Received: from localhost (maia-2.hub.org [200.46.204.187]) by postgresql.org (Postfix) with ESMTP id D45F39FBA49 for ; Mon, 25 Jun 2007 12:00:53 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.187]) (amavisd-maia, port 10024) with ESMTP id 40526-04-5 for ; Mon, 25 Jun 2007 12:00:49 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.4 Received: from oxford.xeocode.com (unknown [62.232.55.118]) by postgresql.org (Postfix) with ESMTP id 93B369FBAB8 for ; Mon, 25 Jun 2007 12:00:41 -0300 (ADT) Received: from localhost ([127.0.0.1] helo=oxford.xeocode.com) by oxford.xeocode.com with esmtp (Exim 4.67) (envelope-from ) id 1I2q3F-0001NF-Bn; Mon, 25 Jun 2007 16:00:25 +0100 From: Gregory Stark To: "Tom Lane" Cc: "Koichi Suzuki" , "Simon Riggs" , "Toru SHIMOGAKI" , "Dan Gorman" , Subject: Re: PITR Backups In-Reply-To: <28289.1182781909@sss.pgh.pa.us> (Tom Lane's message of "Mon, 25 Jun 2007 10:31:49 -0400") Organization: EnterpriseDB References: <7E0807EE-B970-4869-A248-B838E42AD9EE@hi5.com> <9761.1182472005@sss.pgh.pa.us> <467B3459.9030808@oss.ntt.co.jp> <1182509748.9276.178.camel@silverbirch.site> <467F938F.1030708@oss.ntt.co.jp> <28289.1182781909@sss.pgh.pa.us> X-Draft-From: ("nnimap+mail01.enterprisedb.com:INBOX.performance" 1309) Date: Mon, 25 Jun 2007 16:00:25 +0100 Message-ID: <87fy4guliu.fsf@oxford.xeocode.com> User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200706/571 X-Sequence-Number: 25604 "Tom Lane" writes: > AFAIK, actually workable methods of this type depend on filesystem > cooperation, and are able to produce coherent snapshots of the logical > (not necessarily physical) filesystem content at a specific instant. I think you need filesystem cooperation in order to provide access to the snapshot somewhere. But the actual snapshotting is done at a very low level by intercepting any block writes and stashing away the old version before writing or alternately by noting the new version and redirecting any reads to the new version. I concur that anything that doesn't allow concurrent i/o while the snapshotting is happening is worthless. It sounds like you're just dd'ing from the device which is pretty much guaranteed not to work. Even if Postgres didn't do any i/o there's nothing stopping the OS and filesystem from issuing i/o. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com