Avoid OOM when resizing very large dictionaries. #24
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VSadov
commented
Jul 7, 2023
| // Size calculation: 2 words (K+V) per table entry, plus a handful. We | ||
| // guess at 32-bit pointers; 64-bit pointers screws up the size calc by | ||
| // 2x but does not screw up the heuristic very much. | ||
| int kBs4 = (((newsz << 1) + 4) << 3/*word to bytes*/) >> 12/*kBs4*/; |
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The bug was here. Left shifts could turn the large size estimate into 0, leading to allocating multiple candidates (since we assumed that would be cheap and fast).
The rest is just rationalizing and cleaning up this logic a bit.
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This mostly matters in corner cases when dealing with abnormally huge dictionaries.
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Minor fix.
There is a logic that prevents allocating too many candidate tables when resizing large dictionaries.
The logic had a flaw that would make it not work when the size is really really large. That could allow allocation of numerous huge candidates that would often result in OOM failure in a scenario which would otherwise be survivable.