From: Simon Riggs <simon@2ndQuadrant.com>
Date: Mon, 5 Oct 2009 14:13:37 +0000 (+0100)
Subject: Apply 0014-Make-locking-of-ShmemVariableCache-nextXid-in-multix.patch
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=48337207244784924fb4408f66fd15207b63dde8;p=users%2Fsimon%2Fpostgres.git

Apply 0014-Make-locking-of-ShmemVariableCache-nextXid-in-multix.patch
---

diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index 6f86961b88..80affa9624 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -1927,11 +1927,18 @@ 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 we
+		 * don'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