Jim Jewett <jimjjew...@gmail.com> added the comment: To be more explicit about Martin A. Lemburg's msg151121 (which I agree with):
Count the collisions on a single lookup. If they exceed a threshhold, do something different. Martin's strawman proposal was threshhold=1000, and raise. It would be just as easy to say "whoa! 5 collisions -- time to use the alternative hash instead" (and, possibly, to issue a warning). Even that slight tuning removes the biggest objection, because it won't ever actually fail. Note that the use of a (presumably stronger 2nd) hash wouldn't come into play until (and unless) there was a problem for that specific key in that specific dictionary. For the normal case, nothing changes -- unless we take advantage of the existence of a 2nd hash to simplify the first few rounds of collision resolution. (Linear probing is more cache-friendly, but also more vulnerable to worst-case behavior -- but if probing stops at 4 or 8, that may not matter much.) For quick scripts, the 2nd hash will almost certainly never be needed, so startup won't pay the penalty. The only down side I see is that the 2nd (presumably randomized) hash won't be cached without another slot, which takes more memory and shouldn't be done in a bugfix release. ---------- nosy: +Jim.Jewett _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue13703> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
