X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (unknown [200.46.204.2]) by svr1.postgresql.org (Postfix) with ESMTP id EE9B7D1B4D7 for ; Wed, 28 Apr 2004 13:42:06 -0300 (ADT) Received: from svr1.postgresql.org ([200.46.204.71]) by localhost (neptune.hub.org [200.46.204.2]) (amavisd-new, port 10024) with ESMTP id 25269-10 for ; Wed, 28 Apr 2004 13:42:05 -0300 (ADT) Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by svr1.postgresql.org (Postfix) with ESMTP id AE70CD1B4A3 for ; Wed, 28 Apr 2004 13:42:04 -0300 (ADT) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.12.11/8.12.11) with ESMTP id i3SGfeNQ000425; Wed, 28 Apr 2004 12:41:41 -0400 (EDT) To: "scott.marlowe" Cc: Stephan Szabo , brad-pgperf@duttonbros.com, pgsql-performance@postgresql.org Subject: Re: index usage In-reply-to: References: Comments: In-reply-to "scott.marlowe" message dated "Wed, 28 Apr 2004 09:40:08 -0600" Date: Wed, 28 Apr 2004 12:41:40 -0400 Message-ID: <424.1083170500@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: by amavisd-new at postgresql.org X-Spam-Status: No, hits=0.0 tagged_above=0.0 required=5.0 tests= X-Spam-Level: X-Archive-Number: 200404/487 X-Sequence-Number: 6787 "scott.marlowe" writes: > There are tons of hints that it works this way in how they're written, but > nothing that just comes out and says that with pgsql's mvcc > implementation, an index scan still has to hit the pages that contain the > tuples, so often in pgsql a seq scan is a win where in other databases and > index scan would have been a win? > If not, where would I add it if I were going to write something up for the > docs? Just wondering... AFAIR the only place in the docs that mentions seqscan or indexscan at all is the discussion of EXPLAIN in "Performance Tips". Perhaps a suitably-enlarged version of that section could cover this. regards, tom lane