Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/10451#discussion_r48392104 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala --- @@ -153,6 +153,15 @@ object SetOperationPushDown extends Rule[LogicalPlan] with PredicateHelper { ) ) + // Push down limit into union + case Limit(exp, Union(left, right)) => + Limit(exp, + Union( + CombineLimits(Limit(exp, left)), + CombineLimits(Limit(exp, right)) + ) + ) --- End diff -- Since we call `CombineLimits` here, we will not add extra `Limit` in the second iteration. Thus, I think it will cause the plan change. Thus, it will stop automatically, right?
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