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Ensure that a cursor has an immutable snapshot throughout its lifespan.

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The old coding was using a regular snapshot, referenced elsewhere, that was
subject to having its command counter updated.  Fix by creating a private copy
of the snapshot exclusively for the cursor.

Backpatch to 8.4, which is when the bug was introduced during the snapshot
management rewrite.
This commit is contained in:
Alvaro Herrera
2009-10-02 17:57:30 +00:00
parent fabf75cffc
commit caa4cfa369
6 changed files with 44 additions and 11 deletions
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5
src/backend/utils/time/snapmgr.c
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@ -19,7 +19,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/time/snapmgr.c,v 1.10 2009/06/11 14:49:06 momjian Exp $
* $PostgreSQL: pgsql/src/backend/utils/time/snapmgr.c,v 1.11 2009/10/02 17:57:30 alvherre Exp $
*
*-------------------------------------------------------------------------
*/
@ -104,7 +104,6 @@ bool FirstSnapshotSet = false;
static bool registered_serializable = false;
static Snapshot CopySnapshot(Snapshot snapshot);
static void FreeSnapshot(Snapshot snapshot);
static void SnapshotResetXmin(void);
@ -192,7 +191,7 @@ SnapshotSetCommandId(CommandId curcid)
* The copy is palloc'd in TopTransactionContext and has initial refcounts set
* to 0. The returned snapshot has the copied flag set.
*/
static Snapshot
Snapshot
CopySnapshot(Snapshot snapshot)
{
Snapshot newsnap;