X-Original-To: pgsql-performance-postgresql.org@postgresql.org Received: from localhost (mx1.hub.org [200.46.208.251]) by postgresql.org (Postfix) with ESMTP id 96F429FA15C for ; Tue, 12 Sep 2006 20:42:53 -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 52965-01-4 for ; Tue, 12 Sep 2006 20:42:47 -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 1A4269FA50F for ; Tue, 12 Sep 2006 20:42:32 -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 k8CNgUSE003216; Tue, 12 Sep 2006 19:42:30 -0400 (EDT) To: mischa@ca.sophos.com cc: pgsql-performance@postgresql.org Subject: Re: Bad plan for join to aggregate of join. In-reply-to: <45071FCC.8090509@ca.sophos.com> References: <821wqiy0oc.fsf@mid.bfk.de> <45071FCC.8090509@ca.sophos.com> Comments: In-reply-to Mischa Sandberg message dated "Tue, 12 Sep 2006 13:59:56 -0700" Date: Tue, 12 Sep 2006 19:42:30 -0400 Message-ID: <3215.1158104550@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0.109 tagged_above=0 required=5 tests=AWL, SPF_HELO_PASS, SPF_PASS X-Spam-Level: X-Archive-Number: 200609/107 X-Sequence-Number: 20793 Mischa Sandberg writes: > can PG see that a join on an grouped-by field > can be pushed down into the query as an indexable filter? No. The GROUP BY serves as a partial optimization fence. If you're concerned about the speed of this query, I recommend making a different view in which 'message' is joined inside the GROUP BY. regards, tom lane