Improve vacuum code to track minimum Xids per table instead of per database.

To this end, add a couple of columns to pg_class, relminxid and relvacuumxid,
based on which we calculate the pg_database columns after each vacuum.

We now force all databases to be vacuumed, even template ones.  A backend
noticing too old a database (meaning pg_database.datminxid is in danger of
falling behind Xid wraparound) will signal the postmaster, which in turn will
start an autovacuum iteration to process the offending database.  In principle
this is only there to cope with frozen (non-connectable) databases without
forcing users to set them to connectable, but it could force regular user
database to go through a database-wide vacuum at any time.  Maybe we should
warn users about this somehow.  Of course the real solution will be to use
autovacuum all the time ;-)

There are some additional improvements we could have in this area: for example
the vacuum code could be smarter about not updating pg_database for each table
when called by autovacuum, and do it only once the whole autovacuum iteration
is done.

I updated the system catalogs documentation, but I didn't modify the
maintenance section.  Also having some regression tests for this would be nice
but it's not really a very straightforward thing to do.

Catalog version bumped due to system catalog changes.

1 files changed, 15 insertions, 15 deletions

diff --git a/src/backend/utils/init/flatfiles.c b/src/backend/utils/init/flatfiles.c
index 79e73af8201..4669fb9e9d4 100644
--- a/src/backend/utils/init/flatfiles.c
+++ b/src/backend/utils/init/flatfiles.c
@@ -23,7 +23,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/utils/init/flatfiles.c,v 1.18 2006/05/04 16:07:29 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/init/flatfiles.c,v 1.19 2006/07/10 16:20:51 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -163,7 +163,7 @@ name_okay(const char *str)
 /*
  * write_database_file: update the flat database file
  *
- * A side effect is to determine the oldest database's datfrozenxid
+ * A side effect is to determine the oldest database's datminxid
  * so we can set or update the XID wrap limit.
  */
 static void
@@ -177,7 +177,7 @@ write_database_file(Relation drel)
 	HeapScanDesc scan;
 	HeapTuple	tuple;
 	NameData	oldest_datname;
-	TransactionId oldest_datfrozenxid = InvalidTransactionId;
+	TransactionId oldest_datminxid = InvalidTransactionId;
 
 	/*
 	 * Create a temporary filename to be renamed later.  This prevents the
@@ -208,27 +208,27 @@ write_database_file(Relation drel)
 		char	   *datname;
 		Oid			datoid;
 		Oid			dattablespace;
-		TransactionId datfrozenxid,
+		TransactionId datminxid,
 					datvacuumxid;
 
 		datname = NameStr(dbform->datname);
 		datoid = HeapTupleGetOid(tuple);
 		dattablespace = dbform->dattablespace;
-		datfrozenxid = dbform->datfrozenxid;
+		datminxid = dbform->datminxid;
 		datvacuumxid = dbform->datvacuumxid;
 
 		/*
-		 * Identify the oldest datfrozenxid, ignoring databases that are not
+		 * Identify the oldest datminxid, ignoring databases that are not
 		 * connectable (we assume they are safely frozen).	This must match
 		 * the logic in vac_truncate_clog() in vacuum.c.
 		 */
 		if (dbform->datallowconn &&
-			TransactionIdIsNormal(datfrozenxid))
+			TransactionIdIsNormal(datminxid))
 		{
-			if (oldest_datfrozenxid == InvalidTransactionId ||
-				TransactionIdPrecedes(datfrozenxid, oldest_datfrozenxid))
+			if (oldest_datminxid == InvalidTransactionId ||
+				TransactionIdPrecedes(datminxid, oldest_datminxid))
 			{
-				oldest_datfrozenxid = datfrozenxid;
+				oldest_datminxid = datminxid;
 				namestrcpy(&oldest_datname, datname);
 			}
 		}
@@ -244,14 +244,14 @@ write_database_file(Relation drel)
 		}
 
 		/*
-		 * The file format is: "dbname" oid tablespace frozenxid vacuumxid
+		 * The file format is: "dbname" oid tablespace minxid vacuumxid
 		 *
 		 * The xids are not needed for backend startup, but are of use to
 		 * autovacuum, and might also be helpful for forensic purposes.
 		 */
 		fputs_quote(datname, fp);
 		fprintf(fp, " %u %u %u %u\n",
-				datoid, dattablespace, datfrozenxid, datvacuumxid);
+				datoid, dattablespace, datminxid, datvacuumxid);
 	}
 	heap_endscan(scan);
 
@@ -272,10 +272,10 @@ write_database_file(Relation drel)
 						tempname, filename)));
 
 	/*
-	 * Set the transaction ID wrap limit using the oldest datfrozenxid
+	 * Set the transaction ID wrap limit using the oldest datminxid
 	 */
-	if (oldest_datfrozenxid != InvalidTransactionId)
-		SetTransactionIdLimit(oldest_datfrozenxid, &oldest_datname);
+	if (oldest_datminxid != InvalidTransactionId)
+		SetTransactionIdLimit(oldest_datminxid, &oldest_datname);
 }