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/*
* xlogdefs.h
*
* Postgres transaction log manager record pointer and
* system startup number definitions
*
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: xlogdefs.h,v 1.5 2001/10/25 05:49:56 momjian Exp $
*/
#ifndef XLOG_DEFS_H
#define XLOG_DEFS_H
/*
* 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;
/*
* 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)
/*
* StartUpID (SUI) - system startups counter. It's to allow removing
* pg_clog after shutdown, in future.
*/
typedef uint32 StartUpID;
#endif /* XLOG_DEFS_H */
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