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Message-ID: <45645E7C.4030101@logix-tt.com>
Date: Wed, 22 Nov 2006 15:28:12 +0100
From: Markus Schaber <schabi@logix-tt.com>
Organization: Logical Tracking and Tracing International AG, Switzerland
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To: Markus Schaber <schabi@logix-tt.com>,
	PostgreSQL Performance List <pgsql-performance@postgresql.org>
Subject: Re: PostgreSQL underestimates sorting
References: <456423B3.7010505@logix-tt.com> <20061122135434.GA9669@uio.no>
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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.

HTH,
Markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

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