Received: from localhost (unknown [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 6463D2E079B for ; Wed, 26 Dec 2007 14:24:12 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.184]) (amavisd-maia, port 10024) with ESMTP id 46353-04 for ; Wed, 26 Dec 2007 14:24:00 -0400 (AST) Received: from westnet.com (westnet.com [216.187.52.2]) by postgresql.org (Postfix) with ESMTP id 8BCC42E033C for ; Wed, 26 Dec 2007 14:24:01 -0400 (AST) Received: from westnet.com (localhost [127.0.0.1]) by westnet.com (8.14.0/8.14.0) with ESMTP id lBQINwfX017256; Wed, 26 Dec 2007 13:23:58 -0500 (EST) Received: from localhost (gsmith@localhost) by westnet.com (8.14.0/8.13.2/Submit) with ESMTP id lBQINwHn017250; Wed, 26 Dec 2007 13:23:58 -0500 (EST) X-Authentication-Warning: westnet.com: gsmith owned process doing -bs Date: Wed, 26 Dec 2007 13:23:58 -0500 (EST) From: Greg Smith X-X-Sender: gsmith@westnet.com To: Guillaume Smet cc: pgsql-performance Subject: Re: More shared buffers causes lower performances In-Reply-To: <1d4e0c10712260741w1f141fd6x2f482143d526ad48@mail.gmail.com> Message-ID: References: <1d4e0c10712251606q6f9503deye3da4b68c51bf5e@mail.gmail.com> <1198668065.4221.288.camel@ebony.site> <1d4e0c10712260741w1f141fd6x2f482143d526ad48@mail.gmail.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200712/365 X-Sequence-Number: 28181 On Wed, 26 Dec 2007, Guillaume Smet wrote: > It's not checkpointing either as using pgbench-tools, I can see that > tps and latency are quite stable during the entire run. Btw, thanks > Greg for these nice tools. I stole the graph idea from Mark Wong's DBT2 code and one of these days I'll credit him appropriately. > Then I decided to perform read-only tests using -S option (pgbench -S > -s 100 -c 16 -t 30000 -U postgres bench). And still the same > behaviour: > shared_buffers=64MB : 20k tps > shared_buffers=1024MB : 8k tps Ah, now this is really interesting, as it rules out all the write components and should be easy to replicate even on a smaller server. As you've already dumped a bunch of time into this the only other thing I would suggest checking is whether the same behavior also happens on 8.2 on your server. -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD