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GH-3522: Optimize IntList.size() from O(slabs) to O(1) with running counter #3533

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GH-3522: Optimize IntList.size() from O(slabs) to O(1) with running counter #3533

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9 changes: 3 additions & 6 deletions parquet-column/src/main/java/org/apache/parquet/column/values/dictionary/IntList.java
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,7 @@ private void incrementPosition() {
// not be added
private int[] currentSlab;
private int currentSlabPos;
private int totalSize;

private void allocateSlab() {
currentSlab = new int[currentSlabSize];
Expand Down Expand Up @@ -129,6 +130,7 @@ public void add(int i) {

currentSlab[currentSlabPos] = i;
++currentSlabPos;
++totalSize;
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@Fokko Fokko May 6, 2026

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Looking at the code, totalSize will always be the same as currentSlabSize

}

/**
Expand All @@ -150,11 +152,6 @@ public IntIterator iterator() {
* @return the current size of the list
*/
public int size() {
int size = currentSlabPos;
for (int[] slab : slabs) {
size += slab.length;
}
Comment on lines -154 to -156
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@Fokko Fokko May 6, 2026

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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)


return size;
return totalSize;
}
}