Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/7948#discussion_r36272364
--- Diff:
core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSorterSpillMerger.java
---
@@ -47,11 +47,19 @@ public int compare(UnsafeSorterIterator left,
UnsafeSorterIterator right) {
priorityQueue = new PriorityQueue<UnsafeSorterIterator>(numSpills,
comparator);
}
- public void addSpill(UnsafeSorterIterator spillReader) throws
IOException {
+ /**
+ * Add an UnsafeSorterIterator to this merger
+ */
+ public void addSpillIfNotEmpty(UnsafeSorterIterator spillReader) throws
IOException {
if (spillReader.hasNext()) {
+ // We only add the spillReader to the priorityQueue if it is not
empty. We do this to
--- End diff --
Yep, makes sense. Putting empty spill writers violates an invariant that's
maintained by the `loadNext()` loop: if a spill reader is in the priority
queue, then `getBaseObject()`, `getBaseOffset()`, etc. point to a row that has
not been returned yet. We covered the maintenance of that invariant but didn't
establish it properly when there were empty spills. This change fixes that,
though.
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