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Fix recently-understood problems with handling of XID freezing, particularly

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in PITR scenarios.  We now WAL-log the replacement of old XIDs with
FrozenTransactionId, so that such replacement is guaranteed to propagate to
PITR slave databases.  Also, rather than relying on hint-bit updates to be
preserved, pg_clog is not truncated until all instances of an XID are known to
have been replaced by FrozenTransactionId.  Add new GUC variables and
pg_autovacuum columns to allow management of the freezing policy, so that
users can trade off the size of pg_clog against the amount of freezing work
done.  Revise the already-existing code that forces autovacuum of tables
approaching the wraparound point to make it more bulletproof; also, revise the
autovacuum logic so that anti-wraparound vacuuming is done per-table rather
than per-database.  initdb forced because of changes in pg_class, pg_database,
and pg_autovacuum catalogs.  Heikki Linnakangas, Simon Riggs, and Tom Lane.
This commit is contained in:
Tom Lane
2006-11-05 22:42:10 +00:00
parent 10c70b8602
commit 48188e1621
43 changed files with 1284 additions and 1062 deletions
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32
src/backend/access/transam/xlog.c
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.252 2006/10/18 22:44:11 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.253 2006/11/05 22:42:08 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -5343,36 +5343,6 @@ GetLastSegSwitchTime(void)
return result;
}
/*
* GetRecentNextXid - get the nextXid value saved by the most recent checkpoint
*
* This is currently used only by the autovacuum daemon. To check for
* impending XID wraparound, autovac needs an approximate idea of the current
* XID counter, and it needs it before choosing which DB to attach to, hence
* before it sets up a PGPROC, hence before it can take any LWLocks. But it
* has attached to shared memory, and so we can let it reach into the shared
* ControlFile structure and pull out the last checkpoint nextXID.
*
* Since we don't take any sort of lock, we have to assume that reading a
* TransactionId is atomic ... but that assumption is made elsewhere, too,
* and in any case the worst possible consequence of a bogus result is that
* autovac issues an unnecessary database-wide VACUUM.
*
* Note: we could also choose to read ShmemVariableCache->nextXid in an
* unlocked fashion, thus getting a more up-to-date result; but since that
* changes far more frequently than the controlfile checkpoint copy, it would
* pose a far higher risk of bogus result if we did have a nonatomic-read
* problem.
*
* A (theoretically) completely safe answer is to read the actual pg_control
* file into local process memory, but that certainly seems like overkill.
*/
TransactionId
GetRecentNextXid(void)
{
return ControlFile->checkPointCopy.nextXid;
}
/*
* GetNextXidAndEpoch - get the current nextXid value and associated epoch
*