From: Frank Wiles <frank@wiles.org>
To: Markus Schaber <schabi@logix-tt.com>
Cc: PostgreSQL Performance List <pgsql-performance@postgresql.org>
Subject: Re: PostgreSQL underestimates sorting
Date: Wed, 22 Nov 2006 10:53:41 -0600
Message-ID: <20061122105341.79874069.frank@wiles.org> (raw)
In-Reply-To: <45645E7C.4030101@logix-tt.com>
References: <456423B3.7010505@logix-tt.com>
<20061122135434.GA9669@uio.no>
<45645E7C.4030101@logix-tt.com>
On Wed, 22 Nov 2006 15:28:12 +0100
Markus Schaber <schabi@logix-tt.com> wrote:
> Hi, Steinar,
>
> Steinar H. Gunderson wrote:
> > On Wed, Nov 22, 2006 at 11:17:23AM +0100, Markus Schaber wrote:
> >> The Backend allocates gigs of memory (we've set sort_mem to 1
> >> gig), and then starts spilling out more Gigs of temporary data to
> >> the disk.
> >
> > How much RAM is in the server? Remember that sort_mem is _per
> > sort_, so if you have multiple sorts, it might allocate several
> > multiples of the amount you set up.
>
> That one machine has 16 Gigs of ram, and about 10 Gigs tend to be
> "free" / part of the Linux blocklayer cache.
>
> The temporary data is not swapping, it's the Postgres on-disk sort
> algorithm.
Are you actually running a query where you have a GB of data
you need to sort? If not I fear you may be causing the system
to swap by setting it this high.
---------------------------------
Frank Wiles <frank@wiles.org>
http://www.wiles.org
---------------------------------
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To: pgsql-performance@postgresql.org
Cc: frank@wiles.org, schabi@logix-tt.com
Subject: Re: PostgreSQL underestimates sorting
In-Reply-To: <20061122105341.79874069.frank@wiles.org>
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