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.)

diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index b8715ea6762ab85983f5a6dc88c09c89a9aa9979..a516856226fc09e18b1ea5d61461dd1f61a564e5 100644 (file)
--- 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;
        }