maropu commented on a change in pull request #31468:
URL: https://github.com/apache/spark/pull/31468#discussion_r573392812
##########
File path: sql/core/src/main/scala/org/apache/spark/sql/execution/limit.scala
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@@ -52,16 +52,21 @@ case class CollectLimitExec(limit: Int, child: SparkPlan)
extends LimitExec {
SQLShuffleReadMetricsReporter.createShuffleReadMetrics(sparkContext)
override lazy val metrics = readMetrics ++ writeMetrics
protected override def doExecute(): RDD[InternalRow] = {
- val locallyLimited = child.execute().mapPartitionsInternal(_.take(limit))
- val shuffled = new ShuffledRowRDD(
- ShuffleExchangeExec.prepareShuffleDependency(
- locallyLimited,
- child.output,
- SinglePartition,
- serializer,
- writeMetrics),
- readMetrics)
- shuffled.mapPartitionsInternal(_.take(limit))
+ val childRDD = child.execute()
+ val singlePartitionRDD = if (childRDD.getNumPartitions != 1) {
Review comment:
nit: could you leave some comments about why we cannot strip the shuffle
if `childRDD.getNumPartitions == 0`?
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