Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/7904#discussion_r36254811
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/joins/SortMergeJoin.scala
---
@@ -61,6 +61,7 @@ case class SortMergeJoin(
keys.map(SortOrder(_, Ascending))
protected override def doExecute(): RDD[InternalRow] = {
+ // TODO(josh): why is this copying necessary?
val leftResults = left.execute().map(_.copy())
--- End diff --
I noticed that SortMergeJoin has this defensive copying on both inputs. I
think that this is overly-conservative: we should only need to copy UnsafeRows
rows that might be buffered and we should be able to perform that copying at
the last possible moment when inserting the rows into the buffers. This means
that the stream side of a left or right outer join should not need to be copied.
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