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

On Monday, July 02, 2012 07:19:19 PM Fujii Masao wrote:
> 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.
Hm. Yes, definitely. No idea why I placed the call there, sorry.

Thats how synchronous_write=off behaved generally till the recent (simple) fix
btw ;)

> +#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?
I think the difference is ignorable. wake_wal_senders probably has better
cache locality but is set to true more often, but not that often...

Thanks,

Andres
--
Andres Freund http://www.2ndQuadrant.com/
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