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Re: Autovacuum versus rolled-back transactions

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Autovacuum versus rolled-back transactions
Date: 2007-06-01 02:21:08
Message-ID: 20070601022108.GA7994@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-hackers
Tom Lane wrote:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> > If we apply Heikki's idea of advancing OldestXmin, I think what we
> > should do is grab the value from pgstats when vacuum starts, and each
> > time we're going to advance OldestXmin, grab the value from pgstats
> > again; accumulate the differences from the various pgstat grabs.  At the
> > end we send the accumulated differences as the new dead tuple count.
> 
> Considering that each of those values will be up to half a second old,
> I can hardly think that this will accomplish anything except to
> introduce a great deal of noise ...

Normally, yes, but the values can be older if the vacuum_cost_delay is
large.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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