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From: Bill Moran <wmoran@collaborativefusion.com>
To: Laurent Raufaste <analogue@glop.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: PG writes a lot to the disk
Date: Fri, 21 Mar 2008 09:54:37 -0400
Message-ID: <20080321095437.2a4a9ce6.wmoran@collaborativefusion.com> (raw)
In-Reply-To: <669dc9710803210645m530b492cs6de98f215bcecb23@mail.gmail.com>
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	<20080320105833.c539476d.wmoran@collaborativefusion.com>
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	<669dc9710803210645m530b492cs6de98f215bcecb23@mail.gmail.com>

In response to "Laurent Raufaste" <analogue@glop.org>:

> 2008/3/21, Gregory Stark <stark@enterprisedb.com>:
> >
> > Well that's true it does. But only once per row. So analyze would have set the
> >  bit on every row. You could do the same thing with something ligter like
> >  "select count(*) from <table>".
> 
> Well, the table has been analyzed, I did SELECT, PG write on the
> table. That's a fact.
> 
> But it's also true (I juste tested it) that every file of a table is
> modified by a SELECT COUNT.

The real question (to verify Tom's point) is does a _second_ SELECT count()
modify the table again?  If so, then something else is going on than
what Tom suggested.

-- 
Bill Moran
Collaborative Fusion Inc.
http://people.collaborativefusion.com/~wmoran/

wmoran@collaborativefusion.com
Phone: 412-422-3463x4023



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