pattern-match selectivity code and lower(thing) LIKE

On Tue, 07 Aug 2001, Tom Lane wrote:

I'm on 7.1
(PostgreSQL 7.1.2 on i686-pc-linux-gnu, compiled by GCC 2.95.4)

Okay ... [ looks at code ... ] oh, I see the problem. The pattern-match
selectivity code doesn't try to deal with "lower(foo) LIKE ...":

/*
* If expression is not var op constant for
* a simple var of a real relation (no subqueries, for now),
* then punt and return a default estimate.
*/

This could probably be improved, but I don't have time to think
about it now. In the meantime you could try knocking
DEFAULT_MATCH_SEL down a little bit. (It's already been reduced to
0.005 in current sources, in fact.) See
src/backend/utils/adt/selfuncs.c.

Has this improved any since Aug. ? I tried to look in the current CVS,
but I don't know where this code would be. I did a quick find and
couldn't locate the comment shown above anywhere.

(I've returned to my original project, and tried reducing
DEFAULT_MATCH_SEL in 7.1.3 to 0.005 (it was 0.01 in the current cygwin
source); this didn't help so I'm going to use lowercase only entries
in my tables for now so I don't have to index lower(item)).

Nick

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