From 1a3d104475ce01326fc00601ed66ac4d658e37e5 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Fri, 22 Nov 2013 12:53:59 +0200
Subject: [PATCH] Avoid acquiring spinlock when checking if recovery has
finished, for speed.
RecoveryIsInProgress() can be called very frequently. During normal
operation, it just checks a backend-local variable and returns quickly,
but during hot standby, it checks a spinlock-protected shared variable.
Those spinlock acquisitions can become a point of contention on a busy
hot standby system.
Replace the spinlock acquisition with a memory barrier.
Per discussion with Andres Freund, Ants Aasma and Merlin Moncure.
---
src/backend/access/transam/xlog.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
mode change 100644 => 100755 src/backend/access/transam/xlog.c
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
old mode 100644
new mode 100755
index a95149b9399..de19d2240fc
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7367,13 +7367,13 @@ RecoveryInProgress(void)
return false;
else
{
- /* use volatile pointer to prevent code rearrangement */
+ /*
+ * use volatile pointer to make sure we make a fresh read of the
+ * shared variable.
+ */
volatile XLogCtlData *xlogctl = XLogCtl;
- /* spinlock is essential on machines with weak memory ordering! */
- SpinLockAcquire(&xlogctl->info_lck);
LocalRecoveryInProgress = xlogctl->SharedRecoveryInProgress;
- SpinLockRelease(&xlogctl->info_lck);
/*
* Initialize TimeLineID and RedoRecPtr when we discover that recovery
@@ -7382,7 +7382,20 @@ RecoveryInProgress(void)
* this, see also LocalSetXLogInsertAllowed.)
*/
if (!LocalRecoveryInProgress)
+ {
+ /*
+ * If we just exited recovery, make sure we read TimeLineID and
+ * RedoRecPtr after SharedRecoveryInProgress (for machines with
+ * weak memory ordering).
+ */
+ pg_memory_barrier();
InitXLOGAccess();
+ }
+ /*
+ * Note: We don't need a memory barrier when we're still in recovery.
+ * We might exit recovery immediately after return, so the caller
+ * can't rely on 'true' meaning that we're still in recovery anyway.
+ */
return LocalRecoveryInProgress;
}
--
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