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Re: First steps with 8.3 and autovacuum launcher

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: "Matthew T(dot) O'Connor" <matthew(at)zeut(dot)net>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, Gregory Stark <stark(at)enterprisedb(dot)com>, Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>, Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: First steps with 8.3 and autovacuum launcher
Date: 2007-10-01 20:50:07
Message-ID: 20071001205007.GI20792@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-hackers
Matthew T. O'Connor escribió:
> Tom Lane wrote:
>> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
>>   
>>> This is an interesting idea, but I think it's attacking the wrong
>>> problem.  To me, the problem here is that an ANALYZE should not block
>>> CREATE INDEX or certain forms of ALTER TABLE.
>>
>> I doubt that that will work; in particular I'm pretty dubious that you
>> can safely make CREATE INDEX and VACUUM run together.  Since they'd be
>> unlikely to be using the identical OldestXmin horizon, you'd likely end
>> up with dangling index entries (ie, CREATE INDEX indexes a tuple that
>> the VACUUM removes shortly afterward).
>
> I think the main issue is ANALYZE not VACUUM (at least in this thread) 
> since it's DB load times that are in question.

Right.  Autovac will not issue VACUUM against the freshly restored
tables anyway, since there are no deleted tuples.

> Can CREATE INDEX and ANALYZE be made to run concurrently?

I don't see why not (except for the fact that both try to update
reltuples and relpages AFAIR, so we would need to be careful about
that).

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

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