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).
   *
   * $PostgreSQL: pgsql/src/include/pg_config_manual.h,v 1.27 2007/06/08 18:23:53 tgl Exp $
   *------------------------------------------------------------------------
   */
  
  /*
   * Size of a disk block --- this also limits the size of a tuple.  You
   * can set it bigger if you need bigger tuples (although TOAST should
   * reduce the need to have large tuples, since fields can be spread
   * across multiple tuples).
   *
   * BLCKSZ must be a power of 2.  The maximum possible value of BLCKSZ
   * is currently 2^15 (32768).  This is determined by the 15-bit widths
   * of the lp_off and lp_len fields in ItemIdData (see
   * include/storage/itemid.h).
   *
   * Changing BLCKSZ requires an initdb.
   */
  #define BLCKSZ	8192
  
  /*
   * RELSEG_SIZE is the maximum number of blocks allowed in one disk
   * file.  Thus, the maximum size of a single file is RELSEG_SIZE *
   * BLCKSZ; relations bigger than that are divided into multiple files.
   *
   * RELSEG_SIZE * BLCKSZ must be less than your OS' limit on file size.
   * This is often 2 GB or 4GB in a 32-bit operating system, unless you
   * have large file support enabled.  By default, we make the limit 1
   * GB to avoid any possible integer-overflow problems within the OS.
   * A limit smaller than necessary only means we divide a large
   * relation into more chunks than necessary, so it seems best to err
   * in the direction of a small limit.  (Besides, a power-of-2 value
   * saves a few cycles in md.c.)
   *
   * Changing RELSEG_SIZE requires an initdb.
   */
  #define RELSEG_SIZE (0x40000000 / BLCKSZ)
  
  /*
   * Size of a WAL file block.  This need have no particular relation to BLCKSZ.
   * XLOG_BLCKSZ must be a power of 2, and if your system supports O_DIRECT I/O,
   * XLOG_BLCKSZ must be a multiple of the alignment requirement for direct-I/O
   * buffers, else direct I/O may fail.
   *
   * Changing XLOG_BLCKSZ requires an initdb.
   */
  #define XLOG_BLCKSZ		8192
  
  /*
   * XLOG_SEG_SIZE is the size of a single WAL file.	This must be a power of 2
   * and larger than XLOG_BLCKSZ (preferably, a great deal larger than
   * XLOG_BLCKSZ).
   *
   * Changing XLOG_SEG_SIZE requires an initdb.
   */
  #define XLOG_SEG_SIZE	(16*1024*1024)
  
  /*
   * Maximum length for identifiers (e.g. table names, column names,
   * function names).  It must be a multiple of sizeof(int) (typically
   * 4).
   *
   * Changing this requires an initdb.
   */
  #define NAMEDATALEN 64
  
  /*
   * Maximum number of arguments to a function.
   *
   * The minimum value is 8 (index cost estimation uses 8-argument 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
  
  /*
   * Number of spare LWLocks to allocate for user-defined add-on code.
   */
  #define NUM_USER_DEFINED_LWLOCKS	4
  
  /*
   * Define this to make libpgtcl's "pg_result -assign" command process
   * C-style backslash sequences in returned tuple data and convert
   * PostgreSQL array values into Tcl lists.	CAUTION: This conversion
   * is *wrong* unless you install the routines in
   * contrib/string/string_io to make the server produce C-style
   * backslash sequences in the first place.
   */
  /* #define TCL_ARRAYS */
  
  /*
   * Define this if you want psql to _always_ ask for a username and a
   * password for password authentication.
   */
  /* #define PSQL_ALWAYS_GET_PASSWORDS */
  
  /*
   * Define this if you want to allow the lo_import and lo_export SQL
   * functions to be executed by ordinary users.	By default these
   * functions are only available to the Postgres superuser.	CAUTION:
   * These functions are SECURITY HOLES since they can read and write
   * any file that the PostgreSQL server has permission to access.  If
   * you turn this on, don't say we didn't warn you.
   */
  /* #define ALLOW_DANGEROUS_LO_FUNCTIONS */
  
  /*
   * 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
  
  /*
   * Disable UNIX sockets for those operating system.
   */
  #if defined(WIN32)
  #undef HAVE_UNIX_SOCKETS
  #endif
  
  /*
   * Define this if your operating system supports link()
   */
  #if !defined(WIN32) && !defined(__CYGWIN__)
  #define HAVE_WORKING_LINK 1
  #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.
   */
  #define DEFAULT_PGSOCKET_DIR  "/tmp"
  
  /*
   * 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  (0x7FFFFFFF)
  
  
  /*
   *------------------------------------------------------------------------
   * The following symbols are for enabling debugging code, not for
   * controlling user-visible features or resource limits.
   *------------------------------------------------------------------------
   */
  
  /*
   * Define this to cause pfree()'d memory to be cleared immediately, to
   * facilitate catching bugs that refer to already-freed values.  XXX
   * Right now, this gets defined automatically if --enable-cassert.	In
   * the long term it probably doesn't need to be on by default.
   */
  #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.  In the long term it probably
   * doesn't need to be on by default.
   */
  #ifdef USE_ASSERT_CHECKING
  #define MEMORY_CONTEXT_CHECKING
  #endif
  
  /*
   * 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 */
  
  /*
   * 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 HEAPDEBUGALL */
  /* #define ACLDEBUG */
  /* #define RTDEBUG */
  