Allow read only connections during recovery, known as Hot Standby.

Enabled by recovery_connections = on (default) and forcing archive recovery using a recovery.conf. Recovery processing now emulates the original transactions as they are replayed, providing full locking and MVCC behaviour for read only queries. Recovery must enter consistent state before connections are allowed, so there is a delay, typically short, before connections succeed. Replay of recovering transactions can conflict and in some cases deadlock with queries during recovery; these result in query cancellation after max_standby_delay seconds have expired. Infrastructure changes have minor effects on normal running, though introduce four new types of WAL record.

New test mode "make standbycheck" allows regression tests of static command behaviour on a standby server while in recovery. Typical and extreme dynamic behaviours have been checked via code inspection and manual testing. Few port specific behaviours have been utilised, though primary testing has been on Linux only so far.

This commit is the basic patch. Additional changes will follow in this release to enhance some aspects of behaviour, notably improved handling of conflicts, deadlock detection and query cancellation. Changes to VACUUM FULL are also required.

Simon Riggs, with significant and lengthy review by Heikki Linnakangas, including streamlined redesign of snapshot creation and two-phase commit.

Important contributions from Florian Pflug, Mark Kirkwood, Merlin Moncure, Greg Stark, Gianni Ciolli, Gabriele Bartolini, Hannu Krosing, Robert Haas, Tatsuo Ishii, Hiroyuki Yamada plus support and feedback from many other community members.

1 files changed, 9 insertions, 23 deletions

diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index 46eca9c9834..b272e9886bb 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -42,7 +42,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/multixact.c,v 1.32 2009/11/23 09:58:36 heikki Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/multixact.c,v 1.33 2009/12/19 01:32:33 sriggs Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -59,6 +59,7 @@
 #include "storage/backendid.h"
 #include "storage/lmgr.h"
 #include "storage/procarray.h"
+#include "utils/builtins.h"
 #include "utils/memutils.h"
 
 
@@ -220,7 +221,6 @@ static MultiXactId GetNewMultiXactId(int nxids, MultiXactOffset *offset);
 static MultiXactId mXactCacheGetBySet(int nxids, TransactionId *xids);
 static int	mXactCacheGetById(MultiXactId multi, TransactionId **xids);
 static void mXactCachePut(MultiXactId multi, int nxids, TransactionId *xids);
-static int	xidComparator(const void *arg1, const void *arg2);
 
 #ifdef MULTIXACT_DEBUG
 static char *mxid_to_string(MultiXactId multi, int nxids, TransactionId *xids);
@@ -1221,27 +1221,6 @@ mXactCachePut(MultiXactId multi, int nxids, TransactionId *xids)
 	MXactCache = entry;
 }
 
-/*
- * xidComparator
- *		qsort comparison function for XIDs
- *
- * We don't need to use wraparound comparison for XIDs, and indeed must
- * not do so since that does not respect the triangle inequality!  Any
- * old sort order will do.
- */
-static int
-xidComparator(const void *arg1, const void *arg2)
-{
-	TransactionId xid1 = *(const TransactionId *) arg1;
-	TransactionId xid2 = *(const TransactionId *) arg2;
-
-	if (xid1 > xid2)
-		return 1;
-	if (xid1 < xid2)
-		return -1;
-	return 0;
-}
-
 #ifdef MULTIXACT_DEBUG
 static char *
 mxid_to_string(MultiXactId multi, int nxids, TransactionId *xids)
@@ -2051,11 +2030,18 @@ multixact_redo(XLogRecPtr lsn, XLogRecord *record)
 			if (TransactionIdPrecedes(max_xid, xids[i]))
 				max_xid = xids[i];
 		}
+
+		/* We don't expect anyone else to modify nextXid, hence startup process
+		 * doesn't need to hold a lock while checking this. We still acquire
+		 * the lock to modify it, though.
+		 */
 		if (TransactionIdFollowsOrEquals(max_xid,
 										 ShmemVariableCache->nextXid))
 		{
+			LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
 			ShmemVariableCache->nextXid = max_xid;
 			TransactionIdAdvance(ShmemVariableCache->nextXid);
+			LWLockRelease(XidGenLock);
 		}
 	}
 	else