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Separate snapshot management code from tuple visibility code, create a
snapmgmt.c file for the former. The header files have also been reorganized in three parts: the most basic snapshot definitions are now in a new file snapshot.h, and the also new snapmgmt.h keeps the definitions for snapmgmt.c. tqual.h has been reduced to the bare minimum. This patch is just a first step towards managing live snapshots within a transaction; there is no functionality change. Per my proposal to pgsql-patches on 20080318191940.GB27458@alvh.no-ip.org and subsequent discussion.
This commit is contained in:
Alvaro Herrera
@@ -4,7 +4,7 @@
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# Makefile for utils/time
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#
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# IDENTIFICATION
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# $PostgreSQL: pgsql/src/backend/utils/time/Makefile,v 1.13 2008/02/19 10:30:09 petere Exp $
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# $PostgreSQL: pgsql/src/backend/utils/time/Makefile,v 1.14 2008/03/26 16:20:47 alvherre Exp $
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#
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#-------------------------------------------------------------------------
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@@ -12,6 +12,6 @@ subdir = src/backend/utils/time
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top_builddir = ../../../..
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include $(top_builddir)/src/Makefile.global
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OBJS = combocid.o tqual.o
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OBJS = combocid.o tqual.o snapmgmt.o
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include $(top_srcdir)/src/backend/common.mk
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172
src/backend/utils/time/snapmgmt.c
Normal file
172
src/backend/utils/time/snapmgmt.c
Normal file
@@ -0,0 +1,172 @@
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/*-------------------------------------------------------------------------
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* snapmgmt.c
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* PostgreSQL snapshot management code.
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*
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* Portions Copyright (c) 1996-2008, 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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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/utils/time/snapmgmt.c,v 1.1 2008/03/26 16:20:47 alvherre Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/xact.h"
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#include "access/transam.h"
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#include "storage/procarray.h"
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#include "utils/snapmgmt.h"
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#include "utils/tqual.h"
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/*
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* These SnapshotData structs are static to simplify memory allocation
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* (see the hack in GetSnapshotData to avoid repeated malloc/free).
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*/
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static SnapshotData SerializableSnapshotData = {HeapTupleSatisfiesMVCC};
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static SnapshotData LatestSnapshotData = {HeapTupleSatisfiesMVCC};
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/* Externally visible pointers to valid snapshots: */
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Snapshot SerializableSnapshot = NULL;
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Snapshot LatestSnapshot = NULL;
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/*
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* This pointer is not maintained by this module, but it's convenient
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* to declare it here anyway. Callers typically assign a copy of
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* GetTransactionSnapshot's result to ActiveSnapshot.
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*/
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Snapshot ActiveSnapshot = NULL;
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/*
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* These are updated by GetSnapshotData. We initialize them this way
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* for the convenience of TransactionIdIsInProgress: even in bootstrap
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* mode, we don't want it to say that BootstrapTransactionId is in progress.
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*/
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TransactionId TransactionXmin = FirstNormalTransactionId;
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TransactionId RecentXmin = FirstNormalTransactionId;
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TransactionId RecentGlobalXmin = FirstNormalTransactionId;
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/*
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* GetTransactionSnapshot
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* Get the appropriate snapshot for a new query in a transaction.
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*
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* The SerializableSnapshot is the first one taken in a transaction.
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* In serializable mode we just use that one throughout the transaction.
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* In read-committed mode, we take a new snapshot each time we are called.
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*
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* Note that the return value points at static storage that will be modified
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* by future calls and by CommandCounterIncrement(). Callers should copy
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* the result with CopySnapshot() if it is to be used very long.
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*/
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Snapshot
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GetTransactionSnapshot(void)
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{
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/* First call in transaction? */
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if (SerializableSnapshot == NULL)
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{
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SerializableSnapshot = GetSnapshotData(&SerializableSnapshotData, true);
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return SerializableSnapshot;
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}
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if (IsXactIsoLevelSerializable)
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return SerializableSnapshot;
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LatestSnapshot = GetSnapshotData(&LatestSnapshotData, false);
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return LatestSnapshot;
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}
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/*
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* GetLatestSnapshot
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* Get a snapshot that is up-to-date as of the current instant,
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* even if we are executing in SERIALIZABLE mode.
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*/
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Snapshot
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GetLatestSnapshot(void)
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{
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/* Should not be first call in transaction */
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if (SerializableSnapshot == NULL)
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elog(ERROR, "no snapshot has been set");
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LatestSnapshot = GetSnapshotData(&LatestSnapshotData, false);
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return LatestSnapshot;
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}
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/*
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* CopySnapshot
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* Copy the given snapshot.
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*
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* The copy is palloc'd in the current memory context.
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*/
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Snapshot
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CopySnapshot(Snapshot snapshot)
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{
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Snapshot newsnap;
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Size subxipoff;
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Size size;
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/* We allocate any XID arrays needed in the same palloc block. */
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size = subxipoff = sizeof(SnapshotData) +
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snapshot->xcnt * sizeof(TransactionId);
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if (snapshot->subxcnt > 0)
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size += snapshot->subxcnt * sizeof(TransactionId);
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newsnap = (Snapshot) palloc(size);
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memcpy(newsnap, snapshot, sizeof(SnapshotData));
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/* setup XID array */
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if (snapshot->xcnt > 0)
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{
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newsnap->xip = (TransactionId *) (newsnap + 1);
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memcpy(newsnap->xip, snapshot->xip,
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snapshot->xcnt * sizeof(TransactionId));
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}
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else
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newsnap->xip = NULL;
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/* setup subXID array */
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if (snapshot->subxcnt > 0)
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{
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newsnap->subxip = (TransactionId *) ((char *) newsnap + subxipoff);
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memcpy(newsnap->subxip, snapshot->subxip,
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snapshot->subxcnt * sizeof(TransactionId));
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}
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else
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newsnap->subxip = NULL;
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return newsnap;
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}
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/*
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* FreeSnapshot
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* Free a snapshot previously copied with CopySnapshot.
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*
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* This is currently identical to pfree, but is provided for cleanliness.
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*
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* Do *not* apply this to the results of GetTransactionSnapshot or
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* GetLatestSnapshot, since those are just static structs.
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*/
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void
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FreeSnapshot(Snapshot snapshot)
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{
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pfree(snapshot);
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}
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/*
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* FreeXactSnapshot
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* Free snapshot(s) at end of transaction.
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*/
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void
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FreeXactSnapshot(void)
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{
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/*
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* We do not free the xip arrays for the static snapshot structs; they
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* will be reused soon. So this is now just a state change to prevent
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* outside callers from accessing the snapshots.
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*/
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SerializableSnapshot = NULL;
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LatestSnapshot = NULL;
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ActiveSnapshot = NULL; /* just for cleanliness */
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}
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@@ -31,7 +31,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.109 2008/01/01 19:45:55 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.110 2008/03/26 16:20:47 alvherre Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@@ -53,33 +53,6 @@ SnapshotData SnapshotSelfData = {HeapTupleSatisfiesSelf};
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SnapshotData SnapshotAnyData = {HeapTupleSatisfiesAny};
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SnapshotData SnapshotToastData = {HeapTupleSatisfiesToast};
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/*
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* These SnapshotData structs are static to simplify memory allocation
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* (see the hack in GetSnapshotData to avoid repeated malloc/free).
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*/
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static SnapshotData SerializableSnapshotData = {HeapTupleSatisfiesMVCC};
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static SnapshotData LatestSnapshotData = {HeapTupleSatisfiesMVCC};
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/* Externally visible pointers to valid snapshots: */
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Snapshot SerializableSnapshot = NULL;
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Snapshot LatestSnapshot = NULL;
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/*
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* This pointer is not maintained by this module, but it's convenient
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* to declare it here anyway. Callers typically assign a copy of
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* GetTransactionSnapshot's result to ActiveSnapshot.
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*/
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Snapshot ActiveSnapshot = NULL;
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/*
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* These are updated by GetSnapshotData. We initialize them this way
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* for the convenience of TransactionIdIsInProgress: even in bootstrap
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* mode, we don't want it to say that BootstrapTransactionId is in progress.
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*/
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TransactionId TransactionXmin = FirstNormalTransactionId;
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TransactionId RecentXmin = FirstNormalTransactionId;
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TransactionId RecentGlobalXmin = FirstNormalTransactionId;
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/* local functions */
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static bool XidInMVCCSnapshot(TransactionId xid, Snapshot snapshot);
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@@ -1235,130 +1208,6 @@ HeapTupleSatisfiesVacuum(HeapTupleHeader tuple, TransactionId OldestXmin,
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}
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/*
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* GetTransactionSnapshot
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* Get the appropriate snapshot for a new query in a transaction.
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*
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* The SerializableSnapshot is the first one taken in a transaction.
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* In serializable mode we just use that one throughout the transaction.
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* In read-committed mode, we take a new snapshot each time we are called.
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*
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* Note that the return value points at static storage that will be modified
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* by future calls and by CommandCounterIncrement(). Callers should copy
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* the result with CopySnapshot() if it is to be used very long.
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*/
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Snapshot
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GetTransactionSnapshot(void)
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{
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/* First call in transaction? */
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if (SerializableSnapshot == NULL)
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{
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SerializableSnapshot = GetSnapshotData(&SerializableSnapshotData, true);
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return SerializableSnapshot;
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}
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if (IsXactIsoLevelSerializable)
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return SerializableSnapshot;
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LatestSnapshot = GetSnapshotData(&LatestSnapshotData, false);
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return LatestSnapshot;
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}
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/*
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* GetLatestSnapshot
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* Get a snapshot that is up-to-date as of the current instant,
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* even if we are executing in SERIALIZABLE mode.
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*/
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Snapshot
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GetLatestSnapshot(void)
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{
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/* Should not be first call in transaction */
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if (SerializableSnapshot == NULL)
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elog(ERROR, "no snapshot has been set");
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LatestSnapshot = GetSnapshotData(&LatestSnapshotData, false);
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return LatestSnapshot;
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}
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/*
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* CopySnapshot
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* Copy the given snapshot.
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*
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* The copy is palloc'd in the current memory context.
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*/
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Snapshot
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CopySnapshot(Snapshot snapshot)
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{
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Snapshot newsnap;
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Size subxipoff;
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Size size;
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/* We allocate any XID arrays needed in the same palloc block. */
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size = subxipoff = sizeof(SnapshotData) +
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snapshot->xcnt * sizeof(TransactionId);
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if (snapshot->subxcnt > 0)
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size += snapshot->subxcnt * sizeof(TransactionId);
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newsnap = (Snapshot) palloc(size);
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memcpy(newsnap, snapshot, sizeof(SnapshotData));
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/* setup XID array */
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if (snapshot->xcnt > 0)
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{
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newsnap->xip = (TransactionId *) (newsnap + 1);
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memcpy(newsnap->xip, snapshot->xip,
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snapshot->xcnt * sizeof(TransactionId));
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}
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else
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newsnap->xip = NULL;
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/* setup subXID array */
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if (snapshot->subxcnt > 0)
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{
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newsnap->subxip = (TransactionId *) ((char *) newsnap + subxipoff);
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memcpy(newsnap->subxip, snapshot->subxip,
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snapshot->subxcnt * sizeof(TransactionId));
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}
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else
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newsnap->subxip = NULL;
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return newsnap;
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}
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/*
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* FreeSnapshot
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* Free a snapshot previously copied with CopySnapshot.
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*
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* This is currently identical to pfree, but is provided for cleanliness.
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*
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* Do *not* apply this to the results of GetTransactionSnapshot or
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* GetLatestSnapshot, since those are just static structs.
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*/
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void
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FreeSnapshot(Snapshot snapshot)
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{
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pfree(snapshot);
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}
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/*
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* FreeXactSnapshot
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* Free snapshot(s) at end of transaction.
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*/
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void
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FreeXactSnapshot(void)
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{
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/*
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* We do not free the xip arrays for the static snapshot structs; they
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* will be reused soon. So this is now just a state change to prevent
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* outside callers from accessing the snapshots.
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*/
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SerializableSnapshot = NULL;
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LatestSnapshot = NULL;
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ActiveSnapshot = NULL; /* just for cleanliness */
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}
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/*
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* XidInMVCCSnapshot
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* Is the given XID still-in-progress according to the snapshot?
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