Added comments.

sarutak · sarutak · commit 0da9e8270e32 · 2020-09-08T22:04:03.000+09:00
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/EnsureRequirements.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/EnsureRequirements.scala
@@ -52,6 +52,8 @@ case class EnsureRequirements(conf: SQLConf) extends Rule[SparkPlan] {
       case (child, distribution) =>
         val numPartitions = distribution.requiredNumPartitions
           .getOrElse(conf.numShufflePartitions)
+        // 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
         ShuffleExchangeExec(distribution.createPartitioning(numPartitions), newChild)
     }

Original file line number	Diff line number	Diff line change
`@@ -52,6 +52,8 @@ case class EnsureRequirements(conf: SQLConf) extends Rule[SparkPlan] {`
`52`	`52`	`case (child, distribution) =>`
`53`	`53`	`val numPartitions = distribution.requiredNumPartitions`
`54`	`54`	`.getOrElse(conf.numShufflePartitions)`
	`55`	`+ // Like optimizer.CollapseRepartition removes adjacent repartition operations,`
	`56`	`+ // adjacent repartitions performed by shuffle can be also removed.`
`55`	`57`	`val newChild = if (child.isInstanceOf[ShuffleExchangeExec]) child.children.head else child`
`56`	`58`	`ShuffleExchangeExec(distribution.createPartitioning(numPartitions), newChild)`
`57`	`59`	`}`