110 lines
3.3 KiB
C
110 lines
3.3 KiB
C
/*
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* xlogdefs.h
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*
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* Postgres write-ahead log manager record pointer and
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* timeline number definitions
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*
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* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/access/xlogdefs.h
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*/
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#ifndef XLOG_DEFS_H
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#define XLOG_DEFS_H
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#include <fcntl.h> /* need open() flags */
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/*
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* Pointer to a location in the XLOG. These pointers are 64 bits wide,
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* because we don't want them ever to overflow.
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*/
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typedef uint64 XLogRecPtr;
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/*
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* Zero is used indicate an invalid pointer. Bootstrap skips the first possible
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* WAL segment, initializing the first WAL page at WAL segment size, so no XLOG
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* record can begin at zero.
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*/
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#define InvalidXLogRecPtr 0
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#define XLogRecPtrIsInvalid(r) ((r) == InvalidXLogRecPtr)
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/*
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* First LSN to use for "fake" LSNs.
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*
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* Values smaller than this can be used for special per-AM purposes.
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*/
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#define FirstNormalUnloggedLSN ((XLogRecPtr) 1000)
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/*
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* XLogSegNo - physical log file sequence number.
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*/
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typedef uint64 XLogSegNo;
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/*
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* TimeLineID (TLI) - identifies different database histories to prevent
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* confusion after restoring a prior state of a database installation.
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* TLI does not change in a normal stop/restart of the database (including
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* crash-and-recover cases); but we must assign a new TLI after doing
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* a recovery to a prior state, a/k/a point-in-time recovery. This makes
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* the new WAL logfile sequence we generate distinguishable from the
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* sequence that was generated in the previous incarnation.
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*/
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typedef uint32 TimeLineID;
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/*
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* Replication origin id - this is located in this file to avoid having to
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* include origin.h in a bunch of xlog related places.
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*/
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typedef uint16 RepOriginId;
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/*
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* Because O_DIRECT bypasses the kernel buffers, and because we never
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* read those buffers except during crash recovery or if wal_level != minimal,
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* it is a win to use it in all cases where we sync on each write(). We could
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* allow O_DIRECT with fsync(), but it is unclear if fsync() could process
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* writes not buffered in the kernel. Also, O_DIRECT is never enough to force
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* data to the drives, it merely tries to bypass the kernel cache, so we still
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* need O_SYNC/O_DSYNC.
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*/
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#ifdef O_DIRECT
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#define PG_O_DIRECT O_DIRECT
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#else
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#define PG_O_DIRECT 0
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#endif
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/*
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* This chunk of hackery attempts to determine which file sync methods
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* are available on the current platform, and to choose an appropriate
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* default method. We assume that fsync() is always available, and that
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* configure determined whether fdatasync() is.
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*/
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#if defined(O_SYNC)
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#define OPEN_SYNC_FLAG O_SYNC
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#elif defined(O_FSYNC)
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#define OPEN_SYNC_FLAG O_FSYNC
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#endif
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#if defined(O_DSYNC)
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#if defined(OPEN_SYNC_FLAG)
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/* O_DSYNC is distinct? */
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#if O_DSYNC != OPEN_SYNC_FLAG
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#define OPEN_DATASYNC_FLAG O_DSYNC
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#endif
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#else /* !defined(OPEN_SYNC_FLAG) */
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/* Win32 only has O_DSYNC */
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#define OPEN_DATASYNC_FLAG O_DSYNC
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#endif
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#endif
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#if defined(PLATFORM_DEFAULT_SYNC_METHOD)
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#define DEFAULT_SYNC_METHOD PLATFORM_DEFAULT_SYNC_METHOD
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#elif defined(OPEN_DATASYNC_FLAG)
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#define DEFAULT_SYNC_METHOD SYNC_METHOD_OPEN_DSYNC
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#elif defined(HAVE_FDATASYNC)
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#define DEFAULT_SYNC_METHOD SYNC_METHOD_FDATASYNC
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#else
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#define DEFAULT_SYNC_METHOD SYNC_METHOD_FSYNC
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#endif
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#endif /* XLOG_DEFS_H */
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