Received: from localhost (maia-5.hub.org [200.46.204.182]) by postgresql.org (Postfix) with ESMTP id 932AE9FBB09 for ; Tue, 3 Jul 2007 12:27:00 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.182]) (amavisd-maia, port 10024) with ESMTP id 18923-05 for ; Tue, 3 Jul 2007 12:26:56 -0300 (ADT) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.4 Received: from wx-out-0506.google.com (wx-out-0506.google.com [66.249.82.235]) by postgresql.org (Postfix) with ESMTP id 080759FB9C1 for ; Tue, 3 Jul 2007 12:26:55 -0300 (ADT) Received: by wx-out-0506.google.com with SMTP id h29so1386008wxd for ; Tue, 03 Jul 2007 08:26:55 -0700 (PDT) DKIM-Signature: a=rsa-sha1; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=AgXd34+rd8A/ECBietp5wFA7p0gvhBxv/Ghvx5gFX1iVNMmgc5MNDCJhheESrnOsY4ZhKCtFHdmCjSRuB5OB7r77oWgCb8kJL5cA1o7wfTIVGhyXo5STK/yFch0oxA/FAtQkPlnrzPHiy5vah8lcITR9LG5c4boJv4Qc81/YPUI= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=S17Nr81B7B5YQcq8fQKn+t60gnXLXTs3vL0RLjmrG2m+PPEb7svcCkXrREVIj/hW9fcE48IFxbrM6+fy4PtbL3bEebL3xfF9PxazqtCwcnW2g+WBvtKFmxIGsPWeS9joIixcNabUeANAhm+xIvySquZdMQ7265VeoCXlncorIRY= Received: by 10.70.66.18 with SMTP id o18mr6027975wxa.1183476415286; Tue, 03 Jul 2007 08:26:55 -0700 (PDT) Received: by 10.70.90.7 with HTTP; Tue, 3 Jul 2007 08:26:55 -0700 (PDT) Message-ID: <5482c80a0707030826v38c59870ib90599ba43337e72@mail.gmail.com> Date: Tue, 3 Jul 2007 17:26:55 +0200 From: Dimitri To: "Heikki Linnakangas" Subject: Re: Filesystem Direct I/O and WAL sync option Cc: "PostgreSQL Performance" In-Reply-To: <468A65F5.8020800@enterprisedb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <5482c80a0707030754o740c82b6s4598dc668720d014@mail.gmail.com> <468A65F5.8020800@enterprisedb.com> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200707/11 X-Sequence-Number: 25695 Yes, disk drives are also having cache disabled or having cache on controllers and battery protected (in case of more high-level storage) - but is it enough to expect data consistency?... (I was surprised about checkpoint sync, but does it always calls write() anyway? because in this way it should work without fsync)... On 7/3/07, Heikki Linnakangas wrote: > Dimitri wrote: > > I'm very curious to know if we may expect or guarantee any data > > consistency with WAL sync=OFF but using file system mounted in Direct > > I/O mode (means every write() system call called by PG really writes > > to disk before return)... > > You'd have to turn that mode on on the data drives as well to get > consistency, because fsync=off disables checkpoint fsyncs of the data > files as well. > > -- > Heikki Linnakangas > EnterpriseDB http://www.enterprisedb.com >