zhengruifeng commented on a change in pull request #31468:
URL: https://github.com/apache/spark/pull/31468#discussion_r573433676
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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:
refer to
[CoalesceExec.doExecute](https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/basicPhysicalOperators.scala#L715),
I update the fix to directly return empty RDD with single partition if
`childRDD.getNumPartitions == 0`
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