text: /*------------------------------------------------------------------------
   * PostgreSQL manual configuration settings
   *
   * This file contains various configuration symbols and limits.  In
   * all cases, changing them is only useful in very rare situations or
   * for developers.  If you edit any of these, be sure to do a *full*
   * rebuild (and an initdb if noted).
   *
   * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * src/include/pg_config_manual.h
   *------------------------------------------------------------------------
   */
  
  /*
   * This is the default value for wal_segment_size to be used when initdb is run
   * without the --wal-segsize option.  It must be a valid segment size.
   */
  #define DEFAULT_XLOG_SEG_SIZE	(16*1024*1024)
  
  /*
   * Maximum length for identifiers (e.g. table names, column names,
   * function names).  Names actually are limited to one less byte than this,
   * because the length must include a trailing zero byte.
   *
   * Changing this requires an initdb.
   */
  #define NAMEDATALEN 64
  
  /*
   * Maximum number of arguments to a function.
   *
   * The minimum value is 8 (GIN indexes use 8-argument support functions).
   * The maximum possible value is around 600 (limited by index tuple size in
   * pg_proc's index; BLCKSZ larger than 8K would allow more).  Values larger
   * than needed will waste memory and processing time, but do not directly
   * cost disk space.
   *
   * Changing this does not require an initdb, but it does require a full
   * backend recompile (including any user-defined C functions).
   */
  #define FUNC_MAX_ARGS		100
  
  /*
   * Maximum number of columns in an index.  There is little point in making
   * this anything but a multiple of 32, because the main cost is associated
   * with index tuple header size (see access/itup.h).
   *
   * Changing this requires an initdb.
   */
  #define INDEX_MAX_KEYS		32
  
  /*
   * Maximum number of columns in a partition key
   */
  #define PARTITION_MAX_KEYS	32
  
  /*
   * Decide whether built-in 8-byte types, including float8, int8, and
   * timestamp, are passed by value.  This is on by default if sizeof(Datum) >=
   * 8 (that is, on 64-bit platforms).  If sizeof(Datum) < 8 (32-bit platforms),
   * this must be off.  We keep this here as an option so that it is easy to
   * test the pass-by-reference code paths on 64-bit platforms.
   *
   * Changing this requires an initdb.
   */
  #if SIZEOF_VOID_P >= 8
  #define USE_FLOAT8_BYVAL 1
  #endif
  
  /*
   * When we don't have native spinlocks, we use semaphores to simulate them.
   * Decreasing this value reduces consumption of OS resources; increasing it
   * may improve performance, but supplying a real spinlock implementation is
   * probably far better.
   */
  #define NUM_SPINLOCK_SEMAPHORES		128
  
  /*
   * When we have neither spinlocks nor atomic operations support we're
   * implementing atomic operations on top of spinlock on top of semaphores. To
   * be safe against atomic operations while holding a spinlock separate
   * semaphores have to be used.
   */
  #define NUM_ATOMICS_SEMAPHORES		64
  
  /*
   * MAXPGPATH: standard size of a pathname buffer in PostgreSQL (hence,
   * maximum usable pathname length is one less).
   *
   * We'd use a standard system header symbol for this, if there weren't
   * so many to choose from: MAXPATHLEN, MAX_PATH, PATH_MAX are all
   * defined by different "standards", and often have different values
   * on the same platform!  So we just punt and use a reasonably
   * generous setting here.
   */
  #define MAXPGPATH		1024
  
  /*
   * PG_SOMAXCONN: maximum accept-queue length limit passed to
   * listen(2).  You'd think we should use SOMAXCONN from
   * <sys/socket.h>, but on many systems that symbol is much smaller
   * than the kernel's actual limit.  In any case, this symbol need be
   * twiddled only if you have a kernel that refuses large limit values,
   * rather than silently reducing the value to what it can handle
   * (which is what most if not all Unixen do).
   */
  #define PG_SOMAXCONN	10000
  
  /*
   * You can try changing this if you have a machine with bytes of
   * another size, but no guarantee...
   */
  #define BITS_PER_BYTE		8
  
  /*
   * Preferred alignment for disk I/O buffers.  On some CPUs, copies between
   * user space and kernel space are significantly faster if the user buffer
   * is aligned on a larger-than-MAXALIGN boundary.  Ideally this should be
   * a platform-dependent value, but for now we just hard-wire it.
   */
  #define ALIGNOF_BUFFER	32
  
  /*
   * If EXEC_BACKEND is defined, the postmaster uses an alternative method for
   * starting subprocesses: Instead of simply using fork(), as is standard on
   * Unix platforms, it uses fork()+exec() or something equivalent on Windows,
   * as well as lots of extra code to bring the required global state to those
   * new processes.  This must be enabled on Windows (because there is no
   * fork()).  On other platforms, it's only useful for verifying those
   * otherwise Windows-specific code paths.
   */
  #if defined(WIN32) && !defined(__CYGWIN__)
  #define EXEC_BACKEND
  #endif
  
  /*
   * USE_POSIX_FADVISE controls whether Postgres will attempt to use the
   * posix_fadvise() kernel call.  Usually the automatic configure tests are
   * sufficient, but some older Linux distributions had broken versions of
   * posix_fadvise().  If necessary you can remove the #define here.
   */
  #if HAVE_DECL_POSIX_FADVISE && defined(HAVE_POSIX_FADVISE)
  #define USE_POSIX_FADVISE
  #endif
  
  /*
   * USE_PREFETCH code should be compiled only if we have a way to implement
   * prefetching.  (This is decoupled from USE_POSIX_FADVISE because there
   * might in future be support for alternative low-level prefetch APIs.
   * If you change this, you probably need to adjust the error message in
   * check_effective_io_concurrency.)
   */
  #ifdef USE_POSIX_FADVISE
  #define USE_PREFETCH
  #endif
  
  /*
   * Default and maximum values for backend_flush_after, bgwriter_flush_after
   * and checkpoint_flush_after; measured in blocks.  Currently, these are
   * enabled by default if sync_file_range() exists, ie, only on Linux.  Perhaps
   * we could also enable by default if we have mmap and msync(MS_ASYNC)?
   */
  #ifdef HAVE_SYNC_FILE_RANGE
  #define DEFAULT_BACKEND_FLUSH_AFTER 0	/* never enabled by default */
  #define DEFAULT_BGWRITER_FLUSH_AFTER 64
  #define DEFAULT_CHECKPOINT_FLUSH_AFTER 32
  #else
  #define DEFAULT_BACKEND_FLUSH_AFTER 0
  #define DEFAULT_BGWRITER_FLUSH_AFTER 0
  #define DEFAULT_CHECKPOINT_FLUSH_AFTER 0
  #endif
  /* upper limit for all three variables */
  #define WRITEBACK_MAX_PENDING_FLUSHES 256
  
  /*
   * USE_SSL code should be compiled only when compiling with an SSL
   * implementation.  (Currently, only OpenSSL is supported, but we might add
   * more implementations in the future.)
   */
  #ifdef USE_OPENSSL
  #define USE_SSL
  #endif
  
  /*
   * This is the default directory in which AF_UNIX socket files are
   * placed.  Caution: changing this risks breaking your existing client
   * applications, which are likely to continue to look in the old
   * directory.  But if you just hate the idea of sockets in /tmp,
   * here's where to twiddle it.  You can also override this at runtime
   * with the postmaster's -k switch.
   *
   * If set to an empty string, then AF_UNIX sockets are not used by default: A
   * server will not create an AF_UNIX socket unless the run-time configuration
   * is changed, a client will connect via TCP/IP by default and will only use
   * an AF_UNIX socket if one is explicitly specified.
   *
   * This is done by default on Windows because there is no good standard
   * location for AF_UNIX sockets and many installations on Windows don't
   * support them yet.
   */
  #ifndef WIN32
  #define DEFAULT_PGSOCKET_DIR  "/tmp"
  #else
  #define DEFAULT_PGSOCKET_DIR ""
  #endif
  
  /*
   * This is the default event source for Windows event log.
   */
  #define DEFAULT_EVENT_SOURCE  "PostgreSQL"
  
  /*
   * The random() function is expected to yield values between 0 and
   * MAX_RANDOM_VALUE.  Currently, all known implementations yield
   * 0..2^31-1, so we just hardwire this constant.  We could do a
   * configure test if it proves to be necessary.  CAUTION: Think not to
   * replace this with RAND_MAX.  RAND_MAX defines the maximum value of
   * the older rand() function, which is often different from --- and
   * considerably inferior to --- random().
   */
  #define MAX_RANDOM_VALUE  PG_INT32_MAX
  
  /*
   * On PPC machines, decide whether to use the mutex hint bit in LWARX
   * instructions.  Setting the hint bit will slightly improve spinlock
   * performance on POWER6 and later machines, but does nothing before that,
   * and will result in illegal-instruction failures on some pre-POWER4
   * machines.  By default we use the hint bit when building for 64-bit PPC,
   * which should be safe in nearly all cases.  You might want to override
   * this if you are building 32-bit code for a known-recent PPC machine.
   */
  #ifdef HAVE_PPC_LWARX_MUTEX_HINT	/* must have assembler support in any case */
  #if defined(__ppc64__) || defined(__powerpc64__)
  #define USE_PPC_LWARX_MUTEX_HINT
  #endif
  #endif
  
  /*
   * On PPC machines, decide whether to use LWSYNC instructions in place of
   * ISYNC and SYNC.  This provides slightly better performance, but will
   * result in illegal-instruction failures on some pre-POWER4 machines.
   * By default we use LWSYNC when building for 64-bit PPC, which should be
   * safe in nearly all cases.
   */
  #if defined(__ppc64__) || defined(__powerpc64__)
  #define USE_PPC_LWSYNC
  #endif
  
  /*
   * Assumed cache line size. This doesn't affect correctness, but can be used
   * for low-level optimizations. Currently, this is used to pad some data
   * structures in xlog.c, to ensure that highly-contended fields are on
   * different cache lines. Too small a value can hurt performance due to false
   * sharing, while the only downside of too large a value is a few bytes of
   * wasted memory. The default is 128, which should be large enough for all
   * supported platforms.
   */
  #define PG_CACHE_LINE_SIZE		128
  
  /*
   *------------------------------------------------------------------------
   * The following symbols are for enabling debugging code, not for
   * controlling user-visible features or resource limits.
   *------------------------------------------------------------------------
   */
  
  /*
   * Include Valgrind "client requests", mostly in the memory allocator, so
   * Valgrind understands PostgreSQL memory contexts.  This permits detecting
   * memory errors that Valgrind would not detect on a vanilla build.  See also
   * src/tools/valgrind.supp.  "make installcheck" runs 20-30x longer under
   * Valgrind.  Note that USE_VALGRIND slowed older versions of Valgrind by an
   * additional order of magnitude; Valgrind 3.8.1 does not have this problem.
   * The client requests fall in hot code paths, so USE_VALGRIND also slows
   * native execution by a few percentage points.
   *
   * You should normally use MEMORY_CONTEXT_CHECKING with USE_VALGRIND;
   * instrumentation of repalloc() is inferior without it.
   */
  /* #define USE_VALGRIND */
  
  /*
   * Define this to cause pfree()'d memory to be cleared immediately, to
   * facilitate catching bugs that refer to already-freed values.
   * Right now, this gets defined automatically if --enable-cassert.
   */
  #ifdef USE_ASSERT_CHECKING
  #define CLOBBER_FREED_MEMORY
  #endif
  
  /*
   * Define this to check memory allocation errors (scribbling on more
   * bytes than were allocated).  Right now, this gets defined
   * automatically if --enable-cassert or USE_VALGRIND.
   */
  #if defined(USE_ASSERT_CHECKING) || defined(USE_VALGRIND)
  #define MEMORY_CONTEXT_CHECKING
  #endif
  
  /*
   * Define this to cause palloc()'d memory to be filled with random data, to
   * facilitate catching code that depends on the contents of uninitialized
   * memory.  Caution: this is horrendously expensive.
   */
  /* #define RANDOMIZE_ALLOCATED_MEMORY */
  
  /*
   * Define this to force all parse and plan trees to be passed through
   * copyObject(), to facilitate catching errors and omissions in
   * copyObject().
   */
  /* #define COPY_PARSE_PLAN_TREES */
  
  /*
   * Define this to force all parse and plan trees to be passed through
   * outfuncs.c/readfuncs.c, to facilitate catching errors and omissions in
   * those modules.
   */
  /* #define WRITE_READ_PARSE_PLAN_TREES */
  
  /*
   * Define this to force all raw parse trees for DML statements to be scanned
   * by raw_expression_tree_walker(), to facilitate catching errors and
   * omissions in that function.
   */
  /* #define RAW_EXPRESSION_COVERAGE_TEST */
  
  /*
   * Enable debugging print statements for lock-related operations.
   */
  /* #define LOCK_DEBUG */
  
  /*
   * Enable debugging print statements for WAL-related operations; see
   * also the wal_debug GUC var.
   */
  /* #define WAL_DEBUG */
  
  /*
   * Enable tracing of resource consumption during sort operations;
   * see also the trace_sort GUC var.  For 8.1 this is enabled by default.
   */
  #define TRACE_SORT 1
  
  /*
   * Enable tracing of syncscan operations (see also the trace_syncscan GUC var).
   */
  /* #define TRACE_SYNCSCAN */
  
  /*
   * Other debug #defines (documentation, anyone?)
   */
  /* #define ACLDEBUG */
  