From: Jim C. Nasby <jim@nasby.net>
To: Merlin Moncure <mmoncure@gmail.com>
Cc: Cosimo Streppone <cosimo@streppone.it>
Cc: Richard Huxton <dev@archonet.com>
Cc: Postgresql Performance list <pgsql-performance@postgresql.org>
Subject: Re: Context switch storm
Date: Tue, 14 Nov 2006 10:50:22 -0600
Message-ID: <20061114165022.GS90133@nasby.net> (raw)
In-Reply-To: <b42b73150611140617m446e801bj7ec834bc661c138a@mail.gmail.com>
References: <efc1d7c07cf.454afe8d@brturbo.com.br>
<454B3B75.6@archonet.com>
<454B3EDC.3090502@streppone.it>
<454B4438.9080105@archonet.com>
<455991B0.6070209@streppone.it>
<b42b73150611140617m446e801bj7ec834bc661c138a@mail.gmail.com>
On Tue, Nov 14, 2006 at 09:17:08AM -0500, Merlin Moncure wrote:
> On 11/14/06, Cosimo Streppone <cosimo@streppone.it> wrote:
> >I must say I lowered "shared_buffers" to 8192, as it was before.
> >I tried raising it to 16384, but I can't seem to find a relationship
> >between shared_buffers and performance level for this server.
>
> My findings are pretty much the same here. I don't see any link
> between shared buffers and performance. I'm still looking for hard
> evidence to rebut this point. Lower shared buffers leaves more
> memory for what really matters, which is sorting.
It depends on your workload. If you're really sort-heavy, then having
memory available for that will be hard to beat. Otherwise, having a
large shared_buffers setting can really help cut down on switching back
and forth between the kernel and PostgreSQL.
BTW, shared_buffers of 16384 is pretty low by today's standards, so that
could be why you're not seeing much difference between that and 8192.
Try upping it to 1/4 - 1/2 of memory and see if that changes things.
--
Jim Nasby jim@nasby.net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: jim@nasby.net, mmoncure@gmail.com, cosimo@streppone.it, dev@archonet.com
Subject: Re: Context switch storm
In-Reply-To: <20061114165022.GS90133@nasby.net>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox