From: Tom Lane <tgl@sss.pgh.pa.us>
To: Guillaume Smet <guillaume.smet@gmail.com>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: Estimation problem with a LIKE clause containing a /
Date: Wed, 07 Nov 2007 11:34:52 -0500
Message-ID: <17767.1194453292@sss.pgh.pa.us> (raw)
In-Reply-To: <1d4e0c10711070453q214f089cpd144cbb5193d3c4f@mail.gmail.com>
References: <1d4e0c10711070453q214f089cpd144cbb5193d3c4f@mail.gmail.com>
"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
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Subject: Re: Estimation problem with a LIKE clause containing a /
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