X-Original-To: pgsql-hackers-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by postgresql.org (Postfix) with ESMTP id 735C49DD54B for ; Mon, 12 Dec 2005 16:40:05 -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 05095-10 for ; Mon, 12 Dec 2005 16:40:05 -0400 (AST) X-Greylist: delayed 00:34:58.847851 by SQLgrey- Received: from flake.decibel.org (flake.decibel.org [67.100.216.10]) by postgresql.org (Postfix) with ESMTP id EA9B59DCABF for ; Mon, 12 Dec 2005 16:40:02 -0400 (AST) Received: by flake.decibel.org (Postfix, from userid 1001) id B7F3315272; Mon, 12 Dec 2005 14:40:03 -0600 (CST) Date: Mon, 12 Dec 2005 14:40:03 -0600 From: "Jim C. Nasby" To: "Anjan Kumar. A." Cc: pgsql-hackers@postgresql.org Subject: Re: Please Help: PostgreSQL Query Optimizer Message-ID: <20051212204003.GY54639@pervasive.com> References: <17378.1134321553@sss.pgh.pa.us> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: FreeBSD 4.11-RELEASE-p10 i386 X-Distributed: Join the Effort! http://www.distributed.net User-Agent: Mutt/1.5.9i X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0 required=5 tests=[none] X-Spam-Score: 0 X-Spam-Level: X-Archive-Number: 200512/631 X-Sequence-Number: 77479 On Mon, Dec 12, 2005 at 06:39:42PM +0530, Anjan Kumar. A. wrote: > Through googling, i found that Normal Disk has external data transfer rate > of around 40MBps, > where as Main Memory has Data transfer rate ranging from 1.6GBps to 2.8GBps. I think 40MB/s is a burst speed. You should do some testing to verify. In any case, PostgreSQL doesn't come close to the theoretical maximum disk bandwidth even on a sequential scan. There's been discussion about this on various lists in the past. For a single drive, expect something more in the range of 4-6MB/s (depending on the drive). More important that throughput though, is latency. Because the latency on memory is much closer to 0 (it's not truely 0 due to L1/L2 caching), you can serve concurrent requests a lot faster. -- Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461