Received: from localhost (unknown [200.46.208.211]) by mail.postgresql.org (Postfix) with ESMTP id CDF9C6336EB for ; Thu, 7 Jan 2010 23:43:44 -0400 (AST) Received: from mail.postgresql.org ([200.46.204.86]) by localhost (mx1.hub.org [200.46.208.211]) (amavisd-maia, port 10024) with ESMTP id 08549-04 for ; Fri, 8 Jan 2010 03:43:24 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by mail.postgresql.org (Postfix) with ESMTP id 19EE2632A0A for ; Thu, 7 Jan 2010 23:43:33 -0400 (AST) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.14.2/8.14.2) with ESMTP id o083hLNa025624; Thu, 7 Jan 2010 22:43:21 -0500 (EST) To: Craig Ringer cc: "Gurgel, Flavio" , Lefteris , pgsql-performance@postgresql.org, Ivan Voras Subject: Re: Air-traffic benchmark In-reply-to: <4B46A6FD.5070106@postnewspapers.com.au> References: <32176465.41521262879116337.JavaMail.root@mail.4linux.com.br> <4B46A6FD.5070106@postnewspapers.com.au> Comments: In-reply-to Craig Ringer message dated "Fri, 08 Jan 2010 11:31:09 +0800" Date: Thu, 07 Jan 2010 22:43:21 -0500 Message-ID: <25623.1262922201@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.527 tagged_above=-10 required=5 tests=AWL=-0.787, BAYES_20=-0.74 X-Spam-Level: X-Archive-Number: 201001/134 X-Sequence-Number: 37014 Craig Ringer writes: > Can Pg even read partial records ? I thought it all operated on a page > level, where if an index indicates that a particular value is present on > a page the whole page gets read in and all records on the page are > checked for the value of interest. No? The whole page gets read, but we do know which record on the page the index entry is pointing at. (This statement is an oversimplification, because of lossy indexes and lossy bitmap scans, but most of the time it's not a matter of "checking all records on the page".) regards, tom lane