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/*
* xlogdefs.h
*
* Postgres write-ahead log manager record pointer and
* timeline number definitions
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/access/xlogdefs.h
*/
#ifndef XLOG_DEFS_H
#define XLOG_DEFS_H
#include <fcntl.h> /* need open() flags */
/*
* Pointer to a location in the XLOG. These pointers are 64 bits wide,
* because we don't want them ever to overflow.
*/
typedef uint64 XLogRecPtr;
/*
* Zero is used indicate an invalid pointer. Bootstrap skips the first possible
* WAL segment, initializing the first WAL page at WAL segment size, so no XLOG
* record can begin at zero.
*/
#define InvalidXLogRecPtr 0
#define XLogRecPtrIsInvalid(r) ((r) == InvalidXLogRecPtr)
/*
* First LSN to use for "fake" LSNs.
*
* Values smaller than this can be used for special per-AM purposes.
*/
#define FirstNormalUnloggedLSN ((XLogRecPtr) 1000)
/*
* XLogSegNo - physical log file sequence number.
*/
typedef uint64 XLogSegNo;
/*
* TimeLineID (TLI) - identifies different database histories to prevent
* confusion after restoring a prior state of a database installation.
* TLI does not change in a normal stop/restart of the database (including
* crash-and-recover cases); but we must assign a new TLI after doing
* a recovery to a prior state, a/k/a point-in-time recovery. This makes
* the new WAL logfile sequence we generate distinguishable from the
* sequence that was generated in the previous incarnation.
*/
typedef uint32 TimeLineID;
/*
* Replication origin id - this is located in this file to avoid having to
* include origin.h in a bunch of xlog related places.
*/
typedef uint16 RepOriginId;
/*
* Because O_DIRECT bypasses the kernel buffers, and because we never
* read those buffers except during crash recovery or if wal_level != minimal,
* it is a win to use it in all cases where we sync on each write(). We could
* allow O_DIRECT with fsync(), but it is unclear if fsync() could process
* writes not buffered in the kernel. Also, O_DIRECT is never enough to force
* data to the drives, it merely tries to bypass the kernel cache, so we still
* need O_SYNC/O_DSYNC.
*/
#ifdef O_DIRECT
#define PG_O_DIRECT O_DIRECT
#else
#define PG_O_DIRECT 0
#endif
/*
* This chunk of hackery attempts to determine which file sync methods
* are available on the current platform, and to choose an appropriate
* default method. We assume that fsync() is always available, and that
* configure determined whether fdatasync() is.
*/
#if defined(O_SYNC)
#define OPEN_SYNC_FLAG O_SYNC
#elif defined(O_FSYNC)
#define OPEN_SYNC_FLAG O_FSYNC
#endif
#if defined(O_DSYNC)
#if defined(OPEN_SYNC_FLAG)
/* O_DSYNC is distinct? */
#if O_DSYNC != OPEN_SYNC_FLAG
#define OPEN_DATASYNC_FLAG O_DSYNC
#endif
#else /* !defined(OPEN_SYNC_FLAG) */
/* Win32 only has O_DSYNC */
#define OPEN_DATASYNC_FLAG O_DSYNC
#endif
#endif
#if defined(PLATFORM_DEFAULT_SYNC_METHOD)
#define DEFAULT_SYNC_METHOD PLATFORM_DEFAULT_SYNC_METHOD
#elif defined(OPEN_DATASYNC_FLAG)
#define DEFAULT_SYNC_METHOD SYNC_METHOD_OPEN_DSYNC
#elif defined(HAVE_FDATASYNC)
#define DEFAULT_SYNC_METHOD SYNC_METHOD_FDATASYNC
#else
#define DEFAULT_SYNC_METHOD SYNC_METHOD_FSYNC
#endif
#endif /* XLOG_DEFS_H */
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