1 /* 2 * xlogdefs.h 3 * 4 * Postgres transaction log manager record pointer and 5 * timeline number definitions 6 * 7 * Portions Copyright (c) 1996-2016, 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 XLOG_SEG_SIZE, so no XLOG 26 * record can begin at zero. 27 */ 28 #define InvalidXLogRecPtr 0 29 #define XLogRecPtrIsInvalid(r) ((r) == InvalidXLogRecPtr) 30 31 /* 32 * XLogSegNo - physical log file sequence number. 33 */ 34 typedef uint64 XLogSegNo; 35 36 /* 37 * TimeLineID (TLI) - identifies different database histories to prevent 38 * confusion after restoring a prior state of a database installation. 39 * TLI does not change in a normal stop/restart of the database (including 40 * crash-and-recover cases); but we must assign a new TLI after doing 41 * a recovery to a prior state, a/k/a point-in-time recovery. This makes 42 * the new WAL logfile sequence we generate distinguishable from the 43 * sequence that was generated in the previous incarnation. 44 */ 45 typedef uint32 TimeLineID; 46 47 /* 48 * Replication origin id - this is located in this file to avoid having to 49 * include origin.h in a bunch of xlog related places. 50 */ 51 typedef uint16 RepOriginId; 52 53 /* 54 * Because O_DIRECT bypasses the kernel buffers, and because we never 55 * read those buffers except during crash recovery or if wal_level != minimal, 56 * it is a win to use it in all cases where we sync on each write(). We could 57 * allow O_DIRECT with fsync(), but it is unclear if fsync() could process 58 * writes not buffered in the kernel. Also, O_DIRECT is never enough to force 59 * data to the drives, it merely tries to bypass the kernel cache, so we still 60 * need O_SYNC/O_DSYNC. 61 */ 62 #ifdef O_DIRECT 63 #define PG_O_DIRECT O_DIRECT 64 #else 65 #define PG_O_DIRECT 0 66 #endif 67 68 /* 69 * This chunk of hackery attempts to determine which file sync methods 70 * are available on the current platform, and to choose an appropriate 71 * default method. We assume that fsync() is always available, and that 72 * configure determined whether fdatasync() is. 73 */ 74 #if defined(O_SYNC) 75 #define OPEN_SYNC_FLAG O_SYNC 76 #elif defined(O_FSYNC) 77 #define OPEN_SYNC_FLAG O_FSYNC 78 #endif 79 80 #if defined(O_DSYNC) 81 #if defined(OPEN_SYNC_FLAG) 82 /* O_DSYNC is distinct? */ 83 #if O_DSYNC != OPEN_SYNC_FLAG 84 #define OPEN_DATASYNC_FLAG O_DSYNC 85 #endif 86 #else /* !defined(OPEN_SYNC_FLAG) */ 87 /* Win32 only has O_DSYNC */ 88 #define OPEN_DATASYNC_FLAG O_DSYNC 89 #endif 90 #endif 91 92 #if defined(PLATFORM_DEFAULT_SYNC_METHOD) 93 #define DEFAULT_SYNC_METHOD PLATFORM_DEFAULT_SYNC_METHOD 94 #elif defined(OPEN_DATASYNC_FLAG) 95 #define DEFAULT_SYNC_METHOD SYNC_METHOD_OPEN_DSYNC 96 #elif defined(HAVE_FDATASYNC) 97 #define DEFAULT_SYNC_METHOD SYNC_METHOD_FDATASYNC 98 #else 99 #define DEFAULT_SYNC_METHOD SYNC_METHOD_FSYNC 100 #endif 101 102 #endif /* XLOG_DEFS_H */ 103