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Improve snapshot manager by keeping explicit track of snapshots.

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There are two ways to track a snapshot: there's the "registered" list, which
is used for arbitrary long-lived snapshots; and there's the "active stack",
which is used for the snapshot that is considered "active" at any time.
This also allows users of snapshots to stop worrying about snapshot memory
allocation and freeing, and about using PG_TRY blocks around ActiveSnapshot
assignment.  This is all done automatically now.

As a consequence, this allows us to reset MyProc->xmin when there are no
more snapshots registered in the current backend, reducing the impact that
long-running transactions have on VACUUM.
This commit is contained in:
Alvaro Herrera
2008-05-12 20:02:02 +00:00
parent aa82790fca
commit 5da9da71c4
27 changed files with 995 additions and 551 deletions
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23
src/include/utils/snapmgr.h
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@@ -6,7 +6,7 @@
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/utils/snapmgr.h,v 1.1 2008/03/26 18:48:59 alvherre Exp $
* $PostgreSQL: pgsql/src/include/utils/snapmgr.h,v 1.2 2008/05/12 20:02:02 alvherre Exp $
*
*-------------------------------------------------------------------------
*/
@@ -16,9 +16,7 @@
#include "utils/snapshot.h"
extern PGDLLIMPORT Snapshot SerializableSnapshot;
extern PGDLLIMPORT Snapshot LatestSnapshot;
extern PGDLLIMPORT Snapshot ActiveSnapshot;
extern bool FirstSnapshotSet;
extern TransactionId TransactionXmin;
extern TransactionId RecentXmin;
@@ -26,8 +24,19 @@ extern TransactionId RecentGlobalXmin;
extern Snapshot GetTransactionSnapshot(void);
extern Snapshot GetLatestSnapshot(void);
extern Snapshot CopySnapshot(Snapshot snapshot);
extern void FreeSnapshot(Snapshot snapshot);
extern void FreeXactSnapshot(void);
extern void SnapshotSetCommandId(CommandId curcid);
extern void PushActiveSnapshot(Snapshot snapshot);
extern void PushUpdatedSnapshot(Snapshot snapshot);
extern void PopActiveSnapshot(void);
extern Snapshot GetActiveSnapshot(void);
extern bool ActiveSnapshotSet(void);
extern Snapshot RegisterSnapshot(Snapshot snapshot);
extern void UnregisterSnapshot(Snapshot snapshot);
extern void AtSubCommit_Snapshot(int level);
extern void AtSubAbort_Snapshot(int level);
extern void AtEOXact_Snapshot(bool isCommit);
#endif /* SNAPMGR_H */