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Date: Wed, 16 May 2007 12:09:26 -0400
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Guillaume Cottenceau <gc@mnc.ch>
Cc: "Jim C. Nasby" <decibel@decibel.org>,
	Michael Stone <mstone+postgres@mathom.us>, pgsql-performance@postgresql.org
Subject: Re: [doc patch] a slight VACUUM / VACUUM FULL doc improvement
 proposal
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Guillaume Cottenceau wrote:
> "Jim C. Nasby" <decibel 'at' decibel.org> writes:
> 
> > On Wed, May 16, 2007 at 09:41:46AM +0200, Guillaume Cottenceau wrote:
> 
> [...]
> 
> > > Come on, I don't suggest to remove several bold warnings about
> > > it, the best one being "Therefore, frequently using VACUUM FULL
> > > can have an extremely negative effect on the performance of
> > > concurrent database queries." My point is to add the few
> > > additional mentions; I don't think the claims that VACUUM FULL
> > > physically compacts the data, and might be useful in case of too
> > > long time with infrequent VACUUM are incorrect, are they?
> > 
> > Unfortunately they are, to a degree. VACUUM FULL can create a
> > substantial amount of churn in the indexes, resulting in bloated
> > indexes. So often you have to REINDEX after you VACUUM FULL.
> 
> Ok, VACUUM FULL does his job (it physically compacts the data and
> might be useful in case of too long time with infrequent VACUUM),
> but we are going to not talk about it because we often needs a
> REINDEX after it? The natural conclusion would rather be to
> document the fact than REINDEX is needed after VACUUM FULL, isn't
> it?

Maybe, but we should also mention that CLUSTER is a likely faster
workaround.

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