Received: from localhost (unknown [200.46.204.183]) by developer.postgresql.org (Postfix) with ESMTP id 67B242E0120 for ; Thu, 15 May 2008 05:00:17 -0300 (ADT) Received: from developer.postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 10509-01-4 for ; Thu, 15 May 2008 04:59:47 -0300 (ADT) 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 developer.postgresql.org (Postfix) with ESMTP id 33B2C2E01AA for ; Thu, 15 May 2008 04:07:11 -0300 (ADT) 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 m4F7798H028389; Thu, 15 May 2008 03:07:09 -0400 (EDT) To: Greg Smith cc: Alvaro Herrera , pgsql-performance@postgresql.org Subject: Re: I/O on select count(*) In-reply-to: References: <920841.71690.qm@web44808.mail.sp1.yahoo.com> <482B1D5F.EE98.0025.0@wicourts.gov> <20080515020553.GN9838@alvh.no-ip.org> Comments: In-reply-to Greg Smith message dated "Wed, 14 May 2008 22:21:45 -0400" Date: Thu, 15 May 2008 03:07:09 -0400 Message-ID: <28388.1210835229@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200805/199 X-Sequence-Number: 30167 Greg Smith writes: > ... To put that another way: if I've run a manual vacuum, is it true > that it will have updated all the hint bits to XMIN_COMMITTED for all the > tuples that were all done when the vacuum started? Any examination whatsoever of a tuple --- whether by vacuum or any ordinary DML operation --- will update its hint bits to match the commit/abort status of the inserting/deleting transaction(s) as of the instant of the examination. Your statement above is true but is weaker than reality. regards, tom lane