X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (mx1.hub.org [200.46.208.251]) by postgresql.org (Postfix) with ESMTP id 7EC1111F623C for ; Tue, 25 Apr 2006 12:55:56 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.208.251]) (amavisd-new, port 10024) with ESMTP id 40731-05 for ; Tue, 25 Apr 2006 12:55:40 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey- Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by postgresql.org (Postfix) with ESMTP id 123AC11F622B for ; Tue, 25 Apr 2006 12:55:39 -0300 (ADT) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.13.6/8.13.6) with ESMTP id k3PFtaVE019862; Tue, 25 Apr 2006 11:55:36 -0400 (EDT) To: arnaulist@andromeiberica.com cc: pgsql-performance@postgresql.org Subject: Re: Query on postgresql 7.4.2 not using index In-reply-to: <444E44A2.6030703@andromeiberica.com> References: <444E240D.3050000@andromeiberica.com> <3c1395330604250634r6f215ceame157f3dd5f5f4fa3@mail.gmail.com> <444E28ED.3090900@andromeiberica.com> <19483.1145978579@sss.pgh.pa.us> <444E44A2.6030703@andromeiberica.com> Comments: In-reply-to Arnau message dated "Tue, 25 Apr 2006 17:47:46 +0200" Date: Tue, 25 Apr 2006 11:55:36 -0400 Message-ID: <19861.1145980536@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200604/552 X-Sequence-Number: 18636 Arnau writes: > I have done the same tests on 8.1.0. Bitmap scans are a totally different animal that doesn't exist in 7.4. A plain indexscan, such as 7.4 knows about, is generally not effective for fetching more than a percent or two of the table. The crossover point for a bitmap scan is much higher (don't know exactly, but probably something like 30-50%). regards, tom lane