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/*-------------------------------------------------------------------------
*
* snapshot.h
* POSTGRES snapshot definition
*
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/utils/snapshot.h,v 1.1 2008/03/26 16:20:48 alvherre Exp $
*
*-------------------------------------------------------------------------
*/
#ifndef SNAPSHOT_H
#define SNAPSHOT_H
#include "access/htup.h"
#include "storage/buf.h"
typedef struct SnapshotData *Snapshot;
#define InvalidSnapshot ((Snapshot) NULL)
/*
* We use SnapshotData structures to represent both "regular" (MVCC)
* snapshots and "special" snapshots that have non-MVCC semantics.
* The specific semantics of a snapshot are encoded by the "satisfies"
* function.
*/
typedef bool (*SnapshotSatisfiesFunc) (HeapTupleHeader tuple,
Snapshot snapshot, Buffer buffer);
typedef struct SnapshotData
{
SnapshotSatisfiesFunc satisfies; /* tuple test function */
/*
* The remaining fields are used only for MVCC snapshots, and are normally
* just zeroes in special snapshots. (But xmin and xmax are used
* specially by HeapTupleSatisfiesDirty.)
*
* An MVCC snapshot can never see the effects of XIDs >= xmax. It can see
* the effects of all older XIDs except those listed in the snapshot. xmin
* is stored as an optimization to avoid needing to search the XID arrays
* for most tuples.
*/
TransactionId xmin; /* all XID < xmin are visible to me */
TransactionId xmax; /* all XID >= xmax are invisible to me */
uint32 xcnt; /* # of xact ids in xip[] */
TransactionId *xip; /* array of xact IDs in progress */
/* note: all ids in xip[] satisfy xmin <= xip[i] < xmax */
int32 subxcnt; /* # of xact ids in subxip[], -1 if overflow */
TransactionId *subxip; /* array of subxact IDs in progress */
/*
* note: all ids in subxip[] are >= xmin, but we don't bother filtering
* out any that are >= xmax
*/
CommandId curcid; /* in my xact, CID < curcid are visible */
} SnapshotData;
#endif /* SNAPSHOT_H */
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