[Python-Dev] iterzip() (original) (raw)

Guido van Rossum guido@python.org
Mon, 29 Apr 2002 19:56:36 -0400

The difficulty is with apps that grow a lot of long-lived containers that aren't trash and don't even contain cycles. There's no bound on how often they'll get crawled over looking for trash that ain't there, and the more of those you grow the longer it takes to look at them. When a gen2 collection doesn't find any trash, it should probably become less eager to try looking at the same stuff yet again. Adding more generations could have a similar good effect.

Half of a shadow of an idea: at least in my code, it's common to have gazillions of tuples, and they almost always contain just strings and numbers. Since they're immutable, they'll never contain anything else. So they could get unlinked from cyclic gc entirely without ill effect (it's not possible that they could ever be in a cycle). Perhaps a gen2 collection could learn something about this and automagically untrack them.

Different (complementary) idea: how about having more generations, each being traversed less frequently than the previous one? Maybe a (potentially) infinite number of generations? (Or at least a fixed limit that never gets reached in practice.) Wouldn't this have the same effect as increasing the threshold exponentially?

--Guido van Rossum (home page: http://www.python.org/~guido/)