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have been replaced by FrozenTransactionId.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.

1 files changed, 1 insertions, 31 deletions

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 $
  *
  *-------------------------------------------------------------------------
  */
@@ -5344,36 +5344,6 @@ GetLastSegSwitchTime(void)
 }
 
 /*
- * 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
  *
  * This is exported for use by code that would like to have 64-bit XIDs.