btree page recycling can be done as soon as page's next-xact label is

older than current Xmin; we don't have to wait till it's older than
GlobalXmin.

Author: tglsfdc

src/backend/access/nbtree/nbtpage.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtpage.c,v 1.62 2003/02/23 22:43:08 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtpage.c,v 1.63 2003/02/23 23:20:52 tgl Exp $
  *
  *	NOTES
  *	   Postgres btree pages look like ordinary relation pages.	The opaque
@@ -544,7 +544,7 @@ _bt_page_recyclable(Page page)
 	 */
 	opaque = (BTPageOpaque) PageGetSpecialPointer(page);
 	if (P_ISDELETED(opaque) &&
-		TransactionIdPrecedesOrEquals(opaque->btpo.xact, RecentGlobalXmin))
+		TransactionIdPrecedesOrEquals(opaque->btpo.xact, RecentXmin))
 		return true;
 	return false;
 }

src/backend/storage/ipc/sinval.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.53 2002/11/21 06:36:08 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.54 2003/02/23 23:20:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -298,9 +298,10 @@ GetOldestXmin(bool allDbs)
  * This ensures that the set of transactions seen as "running" by the
  * current xact will not change after it takes the snapshot.
  *
- * Also, we compute the current global xmin (oldest xmin across all running
+ * We also compute the current global xmin (oldest xmin across all running
  * transactions) and save it in RecentGlobalXmin.  This is the same
- * computation done by GetOldestXmin(TRUE).
+ * computation done by GetOldestXmin(TRUE).  The xmin value is also stored
+ * into RecentXmin.
  *----------
  */
 Snapshot
@@ -419,7 +420,9 @@ GetSnapshotData(bool serializable)
 	if (TransactionIdPrecedes(xmin, globalxmin))
 		globalxmin = xmin;
 
+	/* Update globals for use by VACUUM */
 	RecentGlobalXmin = globalxmin;
+	RecentXmin = xmin;
 
 	snapshot->xmin = xmin;
 	snapshot->xmax = xmax;

src/backend/utils/time/tqual.c

@@ -16,7 +16,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/time/tqual.c,v 1.61 2002/10/08 17:17:19 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/time/tqual.c,v 1.62 2003/02/23 23:20:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -33,7 +33,8 @@ Snapshot	SnapshotDirty = &SnapshotDirtyData;
 Snapshot	QuerySnapshot = NULL;
 Snapshot	SerializableSnapshot = NULL;
 
-/* This is updated by GetSnapshotData: */
+/* These are updated by GetSnapshotData: */
+TransactionId RecentXmin = InvalidTransactionId;
 TransactionId RecentGlobalXmin = InvalidTransactionId;
 
 bool		ReferentialIntegritySnapshotOverride = false;

src/include/utils/tqual.h

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: tqual.h,v 1.43 2002/09/04 20:31:46 momjian Exp $
+ * $Id: tqual.h,v 1.44 2003/02/23 23:20:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,6 +41,7 @@ extern DLLIMPORT Snapshot SnapshotDirty;
 extern DLLIMPORT Snapshot QuerySnapshot;
 extern DLLIMPORT Snapshot SerializableSnapshot;
 
+extern TransactionId RecentXmin;
 extern TransactionId RecentGlobalXmin;
 
 extern bool ReferentialIntegritySnapshotOverride;