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