X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by svr1.postgresql.org (Postfix) with ESMTP id 8FC3BDB098 for ; Thu, 27 Oct 2005 18:02:04 -0300 (ADT) Received: from svr1.postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 29036-09 for ; Thu, 27 Oct 2005 21:01:59 +0000 (GMT) Received: from h1.bettercom.de (h1.bettercom.de [213.239.194.41]) by svr1.postgresql.org (Postfix) with ESMTP id 42853DB0E4 for ; Thu, 27 Oct 2005 18:01:59 -0300 (ADT) Received: (qmail 2678 invoked by uid 208); 27 Oct 2005 21:02:00 -0000 Received: from 213.39.214.61 by h1 (envelope-from , uid 0) with qmail-scanner-1.23 (clamdscan: 0.87. spamassassin: 3.04. Clear:RC:1(213.39.214.61):. Processed in 0.96462 secs); 27 Oct 2005 21:02:00 -0000 Received: from unknown (HELO nb-aspire.bettercom.de) ([213.39.214.61]) (envelope-sender ) by h1.bettercom.de (qmail-ldap-1.03) with SMTP for ; 27 Oct 2005 21:01:57 -0000 Received: (nullmailer pid 10410 invoked by uid 1000); Thu, 27 Oct 2005 21:01:55 -0000 Cc: Denis , pgsql-performance@postgresql.org Subject: Re: Reasons and drawbacks for unused item pointers (was: Update using primary key slow) X-PGP-Key: http://bettercom.de/misc/3A547DE6.asc X-Face: "d[&>8')a)wbF:+L#^<_cohnX6#m5RCCeKF/6_gD(iQ9bX?xe2~Aq*!')D(1ks`?YhomOYbL3R:{4e4a]qft_]<.q/Lf4hIr,`G+LX33&TYp}XGfe~^5m$28R"$C(EwnB\n8t In-Reply-To: <23322.1130442063@sss.pgh.pa.us> (Tom Lane's message of "Thu, 27 Oct 2005 15:41:03 -0400") References: <19722.1130429883@sss.pgh.pa.us> <23322.1130442063@sss.pgh.pa.us> To: pgsql-performance@postgresql.org From: Martin Lesser Date: Thu, 27 Oct 2005 23:01:55 +0200 Message-ID: <87y84eznb0.fsf_-_@nb-aspire.bettercom.de> User-Agent: Gnus/5.1007 (Gnus v5.10.7) XEmacs/21.4 (Jumbo Shrimp, linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0.013 required=5 tests=[AWL=0.013] X-Spam-Score: 0.013 X-Spam-Level: X-Archive-Number: 200510/430 X-Sequence-Number: 15198 Tom Lane writes: > Denis writes: >> There were 1905028 unused item pointers. > The "unused item pointers" number seems a bit high, but otherwise that > looks pretty reasonable. > > Is it possible that the particular row you were updating has been > updated quite a lot of times since the last vacuum? Or even quite > a few times within a single transaction? What causes this "unused item pointers" and which impact do they have regarding performance? If I understood your last posting correctly more than one update on a single row between two vacuum's would i.e. result in one ore more "unused item pointer". Does this slow down the vacuum process and/or other processes? Until now I could not find an answer what this number implies. Regards Martin