bpo-46675: Allow object value arrays and split key dictionaries larger than 16 #31191
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| Allow more than 16 items in a split dict before it is combined. The limit is | |||
| now 254. | |||
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At a slight increase in overhead for for small object dictionaries, and an extra word of memory for sizes 7-15, this PR allows split-key dicts and "virtual" object dicts for size > 16.
The benchmarks suggest that this is not an improvement, but looking a bit closely reveals a couple of things.
The logging benchmarks are significantly faster. The log record object has ~20 attributes, so this is an expected improvement.
The pickle benchmarks are significantly slower, I don't know why.
Overall, this may not make things faster, but it does remove a "sharp edge". Adding an extra attribute (from 16 to 17) should not reduce performance by a significant amount.
Why are quite a few of the benchmarks slower?
I don't know, but my hypothesis is that the larger dict-keys is slowing down lookup due to poorer locality.
We may need to revisit static analysis, to provide better hints for the initial size of the dict keys.
https://bugs.python.org/issue46675