Github user nongli commented on a diff in the pull request:
https://github.com/apache/spark/pull/10998#discussion_r51632943
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/TungstenAggregate.scala
---
@@ -426,14 +510,39 @@ case class TungstenAggregate(
ctx.updateColumn(buffer, dt, i, ev, updateExpr(i).nullable)
}
+ val countTerm = ctx.freshName("count")
+ ctx.addMutableState("int", countTerm, s"$countTerm = 0;")
+ val checkFallback = if (testFallbackStartsAt.isDefined) {
+ s"$countTerm < ${testFallbackStartsAt.get}"
+ } else {
+ "true"
+ }
+
+ // We try to do hash map based in-memory aggregation first. If there
is not enough memory (the
+ // hash map will return null for new key), we spill the hash map to
disk to free memory, then
+ // continue to do in-memory aggregation and spilling until all the
rows had been processed.
+ // Finally, sort the spilled aggregate buffers by key, and merge them
together for same key.
s"""
// generate grouping key
${keyCode.code}
- UnsafeRow $buffer =
$hashMapTerm.getAggregationBufferFromUnsafeRow($key);
+ UnsafeRow $buffer = null;
+ if ($checkFallback) {
--- End diff --
I don't get this. You seem to do a look up twice and line (539) . Is that
intentional?
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