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To: "Guillaume Smet" <guillaume.smet@gmail.com>
cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: Estimation problem with a LIKE clause containing a / 
In-reply-to: <1d4e0c10711070453q214f089cpd144cbb5193d3c4f@mail.gmail.com> 
References: <1d4e0c10711070453q214f089cpd144cbb5193d3c4f@mail.gmail.com>
Comments: In-reply-to "Guillaume Smet" <guillaume.smet@gmail.com>
	message dated "Wed, 07 Nov 2007 13:53:16 +0100"
Date: Wed, 07 Nov 2007 11:34:52 -0500
Message-ID: <17767.1194453292@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Guillaume Smet" <guillaume.smet@gmail.com> writes:
> [ bad estimate for LIKE ]

Hmmm ... what locale are you working in?  I notice that the range
estimator for this pattern would be "ancestors >= '1062/' AND
ancestors < '10620'", which will do the right thing in C locale
but maybe not so much elsewhere.

> Version is PostgreSQL 8.1.8 on i686-redhat-linux-gnu,

You'd probably get better results with 8.2, which has a noticeably
smarter LIKE-estimator, at least for histogram sizes of 100 or more.

			regards, tom lane