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 1787C9FB40D for ; Fri, 22 Sep 2006 13:31:29 -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 91539-02 for ; Fri, 22 Sep 2006 13:31:19 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey- Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by postgresql.org (Postfix) with ESMTP id 7DFD59FA372 for ; Fri, 22 Sep 2006 13:24:37 -0300 (ADT) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.13.6/8.13.6) with ESMTP id k8MGOZLY000781; Fri, 22 Sep 2006 12:24:36 -0400 (EDT) To: "Alex Turner" cc: "Pgsql-Performance ((E-mail))" Subject: Re: Confusion and Questions about blocks read In-reply-to: <33c6269f0609220834x6c10db9xa40d6121825dfd14@mail.gmail.com> References: <33c6269f0609220834x6c10db9xa40d6121825dfd14@mail.gmail.com> Comments: In-reply-to "Alex Turner" message dated "Fri, 22 Sep 2006 11:34:58 -0400" Date: Fri, 22 Sep 2006 12:24:35 -0400 Message-ID: <780.1158942275@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0.099 tagged_above=0 required=5 tests=AWL, SPF_HELO_PASS, SPF_PASS X-Spam-Level: X-Archive-Number: 200609/303 X-Sequence-Number: 20989 "Alex Turner" writes: > Home come the query statistics showed that 229066 blocks where read given > that all the blocks in all the tables put together only total 122968? You forgot to count the indexes. Also, the use of indexscans in the mergejoins probably causes multiple re-reads of some table blocks, depending on just what the physical ordering of the rows is. regards, tom lane