X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by postgresql.org (Postfix) with ESMTP id CC3D59DC9D0 for ; Sat, 11 Mar 2006 07:33:04 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 37541-05 for ; Sat, 11 Mar 2006 07:33:07 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey- Received: from peufeu.com (boutiquenumerique.com [82.67.9.10]) by postgresql.org (Postfix) with ESMTP id 879509DC943 for ; Sat, 11 Mar 2006 07:33:02 -0400 (AST) Received: (qmail 8677 invoked from network); 11 Mar 2006 12:33:51 +0100 Received: from boutiquenumerique.com (HELO apollo13) (82.67.9.10) by boutiquenumerique.com with SMTP; 11 Mar 2006 12:33:51 +0100 Date: Sat, 11 Mar 2006 12:33:50 +0100 To: "Joost Kraaijeveld" , "David Lang" Subject: Re: x206-x225 Cc: "Richard Huxton" , pgsql-performance@postgresql.org References: <441181C6.3040401@archonet.com> <1142063378.6634.13.camel@localhost> <1142065029.6634.23.camel@localhost> From: PFC Content-Type: text/plain; format=flowed; delsp=yes; charset=utf-8 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Message-ID: In-Reply-To: <1142065029.6634.23.camel@localhost> User-Agent: Opera M2/8.51 (Linux, build 1462) X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0.107 required=5 tests=[AWL=0.107] X-Spam-Score: 0.107 X-Spam-Level: X-Archive-Number: 200603/150 X-Sequence-Number: 17587 >> each transaction requires a sync to the disk, a sync requires a real >> write (which you then wait for), so you can only do one transaction per >> rotation. > Not according to a conversation I had with Western Digital about the It depends if you consider that "written to the disk" means "data is somewhere between the OS cache and the platter" or "data is writter on the platter and will survive a power loss". Postgres wants the second option, of course. For that, the data has to be on the disk. Thus, the disk has to seek, wait till the desired sector arrives in front of the head, write, and tell the OS it's done. Your disk just stores data in its embedded RAM buffer and tells the OS it's written, but if you lose power, you lose anything that's in the disk embedded RAM cache... Advanced RAID cards have battery backed up RAM cache precisely for that purpose. Your harddisk doesn't.