1 /* 2 * xlogdefs.h 3 * 4 * Postgres write-ahead log manager record pointer and 5 * timeline number definitions 6 * 7 * Portions Copyright (c) 1996-2019, 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 * XLogSegNo - physical log file sequence number. 40 */ 41 typedef uint64 XLogSegNo; 42 43 /* 44 * TimeLineID (TLI) - identifies different database histories to prevent 45 * confusion after restoring a prior state of a database installation. 46 * TLI does not change in a normal stop/restart of the database (including 47 * crash-and-recover cases); but we must assign a new TLI after doing 48 * a recovery to a prior state, a/k/a point-in-time recovery. This makes 49 * the new WAL logfile sequence we generate distinguishable from the 50 * sequence that was generated in the previous incarnation. 51 */ 52 typedef uint32 TimeLineID; 53 54 /* 55 * Replication origin id - this is located in this file to avoid having to 56 * include origin.h in a bunch of xlog related places. 57 */ 58 typedef uint16 RepOriginId; 59 60 /* 61 * Because O_DIRECT bypasses the kernel buffers, and because we never 62 * read those buffers except during crash recovery or if wal_level != minimal, 63 * it is a win to use it in all cases where we sync on each write(). We could 64 * allow O_DIRECT with fsync(), but it is unclear if fsync() could process 65 * writes not buffered in the kernel. Also, O_DIRECT is never enough to force 66 * data to the drives, it merely tries to bypass the kernel cache, so we still 67 * need O_SYNC/O_DSYNC. 68 */ 69 #ifdef O_DIRECT 70 #define PG_O_DIRECT O_DIRECT 71 #else 72 #define PG_O_DIRECT 0 73 #endif 74 75 /* 76 * This chunk of hackery attempts to determine which file sync methods 77 * are available on the current platform, and to choose an appropriate 78 * default method. We assume that fsync() is always available, and that 79 * configure determined whether fdatasync() is. 80 */ 81 #if defined(O_SYNC) 82 #define OPEN_SYNC_FLAG O_SYNC 83 #elif defined(O_FSYNC) 84 #define OPEN_SYNC_FLAG O_FSYNC 85 #endif 86 87 #if defined(O_DSYNC) 88 #if defined(OPEN_SYNC_FLAG) 89 /* O_DSYNC is distinct? */ 90 #if O_DSYNC != OPEN_SYNC_FLAG 91 #define OPEN_DATASYNC_FLAG O_DSYNC 92 #endif 93 #else /* !defined(OPEN_SYNC_FLAG) */ 94 /* Win32 only has O_DSYNC */ 95 #define OPEN_DATASYNC_FLAG O_DSYNC 96 #endif 97 #endif 98 99 #if defined(PLATFORM_DEFAULT_SYNC_METHOD) 100 #define DEFAULT_SYNC_METHOD PLATFORM_DEFAULT_SYNC_METHOD 101 #elif defined(OPEN_DATASYNC_FLAG) 102 #define DEFAULT_SYNC_METHOD SYNC_METHOD_OPEN_DSYNC 103 #elif defined(HAVE_FDATASYNC) 104 #define DEFAULT_SYNC_METHOD SYNC_METHOD_FDATASYNC 105 #else 106 #define DEFAULT_SYNC_METHOD SYNC_METHOD_FSYNC 107 #endif 108 109 #endif /* XLOG_DEFS_H */ 110