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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 */