Re: PostgreSQL underestimates sorting

On Wed, 22 Nov 2006 15:28:12 +0100
Markus Schaber <schabi(at)logix-tt(dot)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(at)wiles(dot)org>
http://www.wiles.org
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