Re: [Again] Postgres performance problem

From: "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com>
To: "Frank Schoep" <frank(at)ffnn(dot)nl>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: [Again] Postgres performance problem
Date: 2007-09-12 19:27:14
Message-ID: dcc563d10709121227j523937d9v3e6cf7fe8b5236d8@mail.gmail.com
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On 9/12/07, Frank Schoep <frank(at)ffnn(dot)nl> wrote:
> On Sep 12, 2007, at 9:07 PM, Scott Marlowe wrote:
> > On 9/12/07, Mikko Partio <mpartio(at)gmail(dot)com> wrote:
> >> …
> >> Aren't you mixing up REINDEX and CLUSTER?
> >
> > …
> > Either one does what a vacuum full did / does, but generally does
> > it better.
>
> On topic of REINDEX / VACUUM FULL versus a CLUSTER / VACUUM ANALYZE
> I'd like to ask if CLUSTER is safe to run on a table that is in
> active use.
>
> After updating my maintenance scripts from a VACUUM FULL (add me to
> the list) to CLUSTER (which improves performance a lot) I noticed I
> was getting "could not open relation …" errors in the log while the
> scripts ran so I reverted the change. This was on 8.1.9.
>
> Am I hitting a corner case or is it generally not a good idea to
> CLUSTER tables which are being queried? I haven't had problems with
> the REINDEX / VACUUM FULL combination while CLUSTER / VACUUM ANALYZE
> resulted in errors on the first run.
>
> Can the "could not open relation…" error bring down the whole
> database server? I'm really interested in using CLUSTER regularly as
> it speeds up my system by a factor of two because of more efficient I/O.

No, it won't bring it down. Basically the query lost the relation is
was operating against because it disappeared when the cluster command
runs.

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