To: "Kevin Grittner" <Kevin.Grittner@wicourts.gov>
cc: pgsql-performance@postgresql.org
Subject: Re: LIKE without wildcard different from = 
In-reply-to: <4C59503402000025000341C0@gw.wicourts.gov> 
References: <4C59503402000025000341C0@gw.wicourts.gov>
Comments: In-reply-to "Kevin Grittner" <Kevin.Grittner@wicourts.gov>
	message dated "Wed, 04 Aug 2010 11:34:12 -0500"
Date: Wed, 04 Aug 2010 12:41:47 -0400
Message-ID: <21079.1280940107@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> We have been using the C locale for everything at our site, but
> there is occasionally talk of supporting characters outside the
> ASCII7 set. In playing around with indexing, to see what the impact
> of that would be, I stumbled across something which was mildly
> surprising.

> In the C locale, if you want to search for an exact value which
> doesn't contain wildcard characters, it doesn't matter whether you
> use the 'LIKE' operator or the '=' operator.  With LATIN1 encoding,
> it made three orders of magnitude difference, both in the estimated
> cost and the actual run time.

What PG version are you testing?  8.4 and up should know that an
exact-match pattern can be optimized regardless of the lc_collate
setting.

			regards, tom lane