Arrange to fsync two-phase-commit state files only during checkpoints;

given reasonably short lifespans for prepared transactions, this should
mean that only a small minority of state files ever need to be fsynced
at all.  Per discussion with Heikki Linnakangas.

src/backend/access/transam/xact.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.206 2005/06/18 19:33:41 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.207 2005/06/19 20:00:38 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1741,19 +1741,6 @@ PrepareTransaction(void)
 	 */
 	EndPrepare(gxact);
 
-	/*
-	 * Mark the prepared transaction as valid.  As soon as we mark ourselves
-	 * not running in MyProc below, others can commit/rollback the xact.
-	 *
-	 * NB: a side effect of this is to make a dummy ProcArray entry for the
-	 * prepared XID.  This must happen before we clear the XID from MyProc,
-	 * else there is a window where the XID is not running according to
-	 * TransactionIdInProgress, and onlookers would be entitled to assume
-	 * the xact crashed.  Instead we have a window where the same XID
-	 * appears twice in ProcArray, which is OK.
-	 */
-	MarkAsPrepared(gxact);
-
 	/*
 	 * Now we clean up backend-internal state and release internal
 	 * resources.

src/backend/access/transam/xlog.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.201 2005/06/17 22:32:43 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.202 2005/06/19 20:00:38 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -5110,6 +5110,8 @@ CreateCheckPoint(bool shutdown, bool force)
 	CheckPointSUBTRANS();
 	CheckPointMultiXact();
 	FlushBufferPool();
+	/* We deliberately delay 2PC checkpointing as long as possible */
+	CheckPointTwoPhase(checkPoint.redo);
 
 	START_CRIT_SECTION();
 

src/include/access/twophase.h

@@ -7,14 +7,14 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/twophase.h,v 1.2 2005/06/18 19:33:42 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/access/twophase.h,v 1.3 2005/06/19 20:00:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #ifndef TWOPHASE_H
 #define TWOPHASE_H
 
-#include "storage/lock.h"
+#include "storage/proc.h"
 #include "utils/timestamp.h"
 
 
@@ -35,7 +35,6 @@ extern PGPROC *TwoPhaseGetDummyProc(TransactionId xid);
 extern GlobalTransaction MarkAsPreparing(TransactionId xid, const char *gid,
 										 TimestampTz prepared_at,
 										 AclId owner, Oid databaseid);
-extern void MarkAsPrepared(GlobalTransaction gxact);
 
 extern void StartPrepare(GlobalTransaction gxact);
 extern void EndPrepare(GlobalTransaction gxact);
@@ -46,6 +45,8 @@ extern void RecoverPreparedTransactions(void);
 extern void RecreateTwoPhaseFile(TransactionId xid, void *content, int len);
 extern void RemoveTwoPhaseFile(TransactionId xid, bool giveWarning);
 
+extern void CheckPointTwoPhase(XLogRecPtr redo_horizon);
+
 extern void FinishPreparedTransaction(const char *gid, bool isCommit);
 
 #endif   /* TWOPHASE_H */