Re: [COMMITTERS] pgsql: Make walsender more responsive.

On Mon, Jul 2, 2012 at 10:49 PM, Robert Haas <rhaas@postgresql.org> wrote:
> Make walsender more responsive.
>
> Per testing by Andres Freund, this improves replication performance
> and reduces replication latency and latency jitter.  I was a bit
> concerned about moving more work into XLogInsert, but testing seems
> to show that it's not a problem in practice.
>
> Along the way, improve comments for WaitLatchOrSocket.

This commit makes the synchronous replication slow down very much
when wal_sync_method is set to open_sync or open_datasync. I think
the attached patch needs to be applied.

+#define WalSndWakeupProcessRequests()		\
+	do										\
+	{										\
+		if (wake_wal_senders)				\
+		{									\
+			wake_wal_senders = false;		\
+			if (max_wal_senders > 0)		\
+				WalSndWakeup();				\
+		}									\
+	} while (0)

I'm not sure it's really worth doing, but isn't it good idea to test
max_wal_sender > 0 first to eliminate any CPU cycle in non replication case?

Regards,

-- 
Fujii Masao