Received: from localhost (maia-4.hub.org [200.46.204.183]) by postgresql.org (Postfix) with ESMTP id 855A49FBE1B; Fri, 30 Mar 2007 07:36:58 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 79638-03; Fri, 30 Mar 2007 07:36:55 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.4 X-Greylist: from auto-whitelisted by SQLgrey-1.7.4 Received: from mail.metronet.co.uk (mail.metronet.co.uk [213.162.97.75]) by postgresql.org (Postfix) with ESMTP id 8E8369FBD9D; Fri, 30 Mar 2007 07:36:55 -0300 (ADT) Received: from server3.office.archonet.com (84-51-143-99.archon037.adsl.metronet.co.uk [84.51.143.99]) by smtp.metronet.co.uk (MetroNet Mail) with ESMTP id 69349747A3; Fri, 30 Mar 2007 11:27:11 +0100 (BST) Received: from [192.168.1.36] (dell36.office.archonet.com [192.168.1.36]) by server3.office.archonet.com (Postfix) with ESMTP id 4118F27408E; Fri, 30 Mar 2007 11:27:11 +0100 (BST) Message-ID: <460CE5FE.5050906@archonet.com> Date: Fri, 30 Mar 2007 11:27:10 +0100 From: Richard Huxton User-Agent: IceDove 1.5.0.9 (X11/20061220) MIME-Version: 1.0 To: Simon Riggs Cc: Zeugswetter Andreas ADI SD , Koichi Suzuki , josh@agliodbs.com, pgsql-hackers@postgresql.org, pgsql-patches@postgresql.org Subject: Re: [PATCHES] Full page writes improvement, code update References: <460886E8.6040907@oss.ntt.co.jp> <4609CAC3.7060008@oss.ntt.co.jp> <1175072848.4386.323.camel@silverbirch.site> <200703291145.28574.josh@agliodbs.com> <1175200117.4386.616.camel@silverbirch.site> <460C611E.6090800@oss.ntt.co.jp> <1175249717.4386.716.camel@silverbirch.site> In-Reply-To: <1175249717.4386.716.camel@silverbirch.site> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200703/1765 X-Sequence-Number: 101249 Simon Riggs wrote: > On Fri, 2007-03-30 at 10:22 +0200, Zeugswetter Andreas ADI SD wrote: >>> Without a switch, because both full page writes and >>> corresponding logical log is included in WAL, this will >>> increase WAL size slightly >>> (maybe about five percent or so). If everybody is happy >>> with this, we >>> don't need a switch. >> Sorry, I still don't understand that. What is the "corresponding logical >> log" ? >> It seems to me, that a full page WAL record has enough info to produce a >> >> dummy LSN WAL entry. So insead of just cutting the full page wal record >> you >> could replace it with a LSN WAL entry when archiving the log. >> >> Then all that is needed is the one flag, no extra space ? > > The full page write is required for crash recovery, but that isn't > required during archive recovery because the base backup provides the > safe base. Is that always true? Could the backup not pick up a partially-written page? Assuming it's being written to as the backup is in progress. (We are talking about when disk blocks are smaller than PG blocks here, so can't guarantee an atomic write for a PG block?) -- Richard Huxton Archonet Ltd