Re: hot_standby_feedback doesn't work on busy servers in 9.3+

On 2014-01-17 10:50:29 +0200, Heikki Linnakangas wrote:
> On 01/16/2014 11:55 PM, Andres Freund wrote:
> >On 2014-01-16 23:24:13 +0200, Heikki Linnakangas wrote:
> >>The reply message contains a pointers for how far the WAL has been applied,
> >>written, and flushed. There can be a significant delay between the write and
> >>flush steps, so we send a separate reply after writing, and after flushing.
> >>(if we didn't, the flush and write pointers sent to the master would always
> >>be the equal).
> >
> >If we'd always send a message, I'd be convinced by that argument, but
> >we're only sending messages after a timeout. This means that if syncrep
> >is on, we will more frequently have explicitly ask the receiver to send
> >a confirmation since the reply before the flush will have reset the
> >timers causing the reply after the flush to only infrequently send
> >something.
>
> No, XLogWalRcvSendReply also sends the reply if the flush or write pointers
> have advanced since last reply, even if the timeout hasn't expired.

Uh. Yes. I mis-remembered that we weren't doing that, but that's just
the apply value...

Sorry for the noise,
'
Andres Freund

--
 Andres Freund                       http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services