Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/14723#discussion_r75586622
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/interfaces.scala
---
@@ -389,3 +389,89 @@ abstract class DeclarativeAggregate
def right: AttributeReference =
inputAggBufferAttributes(aggBufferAttributes.indexOf(a))
}
}
+
+/**
+ * This traits allow user to define an AggregateFunction which can store
**arbitrary** Java objects
+ * in Aggregation buffer during aggregation of each key group. This trait
must be mixed with
+ * class ImperativeAggregate.
--- End diff --
I think at here, we need to emphasize that the buffer is an internal buffer
because we will emit this buffer as the result of an aggregate operator.
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