Re: POSIX regex performance bug in 7.3 Vs. 7.2

Neil Conway <neilc(at)samurai(dot)com> writes:
> Speaking of which, is there (or should there be) some mechanism for
> increasing the size of the compiled pattern cache? Perhaps a GUC var?

I thought about that while I was messing with the code, but I don't
think there's much point in it, unless someone wants to invest the work
to make the cache search much smarter (maybe a hash table?). At present
a larger cache will cost you in extra search time, especially in the
case where the pattern isn't in the cache.

I did do the work last night to convert the cache management algorithm
into a self-organizing list (a la Knuth) rather than a round-robin
search as it was before. This should reduce the expected number of
comparisons for cases where the cache is actually accomplishing
something, but of course it's no help if you have too many patterns
for the cache.

regards, tom lane