ekoifman commented on a change in pull request #34464:
URL: https://github.com/apache/spark/pull/34464#discussion_r741555797



##########
File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/DynamicJoinSelection.scala
##########
@@ -50,10 +51,16 @@ object DynamicJoinSelection extends Rule[LogicalPlan] {
       mapStats.bytesByPartitionId.forall(_ <= 
maxShuffledHashJoinLocalMapThreshold)
   }
 
-  private def selectJoinStrategy(plan: LogicalPlan): Option[JoinStrategyHint] 
= plan match {
+  private def selectJoinStrategy(plan: LogicalPlan,
+                                 joinType: JoinType): Option[JoinStrategyHint] 
= plan match {
     case LogicalQueryStage(_, stage: ShuffleQueryStageExec) if 
stage.isMaterialized
       && stage.mapStats.isDefined =>
-      val demoteBroadcastHash = 
shouldDemoteBroadcastHashJoin(stage.mapStats.get)
+      val demoteBroadcastHash = joinType match {
+        // doesn't make sense for outer joins since one side is preserved and 
join is not
+        // short circuited if the other side is empty
+        case Inner | LeftSemi | LeftAnti => shouldDemoteBroadcastHashJoin 
(stage.mapStats.get)

Review comment:
       changed it a bit - seems more natural




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