maropu commented on a change in pull request #29677:
URL: https://github.com/apache/spark/pull/29677#discussion_r496338261
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/EnsureRequirements.scala
##########
@@ -52,7 +52,10 @@ case class EnsureRequirements(conf: SQLConf) extends
Rule[SparkPlan] {
case (child, distribution) =>
val numPartitions = distribution.requiredNumPartitions
.getOrElse(conf.numShufflePartitions)
- ShuffleExchangeExec(distribution.createPartitioning(numPartitions),
child)
+ // Like optimizer.CollapseRepartition removes adjacent repartition
operations,
+ // adjacent repartitions performed by shuffle can be also removed.
+ val newChild = if (child.isInstanceOf[ShuffleExchangeExec])
child.children.head else child
Review comment:
To avoid the case @HyukjinKwon pointed out above, it seems we need to
check if `outputPartitioning` is the same for narrowing down this optimization
scope.
Btw, in my opinion, to avoid complicating the `EnsureRequirements` rule
more, it would be better to remove these kinds of redundant shuffles in a new
rule after `EnsureRequirements` like https://github.com/apache/spark/pull/27096.
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