GH-3522: Optimize IntList.size() from O(slabs) to O(1) with running counter#3533
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iemejia wants to merge 1 commit intoapache:masterfrom
Open
GH-3522: Optimize IntList.size() from O(slabs) to O(1) with running counter#3533iemejia wants to merge 1 commit intoapache:masterfrom
iemejia wants to merge 1 commit intoapache:masterfrom
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…ning counter IntList.size() was iterating over all slabs to sum their lengths on every call. Replace with a simple totalSize counter incremented on each add(). This eliminates O(slabs) overhead from dictionary encoding hot paths where size() is called frequently.
Fokko
reviewed
May 6, 2026
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| private void allocateSlab() { | ||
| currentSlab = new int[currentSlabSize]; | ||
| currentSlabPos = 0; |
Contributor
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Should we also set totalSize to 0 here?
Fokko
reviewed
May 6, 2026
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| currentSlab[currentSlabPos] = i; | ||
| ++currentSlabPos; | ||
| ++totalSize; |
Contributor
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Looking at the code, totalSize will always be the same as currentSlabSize
Fokko
reviewed
May 6, 2026
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| for (int[] slab : slabs) { | ||
| size += slab.length; | ||
| } |
Contributor
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I don't think this change is correct. We're returning the slab length, and this one can grow as well (double until MAX_SLAB_SIZE)
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Summary
IntList.size()slab-iteration with a simpletotalSizecounter incremented on eachadd()size()is called frequentlyDetails
IntList.size()was iterating over all slabs to sum their lengths on every call. For delta encoding writers that check size thresholds frequently, this becomes O(slabs) per check. With a running counter it's O(1).The improvement is primarily relevant for large row groups where the number of slabs grows.
All 576 parquet-column tests pass.