Received: from localhost (unknown [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 357902E32A1 for ; Thu, 29 Nov 2007 11:10:42 -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 59486-07 for ; Thu, 29 Nov 2007 11:10:28 -0400 (AST) Received: from mail.libertyrms.com (vgateway.libertyrms.info [207.219.45.62]) by postgresql.org (Postfix) with ESMTP id 036B32E329F for ; Thu, 29 Nov 2007 11:10:36 -0400 (AST) Received: from dba5.int.libertyrms.com ([10.1.3.44]) by mail.libertyrms.com with esmtp (Exim 4.22) id 1Ixl2B-0002ZT-HI for pgsql-performance@postgresql.org; Thu, 29 Nov 2007 10:10:35 -0500 Subject: 7.4 Checkpoint Question From: Brad Nicholson To: pgsql-performance@postgresql.org Content-Type: text/plain Date: Thu, 29 Nov 2007 10:10:54 -0500 Message-Id: <1196349054.5651.19.camel@bnicholson-desktop> Mime-Version: 1.0 X-Mailer: Evolution 2.12.1 Content-Transfer-Encoding: 7bit X-SA-Exim-Mail-From: bnichols@ca.afilias.info X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200711/371 X-Sequence-Number: 27786 I have a legacy system still on 7.4 (I know, I know...the upgrade is coming soon). I have a fairly big spike happening once a day, every day, at the same time. It happens during a checkpoint, no surprise there. I know the solution to the problem (upgrade to a modern version), but what I'm looking for as an explanation as to why one particular checkpoint would be so bad on a low volume system, so I can appease certain management concerns. 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. Relevant settings: shared_buffers = 10000 checkpoint_segments = 30 checkpoint_timeout = 300 What gives? -- Brad Nicholson 416-673-4106 Database Administrator, Afilias Canada Corp.