Subject: Re: Context switch storm
From: Andreas Kostyrka <andreas@kostyrka.org>
To: Richard Huxton <dev@archonet.com>
Cc: creimer@brturbo.com.br, pgsql-performance@postgresql.org
In-Reply-To: <454B5461.4030802@archonet.com>
References: <efc1d7c07cf.454afe8d@brturbo.com.br> <454B3B75.6@archonet.com>
	<c4069b084d04.454b27e4@brturbo.com.br> <454B5461.4030802@archonet.com>
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Date: Fri, 03 Nov 2006 17:16:31 +0100
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Am Freitag, den 03.11.2006, 14:38 +0000 schrieb Richard Huxton:
> creimer@brturbo.com.br wrote:
> >> If you can keep your numbers of clients down below the critical=20
> >> level, you should find the overall workload is fine.
> >=20
> > We have at about 600 connections. Is this a case to use a connection
> > pool (pg_pool) system?
>=20
> Possibly - that should help. I'm assuming that most of your queries are=20
> very short, so you could probably get that figure down a lot lower.=20
> You'll keep the same amount of queries running through the system, just=20
> queue them up.
that have=20
Ah, yes, now that you mention, avoid running many queries with a
similiar timing behaviour, PG8 seems to have a lock design that's very
bad for the memory architecture of the Xeons.

So running SELECT * FROM table WHERE id=3D1234567890; from 600 clients in
parallel can be quite bad than say a complicated 6-way join :(

Andreas

>=20
> > And why this happens only with 8.0 and 8.1 and not with the 7.4?
>=20
> Not sure. Maybe 8.x is making more intensive use of your memory,=20
> possibly with a change in your plans.
>=20

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