Re: POSIX regex performance bug in 7.3 Vs. 7.2

Sigh. It seems that somebody broke caching of compiled regexes,
so that your regex is recompiled each time it's used. I haven't
dug into the logic yet, but I think it must have been a mistake
in Thomas' change to make the regex cache be searched circularly:

2002-06-14 22:49 thomas

* src/backend/utils/adt/regexp.c: Search the existing regular
expression cache as a ring buffer. Will optimize the case for
repeated calls for the same expression, which seems to be the most
common case. Formerly, always searched from the first entry. May
want to look at the least-recently-used algorithm to make sure it
is identifying the right slots to reclaim. Seems silly to do math
when it seems that we could simply use an incrementing counter...

Considering that we now know that this is a factor-of-150 performance
hit, I wonder if this is a "must fix" for 7.3.2? We already wrapped
the tarball, but ...

regards, tom lane