src/include/access/xlogdefs.h

   1 /*
   2  * xlogdefs.h
   3  *
   4  * Postgres write-ahead log manager record pointer and
   5  * timeline number definitions
   6  *
   7  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * src/include/access/xlogdefs.h
  11  */
  12 #ifndef XLOG_DEFS_H
  13 #define XLOG_DEFS_H
  14
  15 #include <fcntl.h>                              /* need open() flags */
  16
  17 /*
  18  * Pointer to a location in the XLOG.  These pointers are 64 bits wide,
  19  * because we don't want them ever to overflow.
  20  */
  21 typedef uint64 XLogRecPtr;
  22
  23 /*
  24  * Zero is used indicate an invalid pointer. Bootstrap skips the first possible
  25  * WAL segment, initializing the first WAL page at WAL segment size, so no XLOG
  26  * record can begin at zero.
  27  */
  28 #define InvalidXLogRecPtr       0
  29 #define XLogRecPtrIsInvalid(r)  ((r) == InvalidXLogRecPtr)
  30
  31 /*
  32  * First LSN to use for "fake" LSNs.
  33  *
  34  * Values smaller than this can be used for special per-AM purposes.
  35  */
  36 #define FirstNormalUnloggedLSN  ((XLogRecPtr) 1000)
  37
  38 /*
  39  * Handy macro for printing XLogRecPtr in conventional format, e.g.,
  40  *
  41  * printf("%X/%X", LSN_FORMAT_ARGS(lsn));
  42  */
  43 #define LSN_FORMAT_ARGS(lsn) (AssertVariableIsOfTypeMacro((lsn), XLogRecPtr), (uint32) ((lsn) >> 32)), ((uint32) (lsn))
  44
  45 /*
  46  * XLogSegNo - physical log file sequence number.
  47  */
  48 typedef uint64 XLogSegNo;
  49
  50 /*
  51  * TimeLineID (TLI) - identifies different database histories to prevent
  52  * confusion after restoring a prior state of a database installation.
  53  * TLI does not change in a normal stop/restart of the database (including
  54  * crash-and-recover cases); but we must assign a new TLI after doing
  55  * a recovery to a prior state, a/k/a point-in-time recovery.  This makes
  56  * the new WAL logfile sequence we generate distinguishable from the
  57  * sequence that was generated in the previous incarnation.
  58  */
  59 typedef uint32 TimeLineID;
  60
  61 /*
  62  * Replication origin id - this is located in this file to avoid having to
  63  * include origin.h in a bunch of xlog related places.
  64  */
  65 typedef uint16 RepOriginId;
  66
  67 /*
  68  * This chunk of hackery attempts to determine which file sync methods
  69  * are available on the current platform, and to choose an appropriate
  70  * default method.  We assume that fsync() is always available, and that
  71  * configure determined whether fdatasync() is.
  72  */
  73 #if defined(O_SYNC)
  74 #define OPEN_SYNC_FLAG          O_SYNC
  75 #elif defined(O_FSYNC)
  76 #define OPEN_SYNC_FLAG          O_FSYNC
  77 #endif
  78
  79 #if defined(O_DSYNC)
  80 #if defined(OPEN_SYNC_FLAG)
  81 /* O_DSYNC is distinct? */
  82 #if O_DSYNC != OPEN_SYNC_FLAG
  83 #define OPEN_DATASYNC_FLAG              O_DSYNC
  84 #endif
  85 #else                                                   /* !defined(OPEN_SYNC_FLAG) */
  86 /* Win32 only has O_DSYNC */
  87 #define OPEN_DATASYNC_FLAG              O_DSYNC
  88 #endif
  89 #endif
  90
  91 #if defined(PLATFORM_DEFAULT_SYNC_METHOD)
  92 #define DEFAULT_SYNC_METHOD             PLATFORM_DEFAULT_SYNC_METHOD
  93 #elif defined(OPEN_DATASYNC_FLAG)
  94 #define DEFAULT_SYNC_METHOD             SYNC_METHOD_OPEN_DSYNC
  95 #elif defined(HAVE_FDATASYNC)
  96 #define DEFAULT_SYNC_METHOD             SYNC_METHOD_FDATASYNC
  97 #else
  98 #define DEFAULT_SYNC_METHOD             SYNC_METHOD_FSYNC
  99 #endif
 100
 101 #endif                                                  /* XLOG_DEFS_H */