To: Bill Moran <wmoran@collaborativefusion.com>
cc: Alvaro Herrera <alvherre@commandprompt.com>, pgsql-general@postgresql.org
Subject: Re: Index bloat of 4x 
In-reply-to: <20070117113216.a6d72185.wmoran@collaborativefusion.com> 
References: <20070117093223.bcdb302e.wmoran@collaborativefusion.com>
	<20070117154251.GG26080@alvh.no-ip.org>
	<20070117113216.a6d72185.wmoran@collaborativefusion.com>
Comments: In-reply-to Bill Moran <wmoran@collaborativefusion.com>
	message dated "Wed, 17 Jan 2007 11:32:16 -0500"
Date: Wed, 17 Jan 2007 11:56:14 -0500
Message-ID: <24871.1169052974@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Bill Moran <wmoran@collaborativefusion.com> writes:
> The entire database was around 28M prior to the upgrades, etc.  Immediately
> after the upgrades, it was ~270M.  Following a vacuum full, it dropped to
> 165M.  Following a database-wide reindex, it dropped to 30M.

As Alvaro said, vacuum full doesn't shrink indexes but in fact bloats them.
(Worst case, they could double in size, if the vacuum moves every row;
there's an intermediate state where there have to be index entries for
both old and new copies of each moved row, to ensure things are
consistent if the vacuum crashes right there.)

So the above doesn't sound too unlikely.  Perhaps we should recommend
vac full + reindex as standard cleanup procedure.  Longer term, maybe
teach vac full to do an automatic reindex if it's moved more than X% of
the rows.  Or forget the current vac full implementation entirely, and
go over to something acting more like CLUSTER ...

			regards, tom lane