = sourcery;
  /*
   * Copyright 2015-2020 Leonid Yuriev <leo@yuriev.ru>
   * and other libmdbx authors: please see AUTHORS file.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted only as authorized by the OpenLDAP
   * Public License.
   *
   * A copy of this license is available in the file LICENSE in the
   * top-level directory of the distribution or, alternatively, at
   * <http://www.OpenLDAP.org/license.html>.
   */
  
  #if defined(_WIN32) || defined(_WIN64) /* Windows LCK-implementation */
  
  /* PREAMBLE FOR WINDOWS:
   *
   * We are not concerned for performance here.
   * If you are running Windows a performance could NOT be the goal.
   * Otherwise please use Linux. */
  
  
  static void mdbx_winnt_import(void);
  
  #if MDBX_BUILD_SHARED_LIBRARY
  #if MDBX_AVOID_CRT && defined(NDEBUG)
  /* DEBUG/CHECKED builds still require MSVC's CRT for runtime checks.
   *
   * Define dll's entry point only for Release build when NDEBUG is defined and
   * MDBX_AVOID_CRT=ON. if the entry point isn't defined then MSVC's will
   * automatically use DllMainCRTStartup() from CRT library, which also
   * automatically call DllMain() from our mdbx.dll */
  #pragma comment(linker, "/ENTRY:DllMain")
  #endif /* MDBX_AVOID_CRT */
  
  BOOL APIENTRY DllMain(HANDLE module, DWORD reason, LPVOID reserved)
  #else
  #if !MDBX_CONFIG_MANUAL_TLS_CALLBACK
  static
  #endif /* !MDBX_CONFIG_MANUAL_TLS_CALLBACK */
      void NTAPI
      mdbx_dll_handler(PVOID module, DWORD reason, PVOID reserved)
  #endif /* MDBX_BUILD_SHARED_LIBRARY */
  {
    (void)reserved;
    switch (reason) {
    case DLL_PROCESS_ATTACH:
      mdbx_winnt_import();
      mdbx_rthc_global_init();
      break;
    case DLL_PROCESS_DETACH:
      mdbx_rthc_global_dtor();
      break;
  
    case DLL_THREAD_ATTACH:
      break;
    case DLL_THREAD_DETACH:
      mdbx_rthc_thread_dtor(module);
      break;
    }
  #if MDBX_BUILD_SHARED_LIBRARY
    return TRUE;
  #endif
  }
  
  #if !MDBX_BUILD_SHARED_LIBRARY && !MDBX_CONFIG_MANUAL_TLS_CALLBACK
  /* *INDENT-OFF* */
  /* clang-format off */
  #if defined(_MSC_VER)
  #  pragma const_seg(push)
  #  pragma data_seg(push)
  
  #  ifdef _WIN64
       /* kick a linker to create the TLS directory if not already done */
  #    pragma comment(linker, "/INCLUDE:_tls_used")
       /* Force some symbol references. */
  #    pragma comment(linker, "/INCLUDE:mdbx_tls_anchor")
       /* specific const-segment for WIN64 */
  #    pragma const_seg(".CRT$XLB")
       const
  #  else
       /* kick a linker to create the TLS directory if not already done */
  #    pragma comment(linker, "/INCLUDE:__tls_used")
       /* Force some symbol references. */
  #    pragma comment(linker, "/INCLUDE:_mdbx_tls_anchor")
       /* specific data-segment for WIN32 */
  #    pragma data_seg(".CRT$XLB")
  #  endif
  
     __declspec(allocate(".CRT$XLB")) PIMAGE_TLS_CALLBACK mdbx_tls_anchor = mdbx_dll_handler;
  #  pragma data_seg(pop)
  #  pragma const_seg(pop)
  
  #elif defined(__GNUC__)
  #  ifdef _WIN64
       const
  #  endif
     PIMAGE_TLS_CALLBACK mdbx_tls_anchor __attribute__((__section__(".CRT$XLB"), used)) = mdbx_dll_handler;
  #else
  #  error FIXME
  #endif
  /* *INDENT-ON* */
  /* clang-format on */
  #endif /* !MDBX_BUILD_SHARED_LIBRARY && !MDBX_CONFIG_MANUAL_TLS_CALLBACK */
  
  /*----------------------------------------------------------------------------*/
  
  #define LCK_SHARED 0
  #define LCK_EXCLUSIVE LOCKFILE_EXCLUSIVE_LOCK
  #define LCK_WAITFOR 0
  #define LCK_DONTWAIT LOCKFILE_FAIL_IMMEDIATELY
  
  static __inline BOOL flock(mdbx_filehandle_t fd, DWORD flags, uint64_t offset,
                             size_t bytes) {
    OVERLAPPED ov;
    ov.hEvent = 0;
    ov.Offset = (DWORD)offset;
    ov.OffsetHigh = HIGH_DWORD(offset);
    return LockFileEx(fd, flags, 0, (DWORD)bytes, HIGH_DWORD(bytes), &ov);
  }
  
  static __inline BOOL funlock(mdbx_filehandle_t fd, uint64_t offset,
                               size_t bytes) {
    return UnlockFile(fd, (DWORD)offset, HIGH_DWORD(offset), (DWORD)bytes,
                      HIGH_DWORD(bytes));
  }
  
  /*----------------------------------------------------------------------------*/
  /* global `write` lock for write-txt processing,
   * exclusive locking both meta-pages) */
  
  #define LCK_MAXLEN (1u + (size_t)(MAXSSIZE_T))
  #define LCK_META_OFFSET 0
  #define LCK_META_LEN (MAX_PAGESIZE * NUM_METAS)
  #define LCK_BODY_OFFSET LCK_META_LEN
  #define LCK_BODY_LEN (LCK_MAXLEN - LCK_BODY_OFFSET)
  #define LCK_BODY LCK_BODY_OFFSET, LCK_BODY_LEN
  #define LCK_WHOLE 0, LCK_MAXLEN
  
  int mdbx_txn_lock(MDBX_env *env, bool dontwait) {
    if (dontwait) {
      if (!TryEnterCriticalSection(&env->me_windowsbug_lock))
        return MDBX_BUSY;
    } else {
      __try {
        EnterCriticalSection(&env->me_windowsbug_lock);
      }
      __except ((GetExceptionCode() ==
                   0xC0000194 /* STATUS_POSSIBLE_DEADLOCK / EXCEPTION_POSSIBLE_DEADLOCK */)
                      ? EXCEPTION_EXECUTE_HANDLER
                      : EXCEPTION_CONTINUE_SEARCH) {
        return ERROR_POSSIBLE_DEADLOCK;
      }
    }
  
    if ((env->me_flags & MDBX_EXCLUSIVE) ||
        flock(env->me_lazy_fd,
              dontwait ? (LCK_EXCLUSIVE | LCK_DONTWAIT)
                       : (LCK_EXCLUSIVE | LCK_WAITFOR),
              LCK_BODY))
      return MDBX_SUCCESS;
    int rc = GetLastError();
    LeaveCriticalSection(&env->me_windowsbug_lock);
    return (!dontwait || rc != ERROR_LOCK_VIOLATION) ? rc : MDBX_BUSY;
  }
  
  void mdbx_txn_unlock(MDBX_env *env) {
    int rc = (env->me_flags & MDBX_EXCLUSIVE)
                 ? TRUE
                 : funlock(env->me_lazy_fd, LCK_BODY);
    LeaveCriticalSection(&env->me_windowsbug_lock);
    if (!rc)
      mdbx_panic("%s failed: err %u", __func__, GetLastError());
  }
  
  /*----------------------------------------------------------------------------*/
  /* global `read` lock for readers registration,
   * exclusive locking `mti_numreaders` (second) cacheline */
  
  #define LCK_LO_OFFSET 0
  #define LCK_LO_LEN offsetof(MDBX_lockinfo, mti_numreaders)
  #define LCK_UP_OFFSET LCK_LO_LEN
  #define LCK_UP_LEN (sizeof(MDBX_lockinfo) - LCK_UP_OFFSET)
  #define LCK_LOWER LCK_LO_OFFSET, LCK_LO_LEN
  #define LCK_UPPER LCK_UP_OFFSET, LCK_UP_LEN
  
  MDBX_INTERNAL_FUNC int mdbx_rdt_lock(MDBX_env *env) {
    mdbx_srwlock_AcquireShared(&env->me_remap_guard);
    if (env->me_lfd == INVALID_HANDLE_VALUE)
      return MDBX_SUCCESS; /* readonly database in readonly filesystem */
  
    /* transition from S-? (used) to S-E (locked),
     * e.g. exclusive lock upper-part */
    if ((env->me_flags & MDBX_EXCLUSIVE) ||
        flock(env->me_lfd, LCK_EXCLUSIVE | LCK_WAITFOR, LCK_UPPER))
      return MDBX_SUCCESS;
  
    int rc = GetLastError();
    mdbx_srwlock_ReleaseShared(&env->me_remap_guard);
    return rc;
  }
  
  MDBX_INTERNAL_FUNC void mdbx_rdt_unlock(MDBX_env *env) {
    if (env->me_lfd != INVALID_HANDLE_VALUE) {
      /* transition from S-E (locked) to S-? (used), e.g. unlock upper-part */
      if ((env->me_flags & MDBX_EXCLUSIVE) == 0 &&
          !funlock(env->me_lfd, LCK_UPPER))
        mdbx_panic("%s failed: err %u", __func__, GetLastError());
    }
    mdbx_srwlock_ReleaseShared(&env->me_remap_guard);
  }
  
  MDBX_INTERNAL_FUNC int mdbx_lockfile(mdbx_filehandle_t fd, bool wait) {
    return flock(fd,
                 wait ? LCK_EXCLUSIVE | LCK_WAITFOR
                      : LCK_EXCLUSIVE | LCK_DONTWAIT,
                 0, LCK_MAXLEN)
               ? MDBX_SUCCESS
               : GetLastError();
  }
  
  static int suspend_and_append(mdbx_handle_array_t **array,
                                const DWORD ThreadId) {
    const unsigned limit = (*array)->limit;
    if ((*array)->count == limit) {
      void *ptr = mdbx_realloc(
          (limit > ARRAY_LENGTH((*array)->handles))
              ? *array
              : /* don't free initial array on the stack */ NULL,
          sizeof(mdbx_handle_array_t) +
              sizeof(HANDLE) * (limit * 2 - ARRAY_LENGTH((*array)->handles)));
      if (!ptr)
        return MDBX_ENOMEM;
      if (limit == ARRAY_LENGTH((*array)->handles))
        memcpy(ptr, *array, sizeof(mdbx_handle_array_t));
      *array = (mdbx_handle_array_t *)ptr;
      (*array)->limit = limit * 2;
    }
  
    HANDLE hThread = OpenThread(THREAD_SUSPEND_RESUME | THREAD_QUERY_INFORMATION,
                                FALSE, ThreadId);
    if (hThread == NULL)
      return GetLastError();
  
    if (SuspendThread(hThread) == -1) {
      int err = GetLastError();
      DWORD ExitCode;
      if (err == /* workaround for Win10 UCRT bug */ ERROR_ACCESS_DENIED ||
          !GetExitCodeThread(hThread, &ExitCode) || ExitCode != STILL_ACTIVE)
        err = MDBX_SUCCESS;
      CloseHandle(hThread);
      return err;
    }
  
    (*array)->handles[(*array)->count++] = hThread;
    return MDBX_SUCCESS;
  }
  
  MDBX_INTERNAL_FUNC int
  mdbx_suspend_threads_before_remap(MDBX_env *env, mdbx_handle_array_t **array) {
    const uintptr_t CurrentTid = GetCurrentThreadId();
    int rc;
    if (env->me_lck) {
      /* Scan LCK for threads of the current process */
      const MDBX_reader *const begin = env->me_lck->mti_readers;
      const MDBX_reader *const end = begin + env->me_lck->mti_numreaders;
      const uintptr_t WriteTxnOwner = env->me_txn0 ? env->me_txn0->mt_owner : 0;
      for (const MDBX_reader *reader = begin; reader < end; ++reader) {
        if (reader->mr_pid != env->me_pid || !reader->mr_tid) {
        skip_lck:
          continue;
        }
        if (reader->mr_tid == CurrentTid || reader->mr_tid == WriteTxnOwner)
          goto skip_lck;
        if (env->me_flags & MDBX_NOTLS) {
          /* Skip duplicates in no-tls mode */
          for (const MDBX_reader *scan = reader; --scan >= begin;)
            if (scan->mr_tid == reader->mr_tid)
              goto skip_lck;
        }
  
        rc = suspend_and_append(array, (mdbx_tid_t)reader->mr_tid);
        if (rc != MDBX_SUCCESS) {
        bailout_lck:
          (void)mdbx_resume_threads_after_remap(*array);
          return rc;
        }
      }
      if (WriteTxnOwner && WriteTxnOwner != CurrentTid) {
        rc = suspend_and_append(array, (mdbx_tid_t)WriteTxnOwner);
        if (rc != MDBX_SUCCESS)
          goto bailout_lck;
      }
    } else {
      /* Without LCK (i.e. read-only mode).
       * Walk through a snapshot of all running threads */
      mdbx_assert(env,
                  env->me_txn0 == NULL || (env->me_flags & MDBX_EXCLUSIVE) != 0);
      const HANDLE hSnapshot = CreateToolhelp32Snapshot(TH32CS_SNAPTHREAD, 0);
      if (hSnapshot == INVALID_HANDLE_VALUE)
        return GetLastError();
  
      THREADENTRY32 entry;
      entry.dwSize = sizeof(THREADENTRY32);
  
      if (!Thread32First(hSnapshot, &entry)) {
        rc = GetLastError();
      bailout_toolhelp:
        CloseHandle(hSnapshot);
        (void)mdbx_resume_threads_after_remap(*array);
        return rc;
      }
  
      do {
        if (entry.th32OwnerProcessID != env->me_pid ||
            entry.th32ThreadID == CurrentTid)
          continue;
  
        rc = suspend_and_append(array, entry.th32ThreadID);
        if (rc != MDBX_SUCCESS)
          goto bailout_toolhelp;
  
      } while (Thread32Next(hSnapshot, &entry));
  
      rc = GetLastError();
      if (rc != ERROR_NO_MORE_FILES)
        goto bailout_toolhelp;
      CloseHandle(hSnapshot);
    }
  
    return MDBX_SUCCESS;
  }
  
  MDBX_INTERNAL_FUNC int
  mdbx_resume_threads_after_remap(mdbx_handle_array_t *array) {
    int rc = MDBX_SUCCESS;
    for (unsigned i = 0; i < array->count; ++i) {
      const HANDLE hThread = array->handles[i];
      if (ResumeThread(hThread) == -1) {
        const int err = GetLastError();
        DWORD ExitCode;
        if (err != /* workaround for Win10 UCRT bug */ ERROR_ACCESS_DENIED &&
            GetExitCodeThread(hThread, &ExitCode) && ExitCode == STILL_ACTIVE)
          rc = err;
      }
      CloseHandle(hThread);
    }
    return rc;
  }
  
  /*----------------------------------------------------------------------------*/
  /* global `initial` lock for lockfile initialization,
   * exclusive/shared locking first cacheline */
  
  /* Briefly description of locking schema/algorithm:
   *  - Windows does not support upgrading or downgrading for file locking.
   *  - Therefore upgrading/downgrading is emulated by shared and exclusive
   *    locking of upper and lower halves.
   *  - In other words, we have FSM with possible 9 states,
   *    i.e. free/shared/exclusive x free/shared/exclusive == 9.
   *    Only 6 states of FSM are used, which 2 of ones are transitive.
   *
   * States:
   *   ?-?  = free, i.e. unlocked
   *   S-?  = used, i.e. shared lock
   *   E-?  = exclusive-read, i.e. operational exclusive
   *   ?-S
   *   ?-E  = middle (transitive state)
   *   S-S
   *   S-E  = locked (transitive state)
   *   E-S
   *   E-E  = exclusive-write, i.e. exclusive due (re)initialization
   *
   *  The mdbx_lck_seize() moves the locking-FSM from the initial free/unlocked
   *  state to the "exclusive write" (and returns MDBX_RESULT_TRUE) if possible,
   *  or to the "used" (and returns MDBX_RESULT_FALSE).
   *
   *  The mdbx_lck_downgrade() moves the locking-FSM from "exclusive write"
   *  state to the "used" (i.e. shared) state.
   *
   *  The mdbx_lck_upgrade() moves the locking-FSM from "used" (i.e. shared)
   *  state to the "exclusive write" state.
   */
  
  static void lck_unlock(MDBX_env *env) {
    int err;
  
    if (env->me_lfd != INVALID_HANDLE_VALUE) {
      /* double `unlock` for robustly remove overlapped shared/exclusive locks */
      while (funlock(env->me_lfd, LCK_LOWER))
        ;
      err = GetLastError();
      assert(err == ERROR_NOT_LOCKED ||
             (mdbx_RunningUnderWine() && err == ERROR_LOCK_VIOLATION));
      (void)err;
      SetLastError(ERROR_SUCCESS);
  
      while (funlock(env->me_lfd, LCK_UPPER))
        ;
      err = GetLastError();
      assert(err == ERROR_NOT_LOCKED ||
             (mdbx_RunningUnderWine() && err == ERROR_LOCK_VIOLATION));
      (void)err;
      SetLastError(ERROR_SUCCESS);
    }
  
    if (env->me_lazy_fd != INVALID_HANDLE_VALUE) {
      /* explicitly unlock to avoid latency for other processes (windows kernel
       * releases such locks via deferred queues) */
      while (funlock(env->me_lazy_fd, LCK_BODY))
        ;
      err = GetLastError();
      assert(err == ERROR_NOT_LOCKED ||
             (mdbx_RunningUnderWine() && err == ERROR_LOCK_VIOLATION));
      (void)err;
      SetLastError(ERROR_SUCCESS);
  
      while (funlock(env->me_lazy_fd, LCK_WHOLE))
        ;
      err = GetLastError();
      assert(err == ERROR_NOT_LOCKED ||
             (mdbx_RunningUnderWine() && err == ERROR_LOCK_VIOLATION));
      (void)err;
      SetLastError(ERROR_SUCCESS);
    }
  }
  
  /* Seize state as 'exclusive-write' (E-E and returns MDBX_RESULT_TRUE)
   * or as 'used' (S-? and returns MDBX_RESULT_FALSE).
   * Otherwise returns an error. */
  static int internal_seize_lck(HANDLE lfd) {
    int rc;
    assert(lfd != INVALID_HANDLE_VALUE);
  
    /* 1) now on ?-? (free), get ?-E (middle) */
    mdbx_jitter4testing(false);
    if (!flock(lfd, LCK_EXCLUSIVE | LCK_WAITFOR, LCK_UPPER)) {
      rc = GetLastError() /* 2) something went wrong, give up */;
      mdbx_error("%s, err %u", "?-?(free) >> ?-E(middle)", rc);
      return rc;
    }
  
    /* 3) now on ?-E (middle), try E-E (exclusive-write) */
    mdbx_jitter4testing(false);
    if (flock(lfd, LCK_EXCLUSIVE | LCK_DONTWAIT, LCK_LOWER))
      return MDBX_RESULT_TRUE /* 4) got E-E (exclusive-write), done */;
  
    /* 5) still on ?-E (middle) */
    rc = GetLastError();
    mdbx_jitter4testing(false);
    if (rc != ERROR_SHARING_VIOLATION && rc != ERROR_LOCK_VIOLATION) {
      /* 6) something went wrong, give up */
      if (!funlock(lfd, LCK_UPPER))
        mdbx_panic("%s(%s) failed: err %u", __func__, "?-E(middle) >> ?-?(free)",
                   GetLastError());
      return rc;
    }
  
    /* 7) still on ?-E (middle), try S-E (locked) */
    mdbx_jitter4testing(false);
    rc = flock(lfd, LCK_SHARED | LCK_DONTWAIT, LCK_LOWER) ? MDBX_RESULT_FALSE
                                                          : GetLastError();
  
    mdbx_jitter4testing(false);
    if (rc != MDBX_RESULT_FALSE)
      mdbx_error("%s, err %u", "?-E(middle) >> S-E(locked)", rc);
  
    /* 8) now on S-E (locked) or still on ?-E (middle),
     *    transition to S-? (used) or ?-? (free) */
    if (!funlock(lfd, LCK_UPPER))
      mdbx_panic("%s(%s) failed: err %u", __func__,
                 "X-E(locked/middle) >> X-?(used/free)", GetLastError());
  
    /* 9) now on S-? (used, DONE) or ?-? (free, FAILURE) */
    return rc;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_lck_seize(MDBX_env *env) {
    int rc;
  
    assert(env->me_lazy_fd != INVALID_HANDLE_VALUE);
    if (env->me_flags & MDBX_EXCLUSIVE)
      return MDBX_RESULT_TRUE /* nope since files were must be opened
                                 non-shareable */
          ;
  
    if (env->me_lfd == INVALID_HANDLE_VALUE) {
      /* LY: without-lck mode (e.g. on read-only filesystem) */
      mdbx_jitter4testing(false);
      if (!flock(env->me_lazy_fd, LCK_SHARED | LCK_DONTWAIT, LCK_WHOLE)) {
        rc = GetLastError();
        mdbx_error("%s, err %u", "without-lck", rc);
        return rc;
      }
      return MDBX_RESULT_FALSE;
    }
  
    rc = internal_seize_lck(env->me_lfd);
    mdbx_jitter4testing(false);
    if (rc == MDBX_RESULT_TRUE && (env->me_flags & MDBX_RDONLY) == 0) {
      /* Check that another process don't operates in without-lck mode.
       * Doing such check by exclusive locking the body-part of db. Should be
       * noted:
       *  - we need an exclusive lock for do so;
       *  - we can't lock meta-pages, otherwise other process could get an error
       *    while opening db in valid (non-conflict) mode. */
      if (!flock(env->me_lazy_fd, LCK_EXCLUSIVE | LCK_DONTWAIT, LCK_BODY)) {
        rc = GetLastError();
        mdbx_error("%s, err %u", "lock-against-without-lck", rc);
        mdbx_jitter4testing(false);
        lck_unlock(env);
      } else {
        mdbx_jitter4testing(false);
        if (!funlock(env->me_lazy_fd, LCK_BODY))
          mdbx_panic("%s(%s) failed: err %u", __func__,
                     "unlock-against-without-lck", GetLastError());
      }
    }
  
    return rc;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_lck_downgrade(MDBX_env *env) {
    /* Transite from exclusive-write state (E-E) to used (S-?) */
    assert(env->me_lazy_fd != INVALID_HANDLE_VALUE);
    assert(env->me_lfd != INVALID_HANDLE_VALUE);
  
    if (env->me_flags & MDBX_EXCLUSIVE)
      return MDBX_SUCCESS /* nope since files were must be opened non-shareable */
          ;
    /* 1) now at E-E (exclusive-write), transition to ?_E (middle) */
    if (!funlock(env->me_lfd, LCK_LOWER))
      mdbx_panic("%s(%s) failed: err %u", __func__,
                 "E-E(exclusive-write) >> ?-E(middle)", GetLastError());
  
    /* 2) now at ?-E (middle), transition to S-E (locked) */
    if (!flock(env->me_lfd, LCK_SHARED | LCK_DONTWAIT, LCK_LOWER)) {
      int rc = GetLastError() /* 3) something went wrong, give up */;
      mdbx_error("%s, err %u", "?-E(middle) >> S-E(locked)", rc);
      return rc;
    }
  
    /* 4) got S-E (locked), continue transition to S-? (used) */
    if (!funlock(env->me_lfd, LCK_UPPER))
      mdbx_panic("%s(%s) failed: err %u", __func__, "S-E(locked) >> S-?(used)",
                 GetLastError());
  
    return MDBX_SUCCESS /* 5) now at S-? (used), done */;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_lck_upgrade(MDBX_env *env) {
    /* Transite from used state (S-?) to exclusive-write (E-E) */
    assert(env->me_lfd != INVALID_HANDLE_VALUE);
  
    if (env->me_flags & MDBX_EXCLUSIVE)
      return MDBX_SUCCESS /* nope since files were must be opened non-shareable */
          ;
  
    int rc;
    /* 1) now on S-? (used), try S-E (locked) */
    mdbx_jitter4testing(false);
    if (!flock(env->me_lfd, LCK_EXCLUSIVE | LCK_DONTWAIT, LCK_UPPER)) {
      rc = GetLastError() /* 2) something went wrong, give up */;
      mdbx_verbose("%s, err %u", "S-?(used) >> S-E(locked)", rc);
      return rc;
    }
  
    /* 3) now on S-E (locked), transition to ?-E (middle) */
    if (!funlock(env->me_lfd, LCK_LOWER))
      mdbx_panic("%s(%s) failed: err %u", __func__, "S-E(locked) >> ?-E(middle)",
                 GetLastError());
  
    /* 4) now on ?-E (middle), try E-E (exclusive-write) */
    mdbx_jitter4testing(false);
    if (!flock(env->me_lfd, LCK_EXCLUSIVE | LCK_DONTWAIT, LCK_LOWER)) {
      rc = GetLastError() /* 5) something went wrong, give up */;
      mdbx_verbose("%s, err %u", "?-E(middle) >> E-E(exclusive-write)", rc);
      return rc;
    }
  
    return MDBX_SUCCESS /* 6) now at E-E (exclusive-write), done */;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_lck_init(MDBX_env *env,
                                       MDBX_env *inprocess_neighbor,
                                       int global_uniqueness_flag) {
    (void)env;
    (void)inprocess_neighbor;
    (void)global_uniqueness_flag;
    return MDBX_SUCCESS;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_lck_destroy(MDBX_env *env,
                                          MDBX_env *inprocess_neighbor) {
    /* LY: should unmap before releasing the locks to avoid race condition and
     * STATUS_USER_MAPPED_FILE/ERROR_USER_MAPPED_FILE */
    if (env->me_map)
      mdbx_munmap(&env->me_dxb_mmap);
    if (env->me_lck) {
      const bool synced = env->me_lck_mmap.lck->mti_unsynced_pages == 0;
      mdbx_munmap(&env->me_lck_mmap);
      if (synced && !inprocess_neighbor && env->me_lfd != INVALID_HANDLE_VALUE &&
          mdbx_lck_upgrade(env) == MDBX_SUCCESS)
        /* this will fail if LCK is used/mmapped by other process(es) */
        mdbx_ftruncate(env->me_lfd, 0);
    }
    lck_unlock(env);
    return MDBX_SUCCESS;
  }
  
  /*----------------------------------------------------------------------------*/
  /* reader checking (by pid) */
  
  MDBX_INTERNAL_FUNC int mdbx_rpid_set(MDBX_env *env) {
    (void)env;
    return MDBX_SUCCESS;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_rpid_clear(MDBX_env *env) {
    (void)env;
    return MDBX_SUCCESS;
  }
  
  /* Checks reader by pid.
   *
   * Returns:
   *   MDBX_RESULT_TRUE, if pid is live (unable to acquire lock)
   *   MDBX_RESULT_FALSE, if pid is dead (lock acquired)
   *   or otherwise the errcode. */
  MDBX_INTERNAL_FUNC int mdbx_rpid_check(MDBX_env *env, uint32_t pid) {
    (void)env;
    HANDLE hProcess = OpenProcess(SYNCHRONIZE, FALSE, pid);
    int rc;
    if (likely(hProcess)) {
      rc = WaitForSingleObject(hProcess, 0);
      if (unlikely(rc == WAIT_FAILED))
        rc = GetLastError();
      CloseHandle(hProcess);
    } else {
      rc = GetLastError();
    }
  
    switch (rc) {
    case ERROR_INVALID_PARAMETER:
      /* pid seems invalid */
      return MDBX_RESULT_FALSE;
    case WAIT_OBJECT_0:
      /* process just exited */
      return MDBX_RESULT_FALSE;
    case ERROR_ACCESS_DENIED:
      /* The ERROR_ACCESS_DENIED would be returned for CSRSS-processes, etc.
       * assume pid exists */
      return MDBX_RESULT_TRUE;
    case WAIT_TIMEOUT:
      /* pid running */
      return MDBX_RESULT_TRUE;
    default:
      /* failure */
      return rc;
    }
  }
  
  //----------------------------------------------------------------------------
  // Stub for slim read-write lock
  // Copyright (C) 1995-2002 Brad Wilson
  
  static void WINAPI stub_srwlock_Init(MDBX_srwlock *srwl) {
    srwl->readerCount = srwl->writerCount = 0;
  }
  
  static void WINAPI stub_srwlock_AcquireShared(MDBX_srwlock *srwl) {
    while (true) {
      assert(srwl->writerCount >= 0 && srwl->readerCount >= 0);
  
      //  If there's a writer already, spin without unnecessarily
      //  interlocking the CPUs
      if (srwl->writerCount != 0) {
        YieldProcessor();
        continue;
      }
  
      //  Add to the readers list
      _InterlockedIncrement(&srwl->readerCount);
  
      // Check for writers again (we may have been preempted). If
      // there are no writers writing or waiting, then we're done.
      if (srwl->writerCount == 0)
        break;
  
      // Remove from the readers list, spin, try again
      _InterlockedDecrement(&srwl->readerCount);
      YieldProcessor();
    }
  }
  
  static void WINAPI stub_srwlock_ReleaseShared(MDBX_srwlock *srwl) {
    assert(srwl->readerCount > 0);
    _InterlockedDecrement(&srwl->readerCount);
  }
  
  static void WINAPI stub_srwlock_AcquireExclusive(MDBX_srwlock *srwl) {
    while (true) {
      assert(srwl->writerCount >= 0 && srwl->readerCount >= 0);
  
      //  If there's a writer already, spin without unnecessarily
      //  interlocking the CPUs
      if (srwl->writerCount != 0) {
        YieldProcessor();
        continue;
      }
  
      // See if we can become the writer (expensive, because it inter-
      // locks the CPUs, so writing should be an infrequent process)
      if (_InterlockedExchange(&srwl->writerCount, 1) == 0)
        break;
    }
  
    // Now we're the writer, but there may be outstanding readers.
    // Spin until there aren't any more; new readers will wait now
    // that we're the writer.
    while (srwl->readerCount != 0) {
      assert(srwl->writerCount >= 0 && srwl->readerCount >= 0);
      YieldProcessor();
    }
  }
  
  static void WINAPI stub_srwlock_ReleaseExclusive(MDBX_srwlock *srwl) {
    assert(srwl->writerCount == 1 && srwl->readerCount >= 0);
    srwl->writerCount = 0;
  }
  
  MDBX_srwlock_function mdbx_srwlock_Init, mdbx_srwlock_AcquireShared,
      mdbx_srwlock_ReleaseShared, mdbx_srwlock_AcquireExclusive,
      mdbx_srwlock_ReleaseExclusive;
  
  /*----------------------------------------------------------------------------*/
  
  #if 0  /* LY: unused for now */
  static DWORD WINAPI stub_DiscardVirtualMemory(PVOID VirtualAddress,
                                                SIZE_T Size) {
    return VirtualAlloc(VirtualAddress, Size, MEM_RESET, PAGE_NOACCESS)
               ? ERROR_SUCCESS
  	  : GetLastError();
  }
  #endif /* unused for now */
  
  static uint64_t WINAPI stub_GetTickCount64(void) {
    LARGE_INTEGER Counter, Frequency;
    return (QueryPerformanceFrequency(&Frequency) &&
            QueryPerformanceCounter(&Counter))
               ? Counter.QuadPart * 1000ul / Frequency.QuadPart
               : 0;
  }
  
  /*----------------------------------------------------------------------------*/
  #ifndef MDBX_ALLOY
  MDBX_NtExtendSection mdbx_NtExtendSection;
  MDBX_GetFileInformationByHandleEx mdbx_GetFileInformationByHandleEx;
  MDBX_GetVolumeInformationByHandleW mdbx_GetVolumeInformationByHandleW;
  MDBX_GetFinalPathNameByHandleW mdbx_GetFinalPathNameByHandleW;
  MDBX_SetFileInformationByHandle mdbx_SetFileInformationByHandle;
  MDBX_NtFsControlFile mdbx_NtFsControlFile;
  MDBX_PrefetchVirtualMemory mdbx_PrefetchVirtualMemory;
  MDBX_GetTickCount64 mdbx_GetTickCount64;
  MDBX_RegGetValueA mdbx_RegGetValueA;
  #if 0  /* LY: unused for now */
  MDBX_DiscardVirtualMemory mdbx_DiscardVirtualMemory;
  MDBX_OfferVirtualMemory mdbx_OfferVirtualMemory;
  MDBX_ReclaimVirtualMemory mdbx_ReclaimVirtualMemory;
  #endif /* unused for now */
  #endif /* MDBX_ALLOY */
  
  static void mdbx_winnt_import(void) {
    const HINSTANCE hNtdll = GetModuleHandleA("ntdll.dll");
  
  #define GET_PROC_ADDR(dll, ENTRY)                                              \
    mdbx_##ENTRY = (MDBX_##ENTRY)GetProcAddress(dll, #ENTRY)
  
    if (GetProcAddress(hNtdll, "wine_get_version")) {
      assert(mdbx_RunningUnderWine());
    } else {
      GET_PROC_ADDR(hNtdll, NtFsControlFile);
      GET_PROC_ADDR(hNtdll, NtExtendSection);
      assert(!mdbx_RunningUnderWine());
    }
  
    const HINSTANCE hKernel32dll = GetModuleHandleA("kernel32.dll");
    GET_PROC_ADDR(hKernel32dll, GetFileInformationByHandleEx);
    GET_PROC_ADDR(hKernel32dll, GetTickCount64);
    if (!mdbx_GetTickCount64)
      mdbx_GetTickCount64 = stub_GetTickCount64;
    if (!mdbx_RunningUnderWine()) {
      GET_PROC_ADDR(hKernel32dll, SetFileInformationByHandle);
      GET_PROC_ADDR(hKernel32dll, GetVolumeInformationByHandleW);
      GET_PROC_ADDR(hKernel32dll, GetFinalPathNameByHandleW);
      GET_PROC_ADDR(hKernel32dll, PrefetchVirtualMemory);
    }
  
    const HINSTANCE hAdvapi32dll = GetModuleHandleA("advapi32.dll");
    GET_PROC_ADDR(hAdvapi32dll, RegGetValueA);
  
  #if 0  /* LY: unused for now */
    if (!mdbx_RunningUnderWine()) {
      GET_PROC_ADDR(hKernel32dll, DiscardVirtualMemory);
      GET_PROC_ADDR(hKernel32dll, OfferVirtualMemory);
      GET_PROC_ADDR(hKernel32dll, ReclaimVirtualMemory);
    }
    if (!mdbx_DiscardVirtualMemory)
      mdbx_DiscardVirtualMemory = stub_DiscardVirtualMemory;
    if (!mdbx_OfferVirtualMemory)
      mdbx_OfferVirtualMemory = stub_OfferVirtualMemory;
    if (!mdbx_ReclaimVirtualMemory)
      mdbx_ReclaimVirtualMemory = stub_ReclaimVirtualMemory;
  #endif /* unused for now */
  
  #undef GET_PROC_ADDR
  
    const MDBX_srwlock_function init =
        (MDBX_srwlock_function)GetProcAddress(hKernel32dll, "InitializeSRWLock");
    if (init != NULL) {
      mdbx_srwlock_Init = init;
      mdbx_srwlock_AcquireShared = (MDBX_srwlock_function)GetProcAddress(
          hKernel32dll, "AcquireSRWLockShared");
      mdbx_srwlock_ReleaseShared = (MDBX_srwlock_function)GetProcAddress(
          hKernel32dll, "ReleaseSRWLockShared");
      mdbx_srwlock_AcquireExclusive = (MDBX_srwlock_function)GetProcAddress(
          hKernel32dll, "AcquireSRWLockExclusive");
      mdbx_srwlock_ReleaseExclusive = (MDBX_srwlock_function)GetProcAddress(
          hKernel32dll, "ReleaseSRWLockExclusive");
    } else {
      mdbx_srwlock_Init = stub_srwlock_Init;
      mdbx_srwlock_AcquireShared = stub_srwlock_AcquireShared;
      mdbx_srwlock_ReleaseShared = stub_srwlock_ReleaseShared;
      mdbx_srwlock_AcquireExclusive = stub_srwlock_AcquireExclusive;
      mdbx_srwlock_ReleaseExclusive = stub_srwlock_ReleaseExclusive;
    }
  }
  
  #endif /* Windows LCK-implementation */
  /*
   * Copyright 2015-2020 Leonid Yuriev <leo@yuriev.ru>
   * and other libmdbx authors: please see AUTHORS file.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted only as authorized by the OpenLDAP
   * Public License.
   *
   * A copy of this license is available in the file LICENSE in the
   * top-level directory of the distribution or, alternatively, at
   * <http://www.OpenLDAP.org/license.html>.
   */
  
  #if !(defined(_WIN32) || defined(_WIN64)) /* !Windows LCK-implementation */
  
  #include <sys/sem.h>
  
  /*----------------------------------------------------------------------------*/
  /* global constructor/destructor */
  
  #if defined(__linux__) || defined(__gnu_linux__)
  
  #include <sys/utsname.h>
  
  #ifndef MDBX_ALLOY
  uint32_t mdbx_linux_kernel_version;
  bool mdbx_RunningOnWSL1;
  #endif /* MDBX_ALLOY */
  
  static __cold uint8_t probe_for_WSL(const char *tag) {
    const char *const WSL = strstr(tag, "WSL");
    if (WSL && WSL[3] >= '2' && WSL[3] <= '9')
      return WSL[3] - '0';
    const char *const wsl = strstr(tag, "wsl");
    if (wsl && wsl[3] >= '2' && wsl[3] <= '9')
      return wsl[3] - '0';
    return (WSL || wsl || strcasestr(tag, "Microsoft")) ? 1 : 0;
  }
  
  #endif /* Linux */
  
  static __cold __attribute__((__constructor__)) void
  mdbx_global_constructor(void) {
  #if defined(__linux__) || defined(__gnu_linux__)
    struct utsname buffer;
    if (uname(&buffer) == 0) {
      /* "Official" way of detecting WSL1 but not WSL2
       * https://github.com/Microsoft/WSL/issues/423#issuecomment-221627364
       *
       * WARNING: False negative detection of WSL1 will result in DATA LOSS!
       * So, the REQUIREMENTS for this code:
       *  1. MUST detect WSL1 without false-negatives.
       *  2. DESIRABLE detect WSL2 but without the risk of violating the first. */
      mdbx_RunningOnWSL1 = probe_for_WSL(buffer.version) == 1 ||
                           probe_for_WSL(buffer.sysname) == 1 ||
                           probe_for_WSL(buffer.release) == 1;
      int i = 0;
      char *p = buffer.release;
      while (*p && i < 4) {
        if (*p >= '0' && *p <= '9') {
          long number = strtol(p, &p, 10);
          if (number > 0) {
            if (number > 255)
              number = 255;
            mdbx_linux_kernel_version += number << (24 - i * 8);
          }
          ++i;
        } else {
          ++p;
        }
      }
    }
  #endif /* Linux */
  
    mdbx_rthc_global_init();
  }
  
  static __cold __attribute__((__destructor__)) void
  mdbx_global_destructor(void) {
    mdbx_rthc_global_dtor();
  }
  
  /*----------------------------------------------------------------------------*/
  /* lck */
  
  /* Описание реализации блокировок для POSIX & Linux:
   *
   * lck-файл отображается в память, в нём организуется таблица читателей и
   * размещаются совместно используемые posix-мьютексы (futex). Посредством
   * этих мьютексов (см struct MDBX_lockinfo) реализуются:
   *  - Блокировка таблицы читателей для регистрации,
   *    т.е. функции mdbx_rdt_lock() и mdbx_rdt_unlock().
   *  - Блокировка БД для пишущих транзакций,
   *    т.е. функции mdbx_txn_lock() и mdbx_txn_unlock().
   *
   * Остальной функционал реализуется отдельно посредством файловых блокировок:
   *  - Первоначальный захват БД в режиме exclusive/shared и последующий перевод
   *    в операционный режим, функции mdbx_lck_seize() и mdbx_lck_downgrade().
   *  - Проверка присутствие процессов-читателей,
   *    т.е. функции mdbx_rpid_set(), mdbx_rpid_clear() и mdbx_rpid_check().
   *
   * Для блокировки файлов используется fcntl(F_SETLK), так как:
   *  - lockf() оперирует только эксклюзивной блокировкой и требует
   *    открытия файла в RW-режиме.
   *  - flock() не гарантирует атомарности при смене блокировок
   *    и оперирует только всем файлом целиком.
   *  - Для контроля процессов-читателей используются однобайтовые
   *    range-блокировки lck-файла посредством fcntl(F_SETLK). При этом
   *    в качестве позиции используется pid процесса-читателя.
   *  - Для первоначального захвата и shared/exclusive выполняется блокировка
   *    основного файла БД и при успехе lck-файла.
   *
   * ----------------------------------------------------------------------------
   * УДЕРЖИВАЕМЫЕ БЛОКИРОВКИ В ЗАВИСИМОСТИ ОТ РЕЖИМА И СОСТОЯНИЯ
   *
   * Эксклюзивный режим без lck-файла:
   *   = заблокирован весь dxb-файл посредством F_RDLCK или F_WRLCK,
   *     в зависимости от MDBX_RDONLY.
   *
   * Не-операционный режим на время пере-инициализации и разрушении lck-файла:
   *   = F_WRLCK блокировка первого байта lck-файла, другие процессы ждут её
   *     снятия при получении F_RDLCK через F_SETLKW.
   *   - блокировки dxb-файла могут меняться до снятие эксклюзивной блокировки
   *    lck-файла:
   *       + для НЕ-эксклюзивного режима блокировка pid-байта в dxb-файле
   *         посредством F_RDLCK или F_WRLCK, в зависимости от MDBX_RDONLY.
   *       + для ЭКСКЛЮЗИВНОГО режима блокировка pid-байта всего dxb-файла
   *         посредством F_RDLCK или F_WRLCK, в зависимости от MDBX_RDONLY.
   *
   * ОПЕРАЦИОННЫЙ режим с lck-файлом:
   *   = F_RDLCK блокировка первого байта lck-файла, другие процессы не могут
   *     получить F_WRLCK и таким образом видят что БД используется.
   *   + F_WRLCK блокировка pid-байта в clk-файле после первой транзакции чтения.
   *   + для НЕ-эксклюзивного режима блокировка pid-байта в dxb-файле
   *     посредством F_RDLCK или F_WRLCK, в зависимости от MDBX_RDONLY.
   *   + для ЭКСКЛЮЗИВНОГО режима блокировка pid-байта всего dxb-файла
   *     посредством F_RDLCK или F_WRLCK, в зависимости от MDBX_RDONLY.
   */
  
  #if MDBX_USE_OFDLOCKS
  static int op_setlk, op_setlkw, op_getlk;
  static void __cold choice_fcntl() {
    assert(!op_setlk && !op_setlkw && !op_getlk);
    if ((mdbx_runtime_flags & MDBX_DBG_LEGACY_MULTIOPEN) == 0
  #if defined(__linux__) || defined(__gnu_linux__)
        && mdbx_linux_kernel_version >
               0x030f0000 /* OFD locks are available since 3.15, but engages here
                             only for 3.16 and later kernels (i.e. LTS) because
                             of reliability reasons */
  #endif                  /* linux */
    ) {
      op_setlk = F_OFD_SETLK;
      op_setlkw = F_OFD_SETLKW;
      op_getlk = F_OFD_GETLK;
      return;
    }
    op_setlk = F_SETLK;
    op_setlkw = F_SETLKW;
    op_getlk = F_GETLK;
  }
  #else
  #define op_setlk F_SETLK
  #define op_setlkw F_SETLKW
  #define op_getlk F_GETLK
  #endif /* MDBX_USE_OFDLOCKS */
  
  #ifndef OFF_T_MAX
  #define OFF_T_MAX                                                              \
    ((sizeof(off_t) > 4 ? INT64_MAX : INT32_MAX) & ~(size_t)0xffff)
  #endif
  
  static int lck_op(mdbx_filehandle_t fd, int cmd, int lck, off_t offset,
                    off_t len) {
    mdbx_jitter4testing(true);
    for (;;) {
      struct flock lock_op;
      memset(&lock_op, 0, sizeof(lock_op));
      lock_op.l_type = lck;
      lock_op.l_whence = SEEK_SET;
      lock_op.l_start = offset;
      lock_op.l_len = len;
      int rc = fcntl(fd, cmd, &lock_op);
      mdbx_jitter4testing(true);
      if (rc != -1) {
        if (cmd == op_getlk) {
          /* Checks reader by pid. Returns:
           *   MDBX_RESULT_TRUE   - if pid is live (reader holds a lock).
           *   MDBX_RESULT_FALSE  - if pid is dead (a lock could be placed). */
          return (lock_op.l_type == F_UNLCK) ? MDBX_RESULT_FALSE
                                             : MDBX_RESULT_TRUE;
        }
        return MDBX_SUCCESS;
      }
      rc = errno;
      if (rc != EINTR || cmd == op_setlkw) {
        mdbx_assert(nullptr, MDBX_IS_ERROR(rc));
        return rc;
      }
    }
  }
  
  MDBX_INTERNAL_FUNC int mdbx_lockfile(mdbx_filehandle_t fd, bool wait) {
  #if MDBX_USE_OFDLOCKS
    if (unlikely(op_setlk == 0))
      choice_fcntl();
  #endif /* MDBX_USE_OFDLOCKS */
    return lck_op(fd, wait ? op_setlkw : op_setlk, F_WRLCK, 0, OFF_T_MAX);
  }
  
  MDBX_INTERNAL_FUNC int mdbx_rpid_set(MDBX_env *env) {
    assert(env->me_lfd != INVALID_HANDLE_VALUE);
    assert(env->me_pid > 0);
    if (unlikely(mdbx_getpid() != env->me_pid))
      return MDBX_PANIC;
    return lck_op(env->me_lfd, op_setlk, F_WRLCK, env->me_pid, 1);
  }
  
  MDBX_INTERNAL_FUNC int mdbx_rpid_clear(MDBX_env *env) {
    assert(env->me_lfd != INVALID_HANDLE_VALUE);
    assert(env->me_pid > 0);
    return lck_op(env->me_lfd, op_setlk, F_UNLCK, env->me_pid, 1);
  }
  
  MDBX_INTERNAL_FUNC int mdbx_rpid_check(MDBX_env *env, uint32_t pid) {
    assert(env->me_lfd != INVALID_HANDLE_VALUE);
    assert(pid > 0);
    return lck_op(env->me_lfd, op_getlk, F_WRLCK, pid, 1);
  }
  
  /*---------------------------------------------------------------------------*/
  
  #if MDBX_LOCKING > MDBX_LOCKING_SYSV
  MDBX_INTERNAL_FUNC int mdbx_ipclock_stub(mdbx_ipclock_t *ipc) {
  #if MDBX_LOCKING == MDBX_LOCKING_POSIX1988
    return sem_init(ipc, false, 1) ? errno : 0;
  #elif MDBX_LOCKING == MDBX_LOCKING_POSIX2001 ||                                \
      MDBX_LOCKING == MDBX_LOCKING_POSIX2008
    return pthread_mutex_init(ipc, nullptr);
  #else
  #error "FIXME"
  #endif
  }
  
  MDBX_INTERNAL_FUNC int mdbx_ipclock_destroy(mdbx_ipclock_t *ipc) {
  #if MDBX_LOCKING == MDBX_LOCKING_POSIX1988
    return sem_destroy(ipc) ? errno : 0;
  #elif MDBX_LOCKING == MDBX_LOCKING_POSIX2001 ||                                \
      MDBX_LOCKING == MDBX_LOCKING_POSIX2008
    return pthread_mutex_destroy(ipc);
  #else
  #error "FIXME"
  #endif
  }
  #endif /* MDBX_LOCKING > MDBX_LOCKING_SYSV */
  
  static int check_fstat(MDBX_env *env) {
    struct stat st;
  
    int rc = MDBX_SUCCESS;
    if (fstat(env->me_lazy_fd, &st)) {
      rc = errno;
      mdbx_error("fstat(%s), err %d", "DXB", rc);
      return rc;
    }
  
    if (!S_ISREG(st.st_mode) || st.st_nlink < 1) {
  #ifdef EBADFD
      rc = EBADFD;
  #else
      rc = EPERM;
  #endif
      mdbx_error("%s %s, err %d", "DXB",
                 (st.st_nlink < 1) ? "file was removed" : "not a regular file",
                 rc);
      return rc;
    }
  
    if (st.st_size < (off_t)(MDBX_MIN_PAGESIZE * NUM_METAS)) {
      mdbx_verbose("dxb-file is too short (%u), exclusive-lock needed",
                   (unsigned)st.st_size);
      rc = MDBX_RESULT_TRUE;
    }
  
    //----------------------------------------------------------------------------
  
    if (fstat(env->me_lfd, &st)) {
      rc = errno;
      mdbx_error("fstat(%s), err %d", "LCK", rc);
      return rc;
    }
  
    if (!S_ISREG(st.st_mode) || st.st_nlink < 1) {
  #ifdef EBADFD
      rc = EBADFD;
  #else
      rc = EPERM;
  #endif
      mdbx_error("%s %s, err %d", "LCK",
                 (st.st_nlink < 1) ? "file was removed" : "not a regular file",
                 rc);
      return rc;
    }
  
    /* Checking file size for detect the situation when we got the shared lock
     * immediately after mdbx_lck_destroy(). */
    if (st.st_size < (off_t)(sizeof(MDBX_lockinfo) + sizeof(MDBX_reader))) {
      mdbx_verbose("lck-file is too short (%u), exclusive-lock needed",
                   (unsigned)st.st_size);
      rc = MDBX_RESULT_TRUE;
    }
  
    return rc;
  }
  
  MDBX_INTERNAL_FUNC int __cold mdbx_lck_seize(MDBX_env *env) {
    assert(env->me_lazy_fd != INVALID_HANDLE_VALUE);
    if (unlikely(mdbx_getpid() != env->me_pid))
      return MDBX_PANIC;
  #if MDBX_USE_OFDLOCKS
    if (unlikely(op_setlk == 0))
      choice_fcntl();
  #endif /* MDBX_USE_OFDLOCKS */
  
    int rc = MDBX_SUCCESS;
  #if defined(__linux__) || defined(__gnu_linux__)
    if (unlikely(mdbx_RunningOnWSL1)) {
      rc = ENOLCK /* No record locks available */;
      mdbx_error("%s, err %u",
                 "WSL1 (Windows Subsystem for Linux) is mad and trouble-full, "
                 "injecting failure to avoid data loss",
                 rc);
      return rc;
    }
  #endif /* Linux */
  
    if (env->me_lfd == INVALID_HANDLE_VALUE) {
      /* LY: without-lck mode (e.g. exclusive or on read-only filesystem) */
      rc =
          lck_op(env->me_lazy_fd, op_setlk,
                 (env->me_flags & MDBX_RDONLY) ? F_RDLCK : F_WRLCK, 0, OFF_T_MAX);
      if (rc != MDBX_SUCCESS) {
        mdbx_error("%s, err %u", "without-lck", rc);
        mdbx_assert(env, MDBX_IS_ERROR(rc));
        return rc;
      }
      return MDBX_RESULT_TRUE /* Done: return with exclusive locking. */;
    }
  #if defined(_POSIX_PRIORITY_SCHEDULING) && _POSIX_PRIORITY_SCHEDULING > 0
    sched_yield();
  #endif
  
  retry:
    if (rc == MDBX_RESULT_TRUE) {
      rc = lck_op(env->me_lfd, op_setlk, F_UNLCK, 0, 1);
      if (rc != MDBX_SUCCESS) {
        mdbx_error("%s, err %u", "unlock-before-retry", rc);
        mdbx_assert(env, MDBX_IS_ERROR(rc));
        return rc;
      }
    }
  
    /* Firstly try to get exclusive locking.  */
    rc = lck_op(env->me_lfd, op_setlk, F_WRLCK, 0, 1);
    if (rc == MDBX_SUCCESS) {
      rc = check_fstat(env);
      if (MDBX_IS_ERROR(rc))
        return rc;
  
    continue_dxb_exclusive:
      rc =
          lck_op(env->me_lazy_fd, op_setlk,
                 (env->me_flags & MDBX_RDONLY) ? F_RDLCK : F_WRLCK, 0, OFF_T_MAX);
      if (rc == MDBX_SUCCESS)
        return MDBX_RESULT_TRUE /* Done: return with exclusive locking. */;
  
      int err = check_fstat(env);
      if (MDBX_IS_ERROR(err))
        return err;
  
      /* the cause may be a collision with POSIX's file-lock recovery. */
      if (!(rc == EAGAIN || rc == EACCES || rc == EBUSY || rc == EWOULDBLOCK ||
            rc == EDEADLK)) {
        mdbx_error("%s, err %u", "dxb-exclusive", rc);
        mdbx_assert(env, MDBX_IS_ERROR(rc));
        return rc;
      }
  
      /* Fallback to lck-shared */
    } else if (!(rc == EAGAIN || rc == EACCES || rc == EBUSY ||
                 rc == EWOULDBLOCK || rc == EDEADLK)) {
      mdbx_error("%s, err %u", "try-exclusive", rc);
      mdbx_assert(env, MDBX_IS_ERROR(rc));
      return rc;
    }
  
    /* Here could be one of two:
     *  - mdbx_lck_destroy() from the another process was hold the lock
     *    during a destruction.
     *  - either mdbx_lck_seize() from the another process was got the exclusive
     *    lock and doing initialization.
     * For distinguish these cases will use size of the lck-file later. */
  
    /* Wait for lck-shared now. */
    /* Here may be await during transient processes, for instance until another
     * competing process doesn't call lck_downgrade(). */
    rc = lck_op(env->me_lfd, op_setlkw, F_RDLCK, 0, 1);
    if (rc != MDBX_SUCCESS) {
      mdbx_error("%s, err %u", "try-shared", rc);
      mdbx_assert(env, MDBX_IS_ERROR(rc));
      return rc;
    }
  
    rc = check_fstat(env);
    if (rc == MDBX_RESULT_TRUE)
      goto retry;
    if (rc != MDBX_SUCCESS) {
      mdbx_error("%s, err %u", "lck_fstat", rc);
      return rc;
    }
  
    /* got shared, retry exclusive */
    rc = lck_op(env->me_lfd, op_setlk, F_WRLCK, 0, 1);
    if (rc == MDBX_SUCCESS)
      goto continue_dxb_exclusive;
  
    if (!(rc == EAGAIN || rc == EACCES || rc == EBUSY || rc == EWOULDBLOCK ||
          rc == EDEADLK)) {
      mdbx_error("%s, err %u", "try-exclusive", rc);
      mdbx_assert(env, MDBX_IS_ERROR(rc));
      return rc;
    }
  
    /* Lock against another process operating in without-lck or exclusive mode. */
    rc =
        lck_op(env->me_lazy_fd, op_setlk,
               (env->me_flags & MDBX_RDONLY) ? F_RDLCK : F_WRLCK, env->me_pid, 1);
    if (rc != MDBX_SUCCESS) {
      mdbx_error("%s, err %u", "lock-against-without-lck", rc);
      mdbx_assert(env, MDBX_IS_ERROR(rc));
      return rc;
    }
  
    /* Done: return with shared locking. */
    return MDBX_RESULT_FALSE;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_lck_downgrade(MDBX_env *env) {
    assert(env->me_lfd != INVALID_HANDLE_VALUE);
    if (unlikely(mdbx_getpid() != env->me_pid))
      return MDBX_PANIC;
  
    int rc = MDBX_SUCCESS;
    if ((env->me_flags & MDBX_EXCLUSIVE) == 0) {
      rc = lck_op(env->me_lazy_fd, op_setlk, F_UNLCK, 0, env->me_pid);
      if (rc == MDBX_SUCCESS)
        rc = lck_op(env->me_lazy_fd, op_setlk, F_UNLCK, env->me_pid + 1,
                    OFF_T_MAX - env->me_pid - 1);
    }
    if (rc == MDBX_SUCCESS)
      rc = lck_op(env->me_lfd, op_setlk, F_RDLCK, 0, 1);
    if (unlikely(rc != 0)) {
      mdbx_error("%s, err %u", "lck", rc);
      assert(MDBX_IS_ERROR(rc));
    }
    return rc;
  }
  
  MDBX_INTERNAL_FUNC int __cold mdbx_lck_destroy(MDBX_env *env,
                                                 MDBX_env *inprocess_neighbor) {
    if (unlikely(mdbx_getpid() != env->me_pid))
      return MDBX_PANIC;
  
    int rc = MDBX_SUCCESS;
    struct stat lck_info;
    if (env->me_lfd != INVALID_HANDLE_VALUE && !inprocess_neighbor &&
        env->me_lck &&
        /* try get exclusive access */
        lck_op(env->me_lfd, op_setlk, F_WRLCK, 0, OFF_T_MAX) == 0 &&
        /* if LCK was not removed */
        fstat(env->me_lfd, &lck_info) == 0 && lck_info.st_nlink > 0 &&
        lck_op(env->me_lazy_fd, op_setlk,
               (env->me_flags & MDBX_RDONLY) ? F_RDLCK : F_WRLCK, 0,
               OFF_T_MAX) == 0) {
  
      mdbx_verbose("%p got exclusive, drown locks", (void *)env);
  #if MDBX_LOCKING == MDBX_LOCKING_SYSV
      if (env->me_sysv_ipc.semid != -1)
        rc = semctl(env->me_sysv_ipc.semid, 2, IPC_RMID) ? errno : 0;
  #else
      rc = mdbx_ipclock_destroy(&env->me_lck->mti_rlock);
      if (rc == 0)
        rc = mdbx_ipclock_destroy(&env->me_lck->mti_wlock);
  #endif /* MDBX_LOCKING */
  
      mdbx_assert(env, rc == 0);
      if (rc == 0) {
        const bool synced = env->me_lck_mmap.lck->mti_unsynced_pages == 0;
        mdbx_munmap(&env->me_lck_mmap);
        if (synced)
          rc = ftruncate(env->me_lfd, 0) ? errno : 0;
      }
  
      mdbx_jitter4testing(false);
    }
  
    /* 1) POSIX's fcntl() locks (i.e. when op_setlk == F_SETLK) should be restored
     * after file was closed.
     *
     * 2) File locks would be released (by kernel) while the file-descriptors will
     * be closed. But to avoid false-positive EACCESS and EDEADLK from the kernel,
     * locks should be released here explicitly with properly order. */
  
    /* close dxb and restore lock */
    if (env->me_dsync_fd != INVALID_HANDLE_VALUE) {
      if (unlikely(close(env->me_dsync_fd) != 0) && rc == MDBX_SUCCESS)
        rc = errno;
      env->me_dsync_fd = INVALID_HANDLE_VALUE;
    }
    if (env->me_lazy_fd != INVALID_HANDLE_VALUE) {
      if (unlikely(close(env->me_lazy_fd) != 0) && rc == MDBX_SUCCESS)
        rc = errno;
      env->me_lazy_fd = INVALID_HANDLE_VALUE;
      if (op_setlk == F_SETLK && inprocess_neighbor && rc == MDBX_SUCCESS) {
        /* restore file-lock */
        rc = lck_op(
            inprocess_neighbor->me_lazy_fd, F_SETLKW,
            (inprocess_neighbor->me_flags & MDBX_RDONLY) ? F_RDLCK : F_WRLCK,
            (inprocess_neighbor->me_flags & MDBX_EXCLUSIVE)
                ? 0
                : inprocess_neighbor->me_pid,
            (inprocess_neighbor->me_flags & MDBX_EXCLUSIVE) ? OFF_T_MAX : 1);
      }
    }
  
    /* close clk and restore locks */
    if (env->me_lfd != INVALID_HANDLE_VALUE) {
      if (unlikely(close(env->me_lfd) != 0) && rc == MDBX_SUCCESS)
        rc = errno;
      env->me_lfd = INVALID_HANDLE_VALUE;
      if (op_setlk == F_SETLK && inprocess_neighbor && rc == MDBX_SUCCESS) {
        /* restore file-locks */
        rc = lck_op(inprocess_neighbor->me_lfd, F_SETLKW, F_RDLCK, 0, 1);
        if (rc == MDBX_SUCCESS && inprocess_neighbor->me_live_reader)
          rc = mdbx_rpid_set(inprocess_neighbor);
      }
    }
  
    if (inprocess_neighbor && rc != MDBX_SUCCESS)
      inprocess_neighbor->me_flags |= MDBX_FATAL_ERROR;
    return rc;
  }
  
  /*---------------------------------------------------------------------------*/
  
  MDBX_INTERNAL_FUNC int __cold mdbx_lck_init(MDBX_env *env,
                                              MDBX_env *inprocess_neighbor,
                                              int global_uniqueness_flag) {
  #if MDBX_LOCKING == MDBX_LOCKING_SYSV
    int semid = -1;
    /* don't initialize semaphores twice */
    (void)inprocess_neighbor;
    if (global_uniqueness_flag == MDBX_RESULT_TRUE) {
      struct stat st;
      if (fstat(env->me_lazy_fd, &st))
        return errno;
    sysv_retry_create:
      semid = semget(env->me_sysv_ipc.key, 2,
                     IPC_CREAT | IPC_EXCL |
                         (st.st_mode & (S_IRWXU | S_IRWXG | S_IRWXO)));
      if (unlikely(semid == -1)) {
        int err = errno;
        if (err != EEXIST)
          return err;
  
        /* remove and re-create semaphore set */
        semid = semget(env->me_sysv_ipc.key, 2, 0);
        if (semid == -1) {
          err = errno;
          if (err != ENOENT)
            return err;
          goto sysv_retry_create;
        }
        if (semctl(semid, 2, IPC_RMID)) {
          err = errno;
          if (err != EIDRM)
            return err;
        }
        goto sysv_retry_create;
      }
  
      unsigned short val_array[2] = {1, 1};
      if (semctl(semid, 2, SETALL, val_array))
        return errno;
    } else {
      semid = semget(env->me_sysv_ipc.key, 2, 0);
      if (semid == -1)
        return errno;
  
      /* check read & write access */
      struct semid_ds data[2];
      if (semctl(semid, 2, IPC_STAT, data) || semctl(semid, 2, IPC_SET, data))
        return errno;
    }
  
    env->me_sysv_ipc.semid = semid;
    return MDBX_SUCCESS;
  
  #elif MDBX_LOCKING == MDBX_LOCKING_FUTEX
    (void)inprocess_neighbor;
    if (global_uniqueness_flag != MDBX_RESULT_TRUE)
      return MDBX_SUCCESS;
  #error "FIXME: Not implemented"
  #elif MDBX_LOCKING == MDBX_LOCKING_POSIX1988
  
    /* don't initialize semaphores twice */
    (void)inprocess_neighbor;
    if (global_uniqueness_flag == MDBX_RESULT_TRUE) {
      if (sem_init(&env->me_lck->mti_rlock, true, 1))
        return errno;
      if (sem_init(&env->me_lck->mti_wlock, true, 1))
        return errno;
    }
    return MDBX_SUCCESS;
  
  #elif MDBX_LOCKING == MDBX_LOCKING_POSIX2001 ||                                \
      MDBX_LOCKING == MDBX_LOCKING_POSIX2008
    if (inprocess_neighbor)
      return MDBX_SUCCESS /* don't need any initialization for mutexes
        if LCK already opened/used inside current process */
          ;
  
      /* FIXME: Unfortunately, there is no other reliable way but to long testing
       * on each platform. On the other hand, behavior like FreeBSD is incorrect
       * and we can expect it to be rare. Moreover, even on FreeBSD without
       * additional in-process initialization, the probability of an problem
       * occurring is vanishingly small, and the symptom is a return of EINVAL
       * while locking a mutex. In other words, in the worst case, the problem
       * results in an EINVAL error at the start of the transaction, but NOT data
       * loss, nor database corruption, nor other fatal troubles. Thus, the code
       * below I am inclined to think the workaround for erroneous platforms (like
       * FreeBSD), rather than a defect of libmdbx. */
  #if defined(__FreeBSD__)
    /* seems that shared mutexes on FreeBSD required in-process initialization */
    (void)global_uniqueness_flag;
  #else
    /* shared mutexes on many other platforms (including Darwin and Linux's
     * futexes) doesn't need any addition in-process initialization */
    if (global_uniqueness_flag != MDBX_RESULT_TRUE)
      return MDBX_SUCCESS;
  #endif
  
    pthread_mutexattr_t ma;
    int rc = pthread_mutexattr_init(&ma);
    if (rc)
      return rc;
  
    rc = pthread_mutexattr_setpshared(&ma, PTHREAD_PROCESS_SHARED);
    if (rc)
      goto bailout;
  
  #if MDBX_LOCKING == MDBX_LOCKING_POSIX2008
  #if defined(PTHREAD_MUTEX_ROBUST) || defined(pthread_mutexattr_setrobust)
    rc = pthread_mutexattr_setrobust(&ma, PTHREAD_MUTEX_ROBUST);
  #elif defined(PTHREAD_MUTEX_ROBUST_NP) ||                                      \
      defined(pthread_mutexattr_setrobust_np)
    rc = pthread_mutexattr_setrobust_np(&ma, PTHREAD_MUTEX_ROBUST_NP);
  #elif _POSIX_THREAD_PROCESS_SHARED < 200809L
    rc = pthread_mutexattr_setrobust_np(&ma, PTHREAD_MUTEX_ROBUST_NP);
  #else
    rc = pthread_mutexattr_setrobust(&ma, PTHREAD_MUTEX_ROBUST);
  #endif
    if (rc)
      goto bailout;
  #endif /* MDBX_LOCKING == MDBX_LOCKING_POSIX2008 */
  
  #if defined(_POSIX_THREAD_PRIO_INHERIT) && _POSIX_THREAD_PRIO_INHERIT >= 0 &&  \
      !defined(MDBX_SAFE4QEMU)
    rc = pthread_mutexattr_setprotocol(&ma, PTHREAD_PRIO_INHERIT);
    if (rc == ENOTSUP)
      rc = pthread_mutexattr_setprotocol(&ma, PTHREAD_PRIO_NONE);
    if (rc && rc != ENOTSUP)
      goto bailout;
  #endif /* PTHREAD_PRIO_INHERIT */
  
    rc = pthread_mutexattr_settype(&ma, PTHREAD_MUTEX_ERRORCHECK);
    if (rc && rc != ENOTSUP)
      goto bailout;
  
    rc = pthread_mutex_init(&env->me_lck->mti_rlock, &ma);
    if (rc)
      goto bailout;
    rc = pthread_mutex_init(&env->me_lck->mti_wlock, &ma);
  
  bailout:
    pthread_mutexattr_destroy(&ma);
    return rc;
  #else
  #error "FIXME"
  #endif /* MDBX_LOCKING > 0 */
  }
  
  static int __cold mdbx_ipclock_failed(MDBX_env *env, mdbx_ipclock_t *ipc,
                                        const int err) {
    int rc = err;
  #if MDBX_LOCKING == MDBX_LOCKING_POSIX2008 || MDBX_LOCKING == MDBX_LOCKING_SYSV
    if (err == EOWNERDEAD) {
      /* We own the mutex. Clean up after dead previous owner. */
  
      const bool rlocked = (env->me_lck && ipc == &env->me_lck->mti_rlock);
      rc = MDBX_SUCCESS;
      if (!rlocked) {
        if (unlikely(env->me_txn)) {
          /* env is hosed if the dead thread was ours */
          env->me_flags |= MDBX_FATAL_ERROR;
          env->me_txn = NULL;
          rc = MDBX_PANIC;
        }
      }
      mdbx_warning("%clock owner died, %s", (rlocked ? 'r' : 'w'),
                   (rc ? "this process' env is hosed" : "recovering"));
  
      int check_rc = mdbx_cleanup_dead_readers(env, rlocked, NULL);
      check_rc = (check_rc == MDBX_SUCCESS) ? MDBX_RESULT_TRUE : check_rc;
  
  #if MDBX_LOCKING == MDBX_LOCKING_SYSV
      rc = (rc == MDBX_SUCCESS) ? check_rc : rc;
  #else
  #if defined(PTHREAD_MUTEX_ROBUST) || defined(pthread_mutex_consistent)
      int mreco_rc = pthread_mutex_consistent(ipc);
  #elif defined(PTHREAD_MUTEX_ROBUST_NP) || defined(pthread_mutex_consistent_np)
      int mreco_rc = pthread_mutex_consistent_np(ipc);
  #elif _POSIX_THREAD_PROCESS_SHARED < 200809L
      int mreco_rc = pthread_mutex_consistent_np(ipc);
  #else
      int mreco_rc = pthread_mutex_consistent(ipc);
  #endif
      check_rc = (mreco_rc == 0) ? check_rc : mreco_rc;
  
      if (unlikely(mreco_rc))
        mdbx_error("lock recovery failed, %s", mdbx_strerror(mreco_rc));
  
      rc = (rc == MDBX_SUCCESS) ? check_rc : rc;
      if (MDBX_IS_ERROR(rc))
        pthread_mutex_unlock(ipc);
  #endif /* MDBX_LOCKING == MDBX_LOCKING_POSIX2008 */
      return rc;
    }
  #elif MDBX_LOCKING == MDBX_LOCKING_POSIX2001
    (void)ipc;
  #elif MDBX_LOCKING == MDBX_LOCKING_POSIX1988
    (void)ipc;
  #elif MDBX_LOCKING == MDBX_LOCKING_FUTEX
  #ifdef _MSC_VER
  #pragma message("warning: TODO")
  #else
  #warning "TODO"
  #endif
    (void)ipc;
  #else
  #error "FIXME"
  #endif /* MDBX_LOCKING */
  
    mdbx_error("mutex (un)lock failed, %s", mdbx_strerror(err));
    if (rc != EDEADLK)
      env->me_flags |= MDBX_FATAL_ERROR;
    return rc;
  }
  
  static int mdbx_ipclock_lock(MDBX_env *env, mdbx_ipclock_t *ipc,
                               const bool dont_wait) {
  #if MDBX_LOCKING == MDBX_LOCKING_POSIX2001 ||                                  \
      MDBX_LOCKING == MDBX_LOCKING_POSIX2008
    int rc = dont_wait ? pthread_mutex_trylock(ipc) : pthread_mutex_lock(ipc);
    rc = (rc == EBUSY && dont_wait) ? MDBX_BUSY : rc;
  #elif MDBX_LOCKING == MDBX_LOCKING_POSIX1988
    int rc = MDBX_SUCCESS;
    if (dont_wait) {
      if (sem_trywait(ipc)) {
        rc = errno;
        if (rc == EAGAIN)
          rc = MDBX_BUSY;
      }
    } else if (sem_wait(ipc))
      rc = errno;
  #elif MDBX_LOCKING == MDBX_LOCKING_SYSV
    struct sembuf op = {.sem_num = (ipc != env->me_wlock),
                        .sem_op = -1,
                        .sem_flg = dont_wait ? IPC_NOWAIT | SEM_UNDO : SEM_UNDO};
    int rc;
    if (semop(env->me_sysv_ipc.semid, &op, 1)) {
      rc = errno;
      if (dont_wait && rc == EAGAIN)
        rc = MDBX_BUSY;
    } else {
      rc = *ipc ? EOWNERDEAD : MDBX_SUCCESS;
      *ipc = env->me_pid;
    }
  #else
  #error "FIXME"
  #endif /* MDBX_LOCKING */
  
    if (unlikely(rc != MDBX_SUCCESS && rc != MDBX_BUSY))
      rc = mdbx_ipclock_failed(env, ipc, rc);
    return rc;
  }
  
  static int mdbx_ipclock_unlock(MDBX_env *env, mdbx_ipclock_t *ipc) {
  #if MDBX_LOCKING == MDBX_LOCKING_POSIX2001 ||                                  \
      MDBX_LOCKING == MDBX_LOCKING_POSIX2008
    int rc = pthread_mutex_unlock(ipc);
    (void)env;
  #elif MDBX_LOCKING == MDBX_LOCKING_POSIX1988
    int rc = sem_post(ipc) ? errno : MDBX_SUCCESS;
    (void)env;
  #elif MDBX_LOCKING == MDBX_LOCKING_SYSV
    if (unlikely(*ipc != (pid_t)env->me_pid))
      return EPERM;
    *ipc = 0;
    struct sembuf op = {
        .sem_num = (ipc != env->me_wlock), .sem_op = 1, .sem_flg = SEM_UNDO};
    int rc = semop(env->me_sysv_ipc.semid, &op, 1) ? errno : MDBX_SUCCESS;
  #else
  #error "FIXME"
  #endif /* MDBX_LOCKING */
    return rc;
  }
  
  MDBX_INTERNAL_FUNC int mdbx_rdt_lock(MDBX_env *env) {
    mdbx_trace("%s", ">>");
    mdbx_jitter4testing(true);
    int rc = mdbx_ipclock_lock(env, &env->me_lck->mti_rlock, false);
    mdbx_trace("<< rc %d", rc);
    return rc;
  }
  
  MDBX_INTERNAL_FUNC void mdbx_rdt_unlock(MDBX_env *env) {
    mdbx_trace("%s", ">>");
    int rc = mdbx_ipclock_unlock(env, &env->me_lck->mti_rlock);
    mdbx_trace("<< rc %d", rc);
    if (unlikely(rc != MDBX_SUCCESS))
      mdbx_panic("%s() failed: err %d\n", __func__, rc);
    mdbx_jitter4testing(true);
  }
  
  int mdbx_txn_lock(MDBX_env *env, bool dont_wait) {
    mdbx_trace("%swait %s", dont_wait ? "dont-" : "", ">>");
    mdbx_jitter4testing(true);
    int rc = mdbx_ipclock_lock(env, env->me_wlock, dont_wait);
    mdbx_trace("<< rc %d", rc);
    return MDBX_IS_ERROR(rc) ? rc : MDBX_SUCCESS;
  }
  
  void mdbx_txn_unlock(MDBX_env *env) {
    mdbx_trace("%s", ">>");
    int rc = mdbx_ipclock_unlock(env, env->me_wlock);
    mdbx_trace("<< rc %d", rc);
    if (unlikely(rc != MDBX_SUCCESS))
      mdbx_panic("%s() failed: err %d\n", __func__, rc);
    mdbx_jitter4testing(true);
  }
  
  #else
  #ifdef _MSC_VER
  #pragma warning(disable : 4206) /* nonstandard extension used: translation     \
                                     unit is empty */
  #endif                          /* _MSC_VER (warnings) */
  #endif                          /* !Windows LCK-implementation */
  