From: Bill Moran <wmoran@collaborativefusion.com>
To: Douglas J Hunley <doug@hunley.homeip.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: questions about CLUSTER
Date: Wed, 27 Feb 2008 14:34:49 -0500
Message-ID: <20080227143449.adaea949.wmoran@collaborativefusion.com> (raw)
In-Reply-To: <200802271345.11897.doug@hunley.homeip.net>
References: <200802271101.57169.doug@hunley.homeip.net>
<20080227124057.9b3937ce.wmoran@collaborativefusion.com>
<200802271335.16397.doug@hunley.homeip.net>
<200802271345.11897.doug@hunley.homeip.net>
In response to Douglas J Hunley <doug@hunley.homeip.net>:
> On Wednesday 27 February 2008 13:35:16 Douglas J Hunley wrote:
> > > > 2) is there any internal data in the db that would allow me to
> > > > programmatically determine which tables would benefit from being
> > > > clustered? 3) for that matter, is there info to allow me to determine
> > > > which index it should be clustered on in cases where the table has more
> > > > than one index?
> > >
> > > The pg_stat_user_indexes table keeps stats on how often the index is
> > > used. Indexes that are used frequently are candidates for clustering.
> >
> > I had just started looking at this actually.
>
> ok, so for a follow-on, should I be more concerned with idx_scan,
> idx_tup_read, or idx_tup_fetch when determining which indexes are 'good'
> candidates?
Again, not an easy question to answer, as it's probably different for
different people.
idx_scan is the count of how many times the index was used.
idx_tup_read and idx_tup_fetch are counts of how much data has been
accessed by using the index.
This part of the docs has more:
http://www.postgresql.org/docs/8.2/static/monitoring-stats.html
So, you'll probably have to watch all of those if you want to determine
when to automate clustering operations.
Personally, if I were you, I'd set up a test box and make sure
clustering makes enough of a difference to be doing all of this work.
> again, tia. i feel like such a noob around here :)
Bah ... we all start out as noobs. Just don't go googling for my posts
from years back, it's embarrassing ...
--
Bill Moran
Collaborative Fusion Inc.
http://people.collaborativefusion.com/~wmoran/
wmoran@collaborativefusion.com
Phone: 412-422-3463x4023
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To: pgsql-performance@postgresql.org
Cc: wmoran@collaborativefusion.com, doug@hunley.homeip.net
Subject: Re: questions about CLUSTER
In-Reply-To: <20080227143449.adaea949.wmoran@collaborativefusion.com>
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