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 DCB689DC850 for ; Mon, 27 Feb 2006 21:06:15 -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 44058-09 for ; Mon, 27 Feb 2006 21:06:18 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey- Received: from candle.pha.pa.us (candle.pha.pa.us [70.90.9.53]) by postgresql.org (Postfix) with ESMTP id 3C0549DC823 for ; Mon, 27 Feb 2006 21:06:13 -0400 (AST) Received: (from pgman@localhost) by candle.pha.pa.us (8.11.6/8.11.6) id k1S16DK16068; Mon, 27 Feb 2006 20:06:13 -0500 (EST) From: Bruce Momjian Message-Id: <200602280106.k1S16DK16068@candle.pha.pa.us> Subject: Re: fsync and battery-backed caches In-Reply-To: <20060228002223.GW82012@pervasive.com> To: "Jim C. Nasby" Date: Mon, 27 Feb 2006 20:06:13 -0500 (EST) CC: Tino Wildenhain , Javier Somoza , pgsql-performance@postgresql.org X-Mailer: ELM [version 2.4ME+ PL121 (25)] MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0.393 required=5 tests=[AWL=-0.107, RAZOR2_CHECK=0.5] X-Spam-Score: 0.393 X-Spam-Level: X-Archive-Number: 200602/424 X-Sequence-Number: 17410 Jim C. Nasby wrote: > On Mon, Feb 27, 2006 at 11:12:57AM +0100, Tino Wildenhain wrote: > > Javier Somoza schrieb: > > > > > > Hi all > > > > > > Is it secure to disable fsync havin battery-backed disk cache? > > > > > > Thx > > > > > No. fsync moves the data from OS memory cache to disk-adaptor > > cache which is required to benefit from battery backup. > > More importantly, in guarantees that data is committed to non-volatile > storage in such a way that PostgreSQL can recover from a crash without > corruption. > > If you have a battery-backed controller and turn on write caching you > shouldn't see much effect from fsync anyway. We do mention battery-backed cache in our docs: http://www.postgresql.org/docs/8.1/static/wal.html If it is unclear, please let us know. -- Bruce Momjian http://candle.pha.pa.us SRA OSS, Inc. http://www.sraoss.com + If your life is a hard drive, Christ can be your backup. +