From: Decibel! <decibel@decibel.org>
To: Erik Jones <erik@myemma.com>
Cc: Frank Schoep <frank@ffnn.nl>
Cc: pgsql-performance@postgresql.org
Subject: Re: [Again] Postgres performance problem
Date: Mon, 17 Sep 2007 07:24:14 -0500
Message-ID: <20070917122414.GJ16759@decibel.org> (raw)
In-Reply-To: <2752E5D2-6FA0-4416-8FF4-4CE20573F67A@myemma.com>
References: <46E636CB.8080008@rentalia.com>
<43393.192.121.104.48.1189495883.squirrel@zigo.dhs.org>
<46E64891.9080005@rentalia.com>
<20070911225242.GG38801@decibel.org>
<46E79865.906@rentalia.com>
<dcc563d10709121128o1e5883a9n96b1f9ed74901be9@mail.gmail.com>
<2ca799770709121156l7ddbb20agf8086e8bfcbc881a@mail.gmail.com>
<dcc563d10709121207q66f09c33ldcd181e4a2876904@mail.gmail.com>
<A9ADD88B-83D8-43FC-A58F-A7D2D38B9311@ffnn.nl>
<2752E5D2-6FA0-4416-8FF4-4CE20573F67A@myemma.com>
On Wed, Sep 12, 2007 at 03:01:12PM -0500, Erik Jones wrote:
>
> On Sep 12, 2007, at 2:19 PM, Frank Schoep wrote:
>
> >On Sep 12, 2007, at 9:07 PM, Scott Marlowe wrote:
> >>On 9/12/07, Mikko Partio <mpartio@gmail.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.
>
> You'd probably see the same behavior on 8.2.x. CLUSTER is not
> transactionally safe so you don't want to run CLUSTER on tables that
> are actively being used. I believe that's been fixed for 8.3.
Actually, that's a bit over-conservative... what happens prior to 8.3 is
that CLUSTER rewrites the table using it's XID for everything. That can
break semantics for any transactions that are running in serializable
mode; if you're just using the default isolation level of read
committed, you're fine with CLUSTER.
--
Decibel!, aka Jim C. Nasby, Database Architect decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828
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To: pgsql-performance@postgresql.org
Cc: decibel@decibel.org, erik@myemma.com, frank@ffnn.nl
Subject: Re: [Again] Postgres performance problem
In-Reply-To: <20070917122414.GJ16759@decibel.org>
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