c21 commented on a change in pull request #32528:
URL: https://github.com/apache/spark/pull/32528#discussion_r631610541
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/joins/SortMergeJoinExec.scala
##########
@@ -424,8 +424,18 @@ case class SortMergeJoinExec(
// A list to hold all matched rows from buffered side.
val clsName = classOf[ExternalAppendOnlyUnsafeRowArray].getName
+ // Flag to only buffer first matched row, to avoid buffering unnecessary
rows.
+ val onlyBufferFirstMatchedRow = (joinType, condition) match {
+ case (LeftSemi, None) => true
+ case _ => false
+ }
+ val inMemoryThreshold =
+ if (onlyBufferFirstMatchedRow) {
Review comment:
Good call. Actually the non-code-gen path can also depend on this, so I
make it just a `val` now.
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