On Thu, Jan 12, 2012 at 9:57 PM, Guido van Rossum <gu...@python.org> wrote: > Hm... I started out as a big fan of the randomized hash, but thinking more > about it, I actually believe that the chances of some legitimate app having >>1000 collisions are way smaller than the chances that somebody's code will > break due to the variable hashing.
Python's dicts are designed to avoid hash conflicts by resizing and keeping the available slots bountiful. 1000 conflicts sounds like a number that couldn't be hit accidentally unless you had a single dict using a terabyte of RAM (i.e. if Titus Brown doesn't object, we're good). The hashes also look to exploit cache locality but that is very unlikely to get one thousand conflicts by chance. If you get that many there is an attack. > This is depending on how the counting is done (I didn't look at MAL's > patch), and assuming that increasing the hash table size will generally > reduce collisions if items collide but their hashes are different. The patch counts conflicts on an individual insert and not lifetime conflicts. Looks sane to me. > That said, even with collision counting I'd like a way to disable it without > changing the code, e.g. a flag or environment variable. Agreed. Paranoid people can turn the behavior off and if it ever were to become a problem in practice we could point people to a solution. -Jack _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
