Github user chenghao-intel commented on a diff in the pull request:
https://github.com/apache/spark/pull/8798#discussion_r39816093
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/TungstenAggregationIterator.scala
---
@@ -375,7 +377,11 @@ class TungstenAggregationIterator(
val buffer: UnsafeRow =
hashMap.getAggregationBufferFromUnsafeRow(groupingKey)
if (buffer == null) {
// buffer == null means that we could not allocate more memory.
--- End diff --
The root cause, we will switch to sort-based aggregation only we don't have
enough memory, however, the first step of sort-based aggregation is spill,
which also requires more memory to be allocated.
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