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145 lines
4.5 KiB
C
145 lines
4.5 KiB
C
/*
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* xlogdefs.h
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*
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* Postgres transaction log manager record pointer and
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* timeline number definitions
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*
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* Portions Copyright (c) 1996-2011, 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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* NOTE: xrecoff == 0 is used to indicate an invalid pointer. This is OK
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* because we use page headers in the XLOG, so no XLOG record can start
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* right at the beginning of a file.
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*
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* NOTE: the "log file number" is somewhat misnamed, since the actual files
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* making up the XLOG are much smaller than 4Gb. Each actual file is an
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* XLogSegSize-byte "segment" of a logical log file having the indicated
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* xlogid. The log file number and segment number together identify a
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* physical XLOG file. Segment number and offset within the physical file
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* are computed from xrecoff div and mod XLogSegSize.
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*/
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typedef struct XLogRecPtr
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{
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uint32 xlogid; /* log file #, 0 based */
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uint32 xrecoff; /* byte offset of location in log file */
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} XLogRecPtr;
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#define XLogRecPtrIsInvalid(r) ((r).xrecoff == 0)
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/*
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* Macros for comparing XLogRecPtrs
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*
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* Beware of passing expressions with side-effects to these macros,
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* since the arguments may be evaluated multiple times.
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*/
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#define XLByteLT(a, b) \
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((a).xlogid < (b).xlogid || \
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((a).xlogid == (b).xlogid && (a).xrecoff < (b).xrecoff))
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#define XLByteLE(a, b) \
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((a).xlogid < (b).xlogid || \
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((a).xlogid == (b).xlogid && (a).xrecoff <= (b).xrecoff))
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#define XLByteEQ(a, b) \
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((a).xlogid == (b).xlogid && (a).xrecoff == (b).xrecoff)
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/*
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* Macro for advancing a record pointer by the specified number of bytes.
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*/
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#define XLByteAdvance(recptr, nbytes) \
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do { \
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if (recptr.xrecoff + nbytes >= XLogFileSize) \
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{ \
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recptr.xlogid += 1; \
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recptr.xrecoff \
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= recptr.xrecoff + nbytes - XLogFileSize; \
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} \
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else \
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recptr.xrecoff += nbytes; \
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} while (0)
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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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* 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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/*
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* Limitation of buffer-alignment for direct IO depends on OS and filesystem,
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* but XLOG_BLCKSZ is assumed to be enough for it.
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*/
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#ifdef O_DIRECT
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#define ALIGNOF_XLOG_BUFFER XLOG_BLCKSZ
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#else
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#define ALIGNOF_XLOG_BUFFER ALIGNOF_BUFFER
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#endif
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#endif /* XLOG_DEFS_H */
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