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60 lines
1.9 KiB
C
60 lines
1.9 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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* system startup number definitions
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*
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* Portions Copyright (c) 1996-2001, 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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* $Id: xlogdefs.h,v 1.6 2001/10/28 06:25:59 momjian Exp $
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*/
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#ifndef XLOG_DEFS_H
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#define XLOG_DEFS_H
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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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/*
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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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* StartUpID (SUI) - system startups counter. It's to allow removing
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* pg_clog after shutdown, in future.
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*/
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typedef uint32 StartUpID;
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#endif /* XLOG_DEFS_H */
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