Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/8038#discussion_r36684365
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/TungstenAggregationIterator.scala
---
@@ -426,6 +426,10 @@ class TungstenAggregationIterator(
case _ => false
}
+ // Note: we spill the sorter's contents immediately after creating it.
Therefore, we must
+ // insert something into the sorter here to ensure that we acquire at
least a page of memory.
+ // Otherwise, children operators may steal the window of opportunity
and starve our sorter.
+
--- End diff --
How about we explicitly say that `externalSorter.insertKV(firstKey,
buffer)` will trigger the page allocation?
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