From 48188e1621bb6711e7d092bee48523b18cd80177 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sun, 5 Nov 2006 22:42:10 +0000 Subject: Fix recently-understood problems with handling of XID freezing, particularly 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relying on hint-bit updates to be preserved, pg_clog is not truncated until all instances of an XID are known to have been replaced by FrozenTransactionId.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. --- src/backend/access/transam/xlog.c | 32 +------------------------------- 1 file changed, 1 insertion(+), 31 deletions(-) (limited to 'src/backend/access/transam/xlog.c') diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index ba029397f87..03440cbf48b 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -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 * -- cgit v1.2.3