Received: from localhost (unknown [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 91D519F9B82 for ; Mon, 10 Sep 2007 18:59:43 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.184]) (amavisd-maia, port 10024) with ESMTP id 11220-10 for ; Mon, 10 Sep 2007 18:59:35 -0300 (ADT) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.5 Received: from ug-out-1314.google.com (ug-out-1314.google.com [66.249.92.173]) by postgresql.org (Postfix) with ESMTP id 61FFC9F9BD2 for ; Mon, 10 Sep 2007 18:59:40 -0300 (ADT) Received: by ug-out-1314.google.com with SMTP id j3so455777ugf for ; Mon, 10 Sep 2007 14:59:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; 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; bh=NeDm1Waf87AYCTI5p6rNWSs2LrcqJ7GpwmHHaRYB4FI=; b=XaV+1mD/SxEHrDIt8uFCOIdcKx/qsP3x+dzR9XwnrGTHsGrL1IOqNJQQnccAXrPSnvOgSGoEZcdMxqD6+BoSNweX+60bmGftkqkBknKdhqylHxEAT3IHBMU3K5bZcQx0c8Innb/EnuCjZZ22GHtFEOCQ9LPBXwXAR/lxM19pKVI= 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=Q/6XKtQ0Sy5x6YBNQRhNWldo00rlyP3uNmRcad+wPqx53wFl6sPQhRFH1c1ApCkg/Ap5QMyFXeOlb4fsyDeE4S0MCKuLh6g5jVYsJ07zSrhzpT+hqWVHTiTny/5BeTF2xky+n17AjyMDjzT+YENOhsr33AniTNYCR5EJXJCUOGM= Received: by 10.67.16.2 with SMTP id t2mr5127372ugi.1189461578363; Mon, 10 Sep 2007 14:59:38 -0700 (PDT) Received: by 10.66.220.7 with HTTP; Mon, 10 Sep 2007 14:59:38 -0700 (PDT) Message-ID: Date: Mon, 10 Sep 2007 16:59:38 -0500 From: "Scott Marlowe" To: "Gregory Stark" Subject: Re: random_page_costs - are defaults of 4.0 realistic for SCSI RAID 1 Cc: "Luke Lonergan" , "Carlo Stonebanks" , pgsql-performance@postgresql.org In-Reply-To: <87y7fekxga.fsf@oxford.xeocode.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <87y7fekxga.fsf@oxford.xeocode.com> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200709/163 X-Sequence-Number: 26708 On 9/10/07, Gregory Stark wrote: > > "Luke Lonergan" writes: > > > Should be a lot higher, something like 10-15 is approximating accurate. > > Most people's experience is that due to Postgres underestimating the benefits > of caching lowering the random_page_cost is helpful. Quite often the real problem is that they have effective_cache_size too small, and they use random_page_cost to get the planner to switch to index scans on small tables. With a large effective_cache_size and small to moderate table (i.e. it fits in memory pretty handily) the planner seems much better in the last few major releases about picking an index over a sequential scan.