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Re: Removal of WAL logs

From: Josh Kupershmidt <schmiddy(at)gmail(dot)com>
To: "Birchall, Austen" <austen(dot)birchall(at)metoffice(dot)gov(dot)uk>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: Removal of WAL logs
Date: 2012-01-06 04:47:44
Message-ID: CAK3UJRFs92b=Uky7_k7cH0DAfkDKL1HBjzT==pkeRzxhqCqcSA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-novice
On Wed, Jan 4, 2012 at 7:00 AM, Birchall, Austen
<austen(dot)birchall(at)metoffice(dot)gov(dot)uk> wrote:
> Hi List
>
> I'm on 8.4.5 in WAL mode

What do you mean by "WAL mode"?

> with a database that has a low transaction rate and
> will probably be running nightly backups.
>
> Is there a recommendation for how many WAL logs I should keep on disk in
> pg_xlog and also how many to keep on external tape?

For a master server (ignoring backup aspects for the moment), the main
reason to allow more WAL files to accumulate in ./pg_xlog/ is to get
some throughput increase, particularly during bulk data loads. See:
  http://www.postgresql.org/docs/current/static/wal-configuration.html

specifically the paragraph beginning "There will always be at least
one WAL segment file...".

I'm not sure what you mean by "keep on external tape" bit -- are you
using a cold/warm standby, or otherwise archiving your WAL files to
tape?

> Are there any simple scripts/procedures that will mange the WAL logs and in
> particular delete them from pg_xlog when they are no longer needed so that
> they don't fill up the disk?

Your server should be recycling WAL files. You should never be
deleting these files by hand. (For a standby server, you may need to
be cleaning out copied WAL files once your standby has digested them,
but that's a separate topic -- look up pg_archivecleanup). If you are
seeing old WAL files build up in your ./pg_xlog/ directory, that might
indicate some problem. Check your postmaster log file, especially for
some problem with archive_command which might cause old files to be
kept.


Josh

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