On Wed, Oct 13, 2010 at 10:51 AM, Tom Lane <[email protected]> wrote: > Alvaro Herrera <[email protected]> writes: >> Excerpts from Tom Lane's message of mié oct 13 10:32:36 -0300 2010: >>> Robert Haas <[email protected]> writes: >>>> I spent some time hacking on this. It doesn't appear to be too easy >>>> to get levenshtein_less_equal() working without slowing down plain old >>>> levenshtein() by about 6%. >>> >>> Is that really enough slowdown to be worth contorting the code to avoid? >>> I've never heard of an application where the speed of this function was >>> the bottleneck. > >> What if it's used on a expression index on a large table? > > So? Expression indexes don't result in multiple evaluations of the > function. If anything, that context would probably be even less > sensitive to the function runtime than non-index use. > > But the main point is that 6% performance penalty in a non-core function > is well below my threshold of pain. If it were important enough to care > about that kind of performance difference, it'd be in core. I'd rather > see us keeping the code simple, short, and maintainable.
Well, then you have to wonder whether it's worth having the lesss-than-or-equal-to version around at all. That's only about 2x faster on the same test case. I do think it's likely that people who call this function will call it many times, however - e.g. trying to find the closest matches from a dictionary for a given input string, so the worry about performance doesn't seem totally out of place. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
