X-Original-To: pgsql-hackers-postgresql.org@postgresql.org Received: from localhost (wm.hub.org [200.46.204.128]) by postgresql.org (Postfix) with ESMTP id 744FA9FA508 for ; Sun, 23 Jul 2006 21:25:33 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.128]) (amavisd-new, port 10024) with ESMTP id 18535-02 for ; Mon, 24 Jul 2006 00:25:25 +0000 (UTC) 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 785259FA48B for ; Sun, 23 Jul 2006 21:25:25 -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 k6O0PInA028751; Sun, 23 Jul 2006 20:25:19 -0400 (EDT) To: Gavin Sherry cc: Jie Zhang , pgsql-hackers@postgresql.org, Luke Lonergan Subject: Re: On-disk bitmap index patch In-reply-to: References: <28525.1153698215@sss.pgh.pa.us> Comments: In-reply-to Gavin Sherry message dated "Mon, 24 Jul 2006 10:06:23 +1000" Date: Sun, 23 Jul 2006 20:25:18 -0400 Message-ID: <28750.1153700718@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200607/1001 X-Sequence-Number: 86856 Gavin Sherry writes: > On Sun, 23 Jul 2006, Tom Lane wrote: >> However, the main problem I've got with this is that a new index AM is a >> pretty large burden, and no one's made the slightest effort to sell >> pghackers on taking this on. > For low cardinality sets, bitmaps greatly out perform btree. If the column is sufficiently low cardinality, you might as well just do a seqscan --- you'll be hitting most of the heap's pages anyway. I'm still waiting to be convinced that there's a sweet spot wide enough to justify supporting another index AM. (I'm also wondering whether this doesn't overlap the use-case for GIN.) regards, tom lane