From 17d8de0e6102d288a0745cb30499411c2e7ad213 Mon Sep 17 00:00:00 2001
From: Itagaki Takahiro <itagaki.takahiro@gmail.com>
Date: Wed, 10 Mar 2010 02:04:48 +0000
Subject: [PATCH] pg_start_backup() can use a share lock to lock
 ControlFileLock instead of an exclusive lock.

The change is almost for code cleanup. Since there seems to be no
performance benefits from it, backports should not be needed.

Fujii Masao
---
 src/backend/access/transam/xlog.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index d753a31cb3..55d1ea0549 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.379 2010/02/26 02:00:35 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.380 2010/03/10 02:04:48 itagaki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -7897,7 +7897,7 @@ pg_start_backup(PG_FUNCTION_ARGS)
 		 * REDO pointer.  The oldest point in WAL that would be needed to
 		 * restore starting from the checkpoint is precisely the REDO pointer.
 		 */
-		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+		LWLockAcquire(ControlFileLock, LW_SHARED);
 		checkpointloc = ControlFile->checkPoint;
 		startpoint = ControlFile->checkPointCopy.redo;
 		LWLockRelease(ControlFileLock);