Re: Clean shutdown and warm standby

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andreas Pflug <pgadmin(at)pse-consulting(dot)de>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Clean shutdown and warm standby
Date: 2009-05-28 13:29:27
Message-ID: 1243517367.24860.553.camel@ebony.2ndQuadrant
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On Thu, 2009-05-28 at 16:19 +0300, Heikki Linnakangas wrote:
> Simon Riggs wrote:
> > On Thu, 2009-05-28 at 14:04 +0300, Heikki Linnakangas wrote:
> >
> >> I've committed a patch to do the RequstXLogSwitch() before shutdown
> >> checkpoint as discussed. It seems safe to me. (sorry for the delay, and
> >> thanks for the reminder)
> >
> > Not sure if that is a fix that will work in all cases.
> >
> > There is a potential timing problem with when the archiver is shutdown:
> > that may now be fixed in 8.4, see what you think.
>
> Can you elaborate?

Is the archiver still alive and working after the log switch occurs?

If the archiver is working, but has fallen behind at the point of
shutdown, does the archiver operate for long enough to ensure we are
archived up to the point of the log switch prior to checkpoint?

> > Also if archiving is currently stalled, then files will not be
> > transferred, even if you switch xlogs. So this is at best a partial fix
> > to the problem and the need for a manual check of file contents
> > remains.
>
> Yep. Maybe we should print the filename of the last WAL segment to the
> log at shutdown, so that you can easily check that you have everything
> in the archive.

You still need a script to read that and synchronize file contents.

--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support

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