Message-ID: <465717A6.4040503@commandprompt.com>
Date: Fri, 25 May 2007 10:06:46 -0700
From: "Joshua D. Drake" <jd@commandprompt.com>
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To: mark@mark.mielke.cc
CC: Richard Huxton <dev@archonet.com>, Mark Lewis <mark.lewis@mir3.com>,
	James Mansion <james@mansionfamily.plus.com>,
	Magnus Hagander <magnus@hagander.net>,
	Alexander Staubo <alex@purefiction.net>, Andy <frum@ar-sd.net>,
	pgsql-performance@postgresql.org
Subject: Re: LIKE search and performance
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	<4655E64B.5050503@hagander.net>
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	<1180040560.31471.262.camel@archimedes>
	<20070524215450.GA3858@mark.mielke.cc>
	<46569AA5.10205@archonet.com>
	<20070525141630.GA12162@mark.mielke.cc>
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mark@mark.mielke.cc wrote:

> I am speaking of contains, as contains is the one that was said to
> require a seqscan. I am questioning why it requires a seqscan. The
> claim was made that with MVCC, the index is insufficient to check
> for visibility and that the table would need to be accessed anyways,
> therefore a seqscan is required. I question whether a like '%bar%'
> should be considered a high selectivity query in the general case.
> I question whether a worst case should be assumed.

If you are doing %bar% you should be using pg_tgrm or tsearch2.

J


> 
> Perhaps I question too much? :-)
> 
> Cheers,
> mark
>