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

Tim Peters tim.one@comcast.net
Mon, 29 Apr 2002 18:17:37 -0400

[Guido, on adjusting gc threshold up or down depending on how much garbage each gc pass finds]

Should we worry about programs that don't create any cyclical garbage for a long time, and then suddenly start creating lots of it? The initial GC-free period may bump the threshold up very far, and then it will build up a significant pile of cyclical garbage before GC runs again.

Yes, when the past is a rotten predictor of the future, it's hard to predict the future better than rottenly. Countless megabytes of cyclic structures may be kept alive by a single reference too, so looking for a bump in deallocation rate isn't a cure-all either.

A practical compromise would be to allow thresholds to auto-adjust, but only within a fixed range. That would give Neil the opportunity to add more tuning knobs nobody understands . I'd set the default upper bound pretty high, like a few million excess allocations. Somebody creating oodles of cyclic trash after a long quiet period, and who can't afford to let the memory go unreclaimed, would have to learn to import gc and force the issue. The rest of us would enjoy less gc overhead with little potential for harm.

I'd also do auto-adjust by more than 25%; *2 and /2 are more like it. Programs don't ease their way into different memory behaviors, when it changes it's likely to be a sharp break.