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/*
* xlogdefs.h
*
* Postgres transaction log manager record pointer and
* timeline number definitions
*
* Portions Copyright (c) 1996-2012, 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.
*
* NOTE: xrecoff == 0 is used to indicate an invalid pointer. This is OK
* because we use page headers in the XLOG, so no XLOG record can start
* right at the beginning of a file.
*
* NOTE: the "log file number" is somewhat misnamed, since the actual files
* making up the XLOG are much smaller than 4Gb. Each actual file is an
* XLogSegSize-byte "segment" of a logical log file having the indicated
* xlogid. The log file number and segment number together identify a
* physical XLOG file. Segment number and offset within the physical file
* are computed from xrecoff div and mod XLogSegSize.
*/
typedef struct XLogRecPtr
{
uint32 xlogid; /* log file #, 0 based */
uint32 xrecoff; /* byte offset of location in log file */
} XLogRecPtr;
#define XLogRecPtrIsInvalid(r) ((r).xrecoff == 0)
/*
* Macros for comparing XLogRecPtrs
*
* Beware of passing expressions with side-effects to these macros,
* since the arguments may be evaluated multiple times.
*/
#define XLByteLT(a, b) \
((a).xlogid < (b).xlogid || \
((a).xlogid == (b).xlogid && (a).xrecoff < (b).xrecoff))
#define XLByteLE(a, b) \
((a).xlogid < (b).xlogid || \
((a).xlogid == (b).xlogid && (a).xrecoff <= (b).xrecoff))
#define XLByteEQ(a, b) \
((a).xlogid == (b).xlogid && (a).xrecoff == (b).xrecoff)
/*
* Macro for advancing a record pointer by the specified number of bytes.
*/
#define XLByteAdvance(recptr, nbytes) \
do { \
if (recptr.xrecoff + nbytes >= XLogFileSize) \
{ \
recptr.xlogid += 1; \
recptr.xrecoff \
= recptr.xrecoff + nbytes - XLogFileSize; \
} \
else \
recptr.xrecoff += nbytes; \
} while (0)
/*
* 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;
/*
* 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
/*
* Limitation of buffer-alignment for direct IO depends on OS and filesystem,
* but XLOG_BLCKSZ is assumed to be enough for it.
*/
#ifdef O_DIRECT
#define ALIGNOF_XLOG_BUFFER XLOG_BLCKSZ
#else
#define ALIGNOF_XLOG_BUFFER ALIGNOF_BUFFER
#endif
#endif /* XLOG_DEFS_H */
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