Received: from localhost (wm.hub.org [200.46.204.128]) by postgresql.org (Postfix) with ESMTP id 21E859FB257 for ; Tue, 14 Nov 2006 12:50:39 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.128]) (amavisd-new, port 10024) with ESMTP id 09517-01 for ; Tue, 14 Nov 2006 16:50:29 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey- Received: from noel.decibel.org (noel.decibel.org [67.100.216.10]) by postgresql.org (Postfix) with ESMTP id D6A309FB251 for ; Tue, 14 Nov 2006 12:50:28 -0400 (AST) Received: by noel.decibel.org (Postfix, from userid 1001) id F37315643A; Tue, 14 Nov 2006 10:50:26 -0600 (CST) Received: (hashcash-sendmail, from uid 1001); Tue, 14 Nov 2006 10:50:22 -0600 Date: Tue, 14 Nov 2006 10:50:22 -0600 From: "Jim C. Nasby" To: Merlin Moncure Cc: Cosimo Streppone , Richard Huxton , Postgresql Performance list Subject: Re: Context switch storm Message-ID: <20061114165022.GS90133@nasby.net> References: <454B3B75.6@archonet.com> <454B3EDC.3090502@streppone.it> <454B4438.9080105@archonet.com> <455991B0.6070209@streppone.it> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: FreeBSD 6.1-RELEASE-p10 amd64 X-Distributed: Join the Effort! http://www.distributed.net User-Agent: Mutt/1.5.13 (2006-08-11) X-Hashcash: 1:20:061114:mmoncure@gmail.com::8loC1kGtNSvUnLOn:0000000000000000000 0000000000000000000000001pru X-Hashcash: 1:20:061114:cosimo@streppone.it::h5H5WZCAU8UJi78A:000000000000000000 00000000000000000000000009xd X-Hashcash: 1:20:061114:dev@archonet.com::BMRVEs9BACmmu1IK:02VnT X-Hashcash: 1:20:061114:pgsql-performance@postgresql.org::tmOaxGJmQgDvF0o+:00000 000000000000000000000000Cxdk X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200611/102 X-Sequence-Number: 21872 On Tue, Nov 14, 2006 at 09:17:08AM -0500, Merlin Moncure wrote: > On 11/14/06, Cosimo Streppone 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)