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

On Mon, Jul 2, 2012 at 10:49 PM, Robert Haas <rhaas(at)postgresql(dot)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