Received: from localhost (unknown [200.46.204.183]) by postgresql.org (Postfix) with ESMTP id 6A6BD2E2E02 for ; Fri, 16 Nov 2007 18:01:27 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 84869-06-3 for ; Fri, 16 Nov 2007 18:01:22 -0400 (AST) Received: from nf-out-0910.google.com (nf-out-0910.google.com [64.233.182.184]) by postgresql.org (Postfix) with ESMTP id CDB4A2E2EA0 for ; Fri, 16 Nov 2007 18:01:20 -0400 (AST) Received: by nf-out-0910.google.com with SMTP id f5so829979nfh for ; Fri, 16 Nov 2007 14:01:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; bh=9FFMj/RFtT+v6jrEtZcWJYG9RB2rbXwHlu95kdsvyss=; b=uo8nTZB2yg8/Eys4IIM9aA01eta+d3Y7Wb79qh3bP2HGnShNSkY/t1jDiaetnxo6CDy3GN3ehSbUFwYGknJcchBylBIX0Y0bZhx2y5bdm1oalAQnR3PaWEXUk/wd/KuF+h+q1gb64eWC+zjs9a6DPMna9A+994mv5//vhIXZofc= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=KXkHhA8gKOQy/p9enrUuQfRlvbbijACP5+WFamTDBaCL95dvY7jz03BIYFZSyyJwleglZERQMD1DawQU0IoiIN1Rr9E6N8dEvHGzDQ/6hbW4AwwkK4Zz7wsaFX4r6FiJpDmKusm+673GTcGzV+PrK1amKKJtSFsPlsy2AeVUogA= Received: by 10.78.193.5 with SMTP id q5mr2691063huf.1195250479136; Fri, 16 Nov 2007 14:01:19 -0800 (PST) Received: by 10.78.18.2 with HTTP; Fri, 16 Nov 2007 14:01:19 -0800 (PST) Message-ID: Date: Fri, 16 Nov 2007 17:01:19 -0500 From: "Merlin Moncure" To: "Brad Nicholson" Subject: Re: Curious about dead rows. Cc: "Tom Lane" , "Russell Smith" , "Jean-David Beyer" , pgsql-performance@postgresql.org In-Reply-To: <1195228608.8966.364.camel@bnicholson-desktop> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <4735DBDB.5050208@verizon.net> <473A5CC0.3060003@verizon.net> <473AE63D.7090305@verizon.net> <20071114152249.GA16041@crankycanuck.ca> <473B2A1F.30804@verizon.net> <473B6C9D.1020804@pws.com.au> <16999.1195080384@sss.pgh.pa.us> <1195228608.8966.364.camel@bnicholson-desktop> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200711/252 X-Sequence-Number: 27667 On Nov 16, 2007 10:56 AM, Brad Nicholson wrote: > On Wed, 2007-11-14 at 17:46 -0500, Tom Lane wrote: > > Russell Smith writes: > > > It is possible that analyze is not getting the number of dead rows right? > > > > Hah, I think you are on to something. ANALYZE is telling the truth > > about how many "dead" rows it saw, but its notion of "dead" is "not good > > according to SnapshotNow". Thus, rows inserted by a not-yet-committed > > transaction would be counted as dead. So if these are background > > auto-analyzes being done in parallel with inserting transactions that > > run for awhile, seeing a few not-yet-committed rows would be > > unsurprising. > > > > I wonder if that is worth fixing? I'm not especially concerned about > > the cosmetic aspect of it, but if we mistakenly launch an autovacuum > > on the strength of an inflated estimate of dead rows, that could be > > costly. > > Sounds to me like that could result in autovacuum kicking off while > doing large data loads. This sounds suspiciously like problem someone > on -novice was having - tripping over a windows autovac bug while doing > a data load > > http://archives.postgresql.org/pgsql-novice/2007-11/msg00025.php I am almost 100% I've seen this behavior in the field... merlin