From: Brad Nicholson <bnichols@ca.afilias.info>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Russell Smith <mr-russ@pws.com.au>
Cc: Jean-David Beyer <jeandavid8@verizon.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: Curious about dead rows.
Date: Fri, 16 Nov 2007 10:56:48 -0500
Message-ID: <1195228608.8966.364.camel@bnicholson-desktop> (raw)
In-Reply-To: <16999.1195080384@sss.pgh.pa.us>
References: <4735DBDB.5050208@verizon.net>
<16627.1194714491@sss.pgh.pa.us>
<4735FA9F.1080805@verizon.net>
<b42b73150711131628q1469df3el6f557e10de07a05@mail.gmail.com>
<473A5CC0.3060003@verizon.net>
<b42b73150711131936l65b97b9ya7953383673b2710@mail.gmail.com>
<473AE63D.7090305@verizon.net>
<20071114152249.GA16041@crankycanuck.ca>
<473B2A1F.30804@verizon.net>
<473B6C9D.1020804@pws.com.au>
<16999.1195080384@sss.pgh.pa.us>
On Wed, 2007-11-14 at 17:46 -0500, Tom Lane wrote:
> Russell Smith <mr-russ@pws.com.au> 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
--
Brad Nicholson 416-673-4106
Database Administrator, Afilias Canada Corp.
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To: pgsql-performance@postgresql.org
Cc: bnichols@ca.afilias.info, tgl@sss.pgh.pa.us, mr-russ@pws.com.au, jeandavid8@verizon.net
Subject: Re: Curious about dead rows.
In-Reply-To: <1195228608.8966.364.camel@bnicholson-desktop>
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