Received: from localhost (mx1.hub.org [200.46.208.251]) by postgresql.org (Postfix) with ESMTP id 119D79FA618 for ; Tue, 14 Nov 2006 16:11:49 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.208.251]) (amavisd-new, port 10024) with ESMTP id 03528-10 for ; Tue, 14 Nov 2006 16:11:42 -0400 (AST) X-Greylist: domain auto-whitelisted by SQLgrey- Received: from ug-out-1314.google.com (ug-out-1314.google.com [66.249.92.169]) by postgresql.org (Postfix) with ESMTP id 4CBA99FA5C8 for ; Tue, 14 Nov 2006 16:11:42 -0400 (AST) Received: by ug-out-1314.google.com with SMTP id k3so1215851ugf for ; Tue, 14 Nov 2006 12:11:41 -0800 (PST) DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=eV9z/pZ/n9pcVeenwCkaBE7lJ9qX4hiGPc2NsayG+Qq9mjzr8mibCFqxxybs9VUkxr/ZTRcrqh1ycqFVr6sElCsZv4zvK0IkgF90dTucg2+Op24r7wVI8RektJfZ17HowaDlFOWolEZn6F1mU7b474dZPVbEano4HrDJuys+DEc= Received: by 10.78.97.7 with SMTP id u7mr1374768hub.1163535100542; Tue, 14 Nov 2006 12:11:40 -0800 (PST) Received: by 10.78.45.3 with HTTP; Tue, 14 Nov 2006 12:11:40 -0800 (PST) Message-ID: Date: Tue, 14 Nov 2006 15:11:40 -0500 From: "Merlin Moncure" To: "Jim C. Nasby" Subject: Re: Context switch storm Cc: "Cosimo Streppone" , "Richard Huxton" , "Postgresql Performance list" In-Reply-To: <20061114165022.GS90133@nasby.net> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <454B3B75.6@archonet.com> <454B3EDC.3090502@streppone.it> <454B4438.9080105@archonet.com> <455991B0.6070209@streppone.it> <20061114165022.GS90133@nasby.net> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200611/104 X-Sequence-Number: 21874 On 11/14/06, Jim C. Nasby wrote: > 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. Can you think of a good way to construct a test case that would demonstrate the difference? What would be the 'best case' where a high shared buffers would be favored over a low setting? merlin