Received: from localhost (unknown [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 154519F9F1A for ; Mon, 24 Sep 2007 17:18:34 -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 92920-01 for ; Mon, 24 Sep 2007 17:18:15 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.5 Received: from oxford.xeocode.com (unknown [87.127.95.196]) by postgresql.org (Postfix) with ESMTP id 019279F9CE9 for ; Mon, 24 Sep 2007 17:18:27 -0300 (ADT) Received: from localhost.enta.net ([127.0.0.1] helo=oxford.xeocode.com) by oxford.xeocode.com with esmtp (Exim 4.67) (envelope-from ) id 1IZuNt-0001Dz-Nz; Mon, 24 Sep 2007 21:18:25 +0100 To: "Carlo Stonebanks" Cc: Subject: Re: Acceptable level of over-estimation? In-Reply-To: (Carlo Stonebanks's message of "Mon\, 24 Sep 2007 15\:37\:41 -0400") User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.1 (gnu/linux) X-Draft-From: ("nnimap+mail01.enterprisedb.com:INBOX.performance" 2626) References: From: Gregory Stark Organization: EnterpriseDB Date: Mon, 24 Sep 2007 21:18:25 +0100 Message-ID: <87k5qfom0e.fsf@oxford.xeocode.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200709/432 X-Sequence-Number: 26977 "Carlo Stonebanks" writes: > Is there a rule of thumb about when the planner's row estimates are too high? > In particular, when should I be concerned that planner's estimated number of > rows estimated for a nested loop is off? By a factor of 10? 100? 1000? Not really. It's a big enough difference for the planner to make a bad decision or it isn't. But if you pressed me I would say a factor of 10 is bad. A factor of 2 is inevitable in some cases. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com