X-Original-To: pgsql-performance-postgresql.org@postgresql.org Received: from localhost (mx1.hub.org [200.46.208.251]) by postgresql.org (Postfix) with ESMTP id 6DAFA9FA5E6 for ; Sun, 11 Jun 2006 23:50:51 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.208.251]) (amavisd-new, port 10024) with ESMTP id 87932-06 for ; Sun, 11 Jun 2006 23:50:48 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey- Received: from floppy.pyrenet.fr (news.pyrenet.fr [194.116.145.2]) by postgresql.org (Postfix) with ESMTP id 6AD269F9CAA for ; Sun, 11 Jun 2006 23:50:48 -0300 (ADT) Received: by floppy.pyrenet.fr (Postfix, from userid 106) id E59EE3093C; Mon, 12 Jun 2006 04:50:46 +0200 (MET DST) From: "Qingqing Zhou" X-Newsgroups: pgsql.performance Subject: Re: Variation between query runtimes Date: Mon, 12 Jun 2006 10:50:28 +0800 Organization: Hub.Org Networking Services Lines: 20 Message-ID: References: <5809b390606102335j41f734d8j@mail.gmail.com> X-Complaints-To: usenet@news.hub.org X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2800.1807 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1807 To: pgsql-performance@postgresql.org X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200606/125 X-Sequence-Number: 19482 ""John Top-k apad"" wrote > > from pg_stast_get_blocks_fetched i can see that both queries need almost the > same number of disk fetches which is quite reasonable ( the index is > unclustered). > > But as you can see there is a great variation between query > runtimes.Cansomeone explain this differnce? > Can you give a self-contained example (including what you did to clear the file system cache (maybe unmount?) to *not* let the 2nd query to use the file content from the 1st query)? Regards, Qingqing