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From: Joshua D. Drake <jd@commandprompt.com>
To: mark@mark.mielke.cc
Cc: Richard Huxton <dev@archonet.com>
Cc: Mark Lewis <mark.lewis@mir3.com>
Cc: James Mansion <james@mansionfamily.plus.com>
Cc: Magnus Hagander <magnus@hagander.net>
Cc: Alexander Staubo <alex@purefiction.net>
Cc: Andy <frum@ar-sd.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: LIKE search and performance
Date: Fri, 25 May 2007 10:06:46 -0700
Message-ID: <465717A6.4040503@commandprompt.com> (raw)
In-Reply-To: <20070525165633.GA13579@mark.mielke.cc>
References: <009501c79d4c$445428f0$0b00a8c0@mpsro.dom>
	<88daf38c0705230905u1a981102k691b47bd36011a80@mail.gmail.com>
	<4655DE75.4080506@mansionfamily.plus.com>
	<4655E64B.5050503@hagander.net>
	<4655FB8A.1040707@mansionfamily.plus.com>
	<1180040560.31471.262.camel@archimedes>
	<20070524215450.GA3858@mark.mielke.cc>
	<46569AA5.10205@archonet.com>
	<20070525141630.GA12162@mark.mielke.cc>
	<4657023A.20209@archonet.com>
	<20070525165633.GA13579@mark.mielke.cc>

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
> 

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