[Python-Dev] Tuning Python dicts (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Sat Apr 10 22:40:26 CEST 2010

Reid Kleckner <rnk mit.edu> writes:

I think you're right about the number of collisions, though. CPython dicts use a pretty low load factor (2/3) to keep collision counts down. One of the major benefits cited in the paper is the ability to maintain performance in the face of higher load factors, so I may be able to bump up the load factor to save memory. This would increase collisions, but then that wouldn't matter, because resolving them would only require looking within two consecutive cache lines.

Why wouldn't it matter? Hash collisions still involve more CPU work, even though if you're not access memory a lot.

Antoine.

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