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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Matteo Beccati <php@beccati.com>
Cc: Andrea Arcangeli <andrea@cpushare.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
Date: Tue, 10 Jan 2006 22:40:30 -0500
Message-ID: <7924.1136950830@sss.pgh.pa.us> (raw)
In-Reply-To: <1136936205.21025.507.camel@localhost.localdomain>
References: <20060110014447.GB18474@opteron.random>
	<24021.1136858688@sss.pgh.pa.us>
	<20060110022303.GA20168@opteron.random>
	<24372.1136861684@sss.pgh.pa.us>
	<43C3799D.5030103@beccati.com>
	<1625.1136915395@sss.pgh.pa.us>
	<1136930796.21025.486.camel@localhost.localdomain>
	<6398.1136931685@sss.pgh.pa.us>
	<1136936205.21025.507.camel@localhost.localdomain>

Simon Riggs <simon@2ndquadrant.com> writes:
> I meant use the same sampling approach as I was proposing for ANALYZE,
> but do this at plan time for the query. That way we can apply the
> function directly to the sampled rows and estimate selectivity. 

I think this is so unlikely to be a win as to not even be worth spending
any time discussing.  The extra planning time across all queries will
vastly outweigh the occasional improvement in plan choice for some
queries.

			regards, tom lane



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