Copilot commented on code in PR #17186:
URL: https://github.com/apache/pinot/pull/17186#discussion_r2517187574
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pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/creator/impl/stats/NoDictColumnStatisticsCollector.java:
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@@ -208,8 +222,12 @@ public int getMaxRowLengthInBytes() {
@Override
public int getCardinality() {
- // Get approximate distinct count estimate using HLL++
- // Increase by 10% to increase probability of not returning lower than
actual cardinality
+ // If we are still tracking exact uniques, return exact cardinality
+ Set<Object> exact = _exactUniquesRef.get(); // local snapshot to avoid
races
+ if (exact != null) {
+ return exact.size();
Review Comment:
The exact set can become null between the `get()` and `size()` calls due to
concurrent modification in `trackExactUnique()`. Although unlikely in practice
due to the timing window, this could result in a `NullPointerException`.
Consider using a local variable pattern with a null check after reading the set
reference.
```suggestion
// Defensive: exact can become null between get() and size() due to
concurrent modification
return exact != null ? exact.size() : (int)
Math.round(_hllPlus.cardinality() * 1.1);
```
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