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 5A1A49DC803 for ; Wed, 15 Feb 2006 19:51:29 -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 55613-10 for ; Wed, 15 Feb 2006 19:51:31 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey- Received: from smtp.nildram.co.uk (smtp.nildram.co.uk [195.112.4.54]) by postgresql.org (Postfix) with ESMTP id 494759DC800 for ; Wed, 15 Feb 2006 19:51:27 -0400 (AST) Received: from [192.168.0.5] (unknown [84.12.26.47]) by smtp.nildram.co.uk (Postfix) with ESMTP id 03DD5253B4D; Wed, 15 Feb 2006 23:51:26 +0000 (GMT) Subject: Re: Strange Create Index behaviour From: Simon Riggs To: Tom Lane Cc: Gary Doades , pgsql-performance@postgresql.org In-Reply-To: <20005.1140040283@sss.pgh.pa.us> References: <43F38867.6010701@gpdnet.co.uk> <19510.1140036968@sss.pgh.pa.us> <19779.1140038874@sss.pgh.pa.us> <43F39E53.1020009@gpdnet.co.uk> <20005.1140040283@sss.pgh.pa.us> Content-Type: text/plain Date: Wed, 15 Feb 2006 23:51:21 +0000 Message-Id: <1140047481.12131.205.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Content-Transfer-Encoding: 7bit X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0.086 required=5 tests=[AWL=0.086] X-Spam-Score: 0.086 X-Spam-Level: X-Archive-Number: 200602/227 X-Sequence-Number: 17213 On Wed, 2006-02-15 at 16:51 -0500, Tom Lane wrote: > 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. Agreed. Good analysis... Best Regards, Simon Riggs