From: Merlin Moncure <mmoncure@gmail.com>
To: Brad Nicholson <bnichols@ca.afilias.info>
Cc: 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 17:01:19 -0500
Message-ID: <b42b73150711161401p13e93e4dn19bc8388a2da9208@mail.gmail.com> (raw)
In-Reply-To: <1195228608.8966.364.camel@bnicholson-desktop>
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<473A5CC0.3060003@verizon.net>
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<473AE63D.7090305@verizon.net>
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<473B6C9D.1020804@pws.com.au>
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<1195228608.8966.364.camel@bnicholson-desktop>
On Nov 16, 2007 10:56 AM, Brad Nicholson <bnichols@ca.afilias.info> wrote:
> 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
I am almost 100% I've seen this behavior in the field...
merlin
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To: pgsql-performance@postgresql.org
Cc: mmoncure@gmail.com, 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: <b42b73150711161401p13e93e4dn19bc8388a2da9208@mail.gmail.com>
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