Re: PostgreSQL underestimates sorting - Mailing list pgsql-performance

From Markus Schaber
Subject Re: PostgreSQL underestimates sorting
Date
Msg-id 45645E7C.4030101@logix-tt.com
Whole thread Raw
In response to Re: PostgreSQL underestimates sorting  ("Steinar H. Gunderson" <sgunderson@bigfoot.com>)
Responses Re: PostgreSQL underestimates sorting  (Frank Wiles <frank@wiles.org>)
List pgsql-performance
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

Fight against software patents in Europe! www.ffii.org
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