X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by svr1.postgresql.org (Postfix) with ESMTP id B0E13DB1D4 for ; Thu, 10 Nov 2005 12:03:59 -0400 (AST) Received: from svr1.postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 59891-07 for ; Thu, 10 Nov 2005 16:03:55 +0000 (GMT) X-Greylist: from auto-whitelisted by SQLgrey- Received: from vms048pub.verizon.net (vms048pub.verizon.net [206.46.252.48]) by svr1.postgresql.org (Postfix) with ESMTP id 90A7ADB178 for ; Thu, 10 Nov 2005 12:03:55 -0400 (AST) Received: from osgiliath.mathom.us ([70.108.64.202]) by vms048.mailsrvcs.net (Sun Java System Messaging Server 6.2-4.02 (built Sep 9 2005)) with ESMTPA id <0IPQ0055QXTJJOB1@vms048.mailsrvcs.net> for pgsql-performance@postgresql.org; Thu, 10 Nov 2005 10:00:56 -0600 (CST) Received: from localhost (localhost [127.0.0.1]) by osgiliath.mathom.us (Postfix) with ESMTP id 33BDB6001EE; Thu, 10 Nov 2005 11:00:55 -0500 (EST) Received: from osgiliath.mathom.us ([127.0.0.1]) by localhost (osgiliath [127.0.0.1]) (amavisd-new, port 10024) with LMTP id 30964-05-4; Thu, 10 Nov 2005 11:00:55 -0500 (EST) Received: by osgiliath.mathom.us (Postfix, from userid 1000) id 15B296001D7; Thu, 10 Nov 2005 11:00:55 -0500 (EST) Date: Thu, 10 Nov 2005 11:00:55 -0500 From: Michael Stone Subject: Re: WAL sync behaviour In-reply-to: <1131637958.3554.75.camel@state.g2switchworks.com> To: Scott Marlowe Cc: pgsql-performance@postgresql.org Mail-Followup-To: Scott Marlowe , pgsql-performance@postgresql.org Message-id: <20051110160054.GP9905@mathom.us> MIME-version: 1.0 Content-type: text/plain; charset=us-ascii; format=flowed Content-disposition: inline X-Pgp-Fingerprint: 53 FF 38 00 E7 DD 0A 9C 84 52 84 C5 EE DF 7C 88 X-Virus-Scanned: by amavisd-new-20030616-p10 (Debian) at mathom.us References: <20051110133241.GA4031@uio.no> <437355C6.4030604@archonet.com> <20051110142535.GA4530@uio.no> <20051110144309.GO9905@mathom.us> <1131637958.3554.75.camel@state.g2switchworks.com> User-Agent: Mutt/1.5.11 X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0.003 required=5 tests=[AWL=0.003] X-Spam-Score: 0.003 X-Spam-Level: X-Archive-Number: 200511/182 X-Sequence-Number: 15439 On Thu, Nov 10, 2005 at 09:52:38AM -0600, Scott Marlowe wrote: >Not from what I understood. Ext2 can't guarantee that your data will >even be there in any form after a crash. It can if you sync the data. (Which is the whole point of the WAL.) >I believe only metadata journaling is needed though. If you don't sync, metadata journaling doesn't do anything to guarantee that your data will be there, so you're adding no data security in the non-synchronous-write case. (Which is irrelevant for the WAL.) What metadata journalling gets you is fast recovery from crashes by avoiding a fsck. The fsck time is related to the number of files on a filesystem--so it's generally pretty quick on a WAL partition anyway. Mike Stone