From 80e373c3a8c43812bdc98fe0d433b9990acce5ad Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 18 Jul 2012 15:40:31 -0400
Subject: [PATCH] Fix statistics breakage from bgwriter/checkpointer process
 split.

ForwardFsyncRequest() supposed that it could only be called in regular
backends, which used to be true; but since the splitup of bgwriter and
checkpointer, it is also called in the bgwriter.  We do not want to count
such calls in pg_stat_bgwriter.buffers_backend statistics, so fix things
so that they aren't.

(It's worth noting here that this implies an alarmingly large increase in
the expected amount of cross-process fsync request traffic, which may well
mean that the process splitup was not such a hot idea.)
---
 src/backend/postmaster/checkpointer.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index b8715ea676..a516856226 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -1132,7 +1132,8 @@ ForwardFsyncRequest(RelFileNode rnode, ForkNumber forknum, BlockNumber segno)
 	LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
 
 	/* Count all backend writes regardless of if they fit in the queue */
-	CheckpointerShmem->num_backend_writes++;
+	if (!AmBackgroundWriterProcess())
+		CheckpointerShmem->num_backend_writes++;
 
 	/*
 	 * If the checkpointer isn't running or the request queue is full, the
@@ -1147,7 +1148,8 @@ ForwardFsyncRequest(RelFileNode rnode, ForkNumber forknum, BlockNumber segno)
 		 * Count the subset of writes where backends have to do their own
 		 * fsync
 		 */
-		CheckpointerShmem->num_backend_fsync++;
+		if (!AmBackgroundWriterProcess())
+			CheckpointerShmem->num_backend_fsync++;
 		LWLockRelease(CheckpointerCommLock);
 		return false;
 	}
-- 
2.49.0