Re: Curious about dead rows.

From: Brad Nicholson <bnichols(at)ca(dot)afilias(dot)info>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Russell Smith <mr-russ(at)pws(dot)com(dot)au>, Jean-David Beyer <jeandavid8(at)verizon(dot)net>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Curious about dead rows.
Date: 2007-11-16 15:56:48
Message-ID: 1195228608.8966.364.camel@bnicholson-desktop
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-performance

On Wed, 2007-11-14 at 17:46 -0500, Tom Lane wrote:
> Russell Smith <mr-russ(at)pws(dot)com(dot)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.

In response to

Responses

Browse pgsql-performance by date

  From Date Subject
Next Message Jonah H. Harris 2007-11-16 16:06:11 Re: PostgreSQL vs MySQL, and FreeBSD
Previous Message Dave Dutcher 2007-11-16 15:56:28 Re: PostgreSQL vs MySQL, and FreeBSD