From: Bill Moran <wmoran@collaborativefusion.com>
To: Ben <bench@silentmedia.com>
Cc: pgsql-general@postgresql.org
Subject: Re: Index bloat of 4x
Date: Wed, 17 Jan 2007 13:01:43 -0500
Message-ID: <20070117130143.9171d2df.wmoran@collaborativefusion.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0701170953150.8626@localhost.localdomain>
References: <20070117093223.bcdb302e.wmoran@collaborativefusion.com>
<Pine.LNX.4.64.0701170953150.8626@localhost.localdomain>
In response to Ben <bench@silentmedia.com>:
> Hey Bill. How do you monitor your shared buffer usage? My understanding
> was that there wasn't a good way to see what was used vs. allocated.
echo "select count(*) from pg_buffercache where reldatabase is not null;" | $PSQL_BIN -P tuples_only -U pgsql postgres | head -1
Of course, you have to install the pg_buffercache contrib module first.
> On Wed, 17 Jan 2007, Bill Moran wrote:
>
> >
> > We just did a bunch of maintenance on one of our production databases that
> > involved a lot of alter tables and moving records about and the like.
> >
> > Afterwards, I did a vacuum full and analyze to get the database back on
> > track -- autovac maintains it under normal operations.
> >
> > Today I decided to run reindex during a slow period, and was shocked to
> > find the database size drop from 165M to 30M. Keep in mind that the
> > 165M is after vacuum full. So, apparently, there was 135M of index bloat?
> > That seems a little excessive to me, especially when the docs claim that
> > reindexing is usually not necessary.
> >
> > This is PostgreSQL 8.1.4. We've got upgrades to 8.2 planned, but it's
> > going to be a few months before we can squeak that into a maintenance
> > window. Additionally, I thought all the big index improvements were
> > added in 7.4.
> >
> > I guess my question is whether or not this is expected. It's obviously
> > not a good thing -- I've noticed that shared buffer usage has dropped
> > dramatically as well (from 28,000 to 7000). I hadn't expected index
> > bloat of this magnitude, and I'm concerned about when the database hits
> > 2 or 3 G in size and has 12G just in indexes that take hours to rebuild.
> >
> > --
> > Bill Moran
> > Collaborative Fusion Inc.
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 6: explain analyze is your friend
> >
>
>
>
>
>
>
--
Bill Moran
Collaborative Fusion Inc.
wmoran@collaborativefusion.com
Phone: 412-422-3463x4023
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To: pgsql-general@postgresql.org
Cc: wmoran@collaborativefusion.com, bench@silentmedia.com
Subject: Re: Index bloat of 4x
In-Reply-To: <20070117130143.9171d2df.wmoran@collaborativefusion.com>
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