Received: from localhost (unknown [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id C3B962E316B for ; Thu, 29 Nov 2007 12:03:04 -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 05344-01-2 for ; Thu, 29 Nov 2007 12:02:46 -0400 (AST) Received: from main2.mycybernet.net (main2.mycybernet.net [209.222.63.140]) by postgresql.org (Postfix) with ESMTP id BD9722E3B8B for ; Thu, 29 Nov 2007 12:02:25 -0400 (AST) Received: from 227-54-222-209.mycybernet.net ([209.222.54.227] helo=crankycanuck.ca) by main2.mycybernet.net with esmtp (Exim 4.62) (envelope-from ) id 1IxlqL-0005KF-Ac for pgsql-performance@postgresql.org; Thu, 29 Nov 2007 11:02:25 -0500 Received: by crankycanuck.ca (Postfix, from userid 1000) id E04C850462; Thu, 29 Nov 2007 11:02:19 -0500 (EST) Date: Thu, 29 Nov 2007 11:02:19 -0500 From: Andrew Sullivan To: pgsql-performance@postgresql.org Subject: Re: 7.4 Checkpoint Question Message-ID: <20071129160219.GJ6226@crankycanuck.ca> Mail-Followup-To: Andrew Sullivan , pgsql-performance@postgresql.org References: <1196349054.5651.19.camel@bnicholson-desktop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1196349054.5651.19.camel@bnicholson-desktop> User-Agent: Mutt/1.5.13 (2006-08-11) X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200711/374 X-Sequence-Number: 27789 On Thu, Nov 29, 2007 at 10:10:54AM -0500, Brad Nicholson wrote: > This is a _really _low volume system, less than 500 writes/hour. Normal > operation sees checkpoint related spikes of around 200-300 milliseconds. > We always checkpoint at the checkpoint timeout (every 5 minutes). > During this one checkpoint, I'm seeing transactions running 2-3 seconds. > During this time, writes are < 5/minute. > What gives? pg_dump? Remember that it has special locks approximately equivalent (actually eq? I forget) with SERIALIZABLE mode, which makes things rather different. A -- Andrew Sullivan Old sigs will return after re-constitution of blue smoke