X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by postgresql.org (Postfix) with ESMTP id DFB189DC803 for ; Wed, 15 Feb 2006 17:51:44 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 25310-10 for ; Wed, 15 Feb 2006 17:51:46 -0400 (AST) 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 5A6599DCB98 for ; Wed, 15 Feb 2006 17:51:42 -0400 (AST) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.13.1/8.13.1) with ESMTP id k1FLpNXS020006; Wed, 15 Feb 2006 16:51:23 -0500 (EST) To: Gary Doades cc: pgsql-performance@postgresql.org Subject: Re: Strange Create Index behaviour In-reply-to: <43F39E53.1020009@gpdnet.co.uk> References: <43F38867.6010701@gpdnet.co.uk> <19510.1140036968@sss.pgh.pa.us> <19779.1140038874@sss.pgh.pa.us> <43F39E53.1020009@gpdnet.co.uk> Comments: In-reply-to Gary Doades message dated "Wed, 15 Feb 2006 21:34:11 +0000" Date: Wed, 15 Feb 2006 16:51:23 -0500 Message-ID: <20005.1140040283@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0.11 required=5 tests=[AWL=0.110] X-Spam-Score: 0.11 X-Spam-Level: X-Archive-Number: 200602/224 X-Sequence-Number: 17210 Gary Doades writes: > Interestingly, if I don't delete the table after a run, but just drop > and re-create the index repeatedly it stays a pretty consistent time, > either repeatedly good or repeatedly bad! This is consistent with the theory of a data-dependent performance problem in qsort. If you don't generate a fresh set of random test data, then you get repeatable runtimes. With a new set of test data, you might or might not hit the not-so-sweet-spot that we seem to have detected. regards, tom lane