Received: from localhost (unknown [200.46.204.183]) by developer.postgresql.org (Postfix) with ESMTP id 9DD002E00AE for ; Sun, 18 May 2008 02:48:13 -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 21017-09 for ; Sun, 18 May 2008 02:48:03 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from westnet.com (westnet.com [216.187.52.2]) by developer.postgresql.org (Postfix) with ESMTP id 177192E009A for ; Sun, 18 May 2008 02:28:27 -0300 (ADT) Received: from westnet.com (localhost [127.0.0.1]) by westnet.com (8.14.0/8.14.0) with ESMTP id m4I5SQB5014528 for ; Sun, 18 May 2008 01:28:26 -0400 (EDT) Received: from localhost (gsmith@localhost) by westnet.com (8.14.0/8.13.2/Submit) with ESMTP id m4I5SQH8014525 for ; Sun, 18 May 2008 01:28:26 -0400 (EDT) X-Authentication-Warning: westnet.com: gsmith owned process doing -bs Date: Sun, 18 May 2008 01:28:26 -0400 (EDT) From: Greg Smith X-X-Sender: gsmith@westnet.com To: pgsql-performance@postgresql.org Subject: Re: I/O on select count(*) In-Reply-To: <18382.1210992302@sss.pgh.pa.us> Message-ID: References: <920841.71690.qm@web44808.mail.sp1.yahoo.com> <482B1D5F.EE98.0025.0@wicourts.gov> <20080515020553.GN9838@alvh.no-ip.org> <20080515155232.GC8221@alvh.no-ip.org> <20080516201528.GJ13061@alvh.no-ip.org> <18382.1210992302@sss.pgh.pa.us> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200805/263 X-Sequence-Number: 30231 I just collected all the good internals information included in this thread and popped it onto http://wiki.postgresql.org/wiki/Hint_Bits where I'll continue to hack away at the text until it's readable. Thanks to everyone who answered my questions here, that's good progress toward clearing up a very underdocumented area. I note a couple of potential TODO items not on the official list yet that came up during this discussion: -Smooth latency spikes when switching commit log pages by preallocating cleared pages before they are needed -Improve bulk loading by setting "frozen" hint bits for tuple inserts which occur within the same database transaction as the creation of the table into which they're being inserted Did I miss anything? I think everything brought up falls either into one of those two or the existing "Consider having the background writer update the transaction status hint bits..." TODO. -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD