Track the current XID wrap limit (or more accurately, the oldest unfrozen

XID) in checkpoint records.  This eliminates the need to recompute the value
from scratch during database startup, which is one of the two remaining
reasons for the flatfile code to exist.  It should also simplify life for
hot-standby operation.

To avoid bloating the checkpoint records unreasonably, I switched from
tracking the oldest database by name to tracking it by OID.  This turns
out to save cycles in general (everywhere but the warning-generating
paths, which we hardly care about) and also helps us deal with the case
that the oldest database got dropped instead of being vacuumed.  The prior
coding might go for a long time without updating the wrap limit in that case,
which is bad because it might result in a lot of useless autovacuum activity.

1 files changed, 1 insertions, 26 deletions

diff --git a/src/backend/utils/init/flatfiles.c b/src/backend/utils/init/flatfiles.c
index fbbd372b141..38271653f6d 100644
--- a/src/backend/utils/init/flatfiles.c
+++ b/src/backend/utils/init/flatfiles.c
@@ -23,7 +23,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/utils/init/flatfiles.c,v 1.38 2009/08/29 19:26:51 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/init/flatfiles.c,v 1.39 2009/08/31 02:23:22 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -166,9 +166,6 @@ name_okay(const char *str)
 
 /*
  * write_database_file: update the flat database file
- *
- * A side effect is to determine the oldest database's datfrozenxid
- * so we can set or update the XID wrap limit.
  */
 static void
 write_database_file(Relation drel)
@@ -180,8 +177,6 @@ write_database_file(Relation drel)
 	mode_t		oumask;
 	HeapScanDesc scan;
 	HeapTuple	tuple;
-	NameData	oldest_datname;
-	TransactionId oldest_datfrozenxid = InvalidTransactionId;
 
 	/*
 	 * Create a temporary filename to be renamed later.  This prevents the
@@ -220,20 +215,6 @@ write_database_file(Relation drel)
 		datfrozenxid = dbform->datfrozenxid;
 
 		/*
-		 * Identify the oldest datfrozenxid.  This must match the logic in
-		 * vac_truncate_clog() in vacuum.c.
-		 */
-		if (TransactionIdIsNormal(datfrozenxid))
-		{
-			if (oldest_datfrozenxid == InvalidTransactionId ||
-				TransactionIdPrecedes(datfrozenxid, oldest_datfrozenxid))
-			{
-				oldest_datfrozenxid = datfrozenxid;
-				namestrcpy(&oldest_datname, datname);
-			}
-		}
-
-		/*
 		 * Check for illegal characters in the database name.
 		 */
 		if (!name_okay(datname))
@@ -270,12 +251,6 @@ write_database_file(Relation drel)
 				(errcode_for_file_access(),
 				 errmsg("could not rename file \"%s\" to \"%s\": %m",
 						tempname, filename)));
-
-	/*
-	 * Set the transaction ID wrap limit using the oldest datfrozenxid
-	 */
-	if (oldest_datfrozenxid != InvalidTransactionId)
-		SetTransactionIdLimit(oldest_datfrozenxid, &oldest_datname);
 }