Re: NOT LIKE much faster than LIKE?

Hi,

> I did just think of something we could improve though.  The pattern
> selectivity code doesn't make any use of the statistics about "most
> common values".  For a constant pattern, we could actually apply the
> pattern test with each common value and derive answers that are exact
> for the portion of the population represented by the most-common-values
> list.  If the MCV list covers a large fraction of the population then
> this would be a big leg up in accuracy.  Dunno if that applies to your
> particular case or not, but it seems worth doing ...

This reminds me what I did in a patch which is currently on hold for the 
next release:

http://momjian.postgresql.org/cgi-bin/pgpatches_hold
http://candle.pha.pa.us/mhonarc/patches_hold/msg00026.html

The patch was addressing a similar issue when using ltree <@ and @> 
operator on an unbalanced tree.


Best regards
--
Matteo Beccati
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