Received: from localhost (maia-5.hub.org [200.46.204.182]) by postgresql.org (Postfix) with ESMTP id 1FD5A9FB82D for ; Wed, 6 Jun 2007 11:40:57 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.182]) (amavisd-maia, port 10024) with ESMTP id 59727-05 for ; Wed, 6 Jun 2007 11:40:46 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.4 Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by postgresql.org (Postfix) with ESMTP id 9B6EA9FB6BA for ; Wed, 6 Jun 2007 11:40:52 -0300 (ADT) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.14.1/8.14.1) with ESMTP id l56Eef3X020760; Wed, 6 Jun 2007 10:40:42 -0400 (EDT) To: weiping cc: pgsql-performance@postgresql.org Subject: Re: weird query plan In-reply-to: <46662DE7.4030602@pgsqldb.com> References: <46662DE7.4030602@pgsqldb.com> Comments: In-reply-to weiping message dated "Wed, 06 Jun 2007 11:45:43 +0800" Date: Wed, 06 Jun 2007 10:40:41 -0400 Message-ID: <20759.1181140841@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200706/93 X-Sequence-Number: 25126 weiping writes: > -> Index Scan using urlusermaps_userid on wd_urlusermaps a > (cost=0.00..6750.55 rows=1094 width=96) (actual time=0.544..5.616 > rows=41 loops=1) > Index Cond: (userid = 219177) > Filter: ("share" = 1) > the userid=219177 got 2000+ record and around 40 shared=1, why above 2 query > shows so much difference? Probably because the rowcount estimate is so far off (1094 vs 41). Possibly boosting the statistics target would help. regards, tom lane