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Re: Estimation problem with a LIKE clause containing a / - Mailing list pgsql-performance

From Tom Lane
Subject Re: Estimation problem with a LIKE clause containing a /
Date
Msg-id 17767.1194453292@sss.pgh.pa.us
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In response to Estimation problem with a LIKE clause containing a /  ("Guillaume Smet" <guillaume.smet@gmail.com>)
Responses Re: Estimation problem with a LIKE clause containing a /  ("Guillaume Smet" <guillaume.smet@gmail.com>)
Re: Estimation problem with a LIKE clause containing a /  (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

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