Github user yhuai commented on a diff in the pull request: https://github.com/apache/spark/pull/5208#discussion_r28394950 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/Exchange.scala --- @@ -157,28 +205,61 @@ private[sql] case class AddExchange(sqlContext: SQLContext) extends Rule[SparkPl case Seq(a,b) => a compatibleWith b }.exists(!_) - // Check if the partitioning we want to ensure is the same as the child's output - // partitioning. If so, we do not need to add the Exchange operator. - def addExchangeIfNecessary(partitioning: Partitioning, child: SparkPlan): SparkPlan = - if (child.outputPartitioning != partitioning) Exchange(partitioning, child) else child + // Adds Exchange or Sort operators as required + def addOperatorsIfNecessary( + partitioning: Partitioning, + rowOrdering: Seq[SortOrder], + child: SparkPlan): SparkPlan = { + val needSort = rowOrdering.nonEmpty && child.outputOrdering != rowOrdering + val needsShuffle = child.outputPartitioning != partitioning + val canSortWithShuffle = Exchange.canSortWithShuffle(partitioning, rowOrdering) + + if (needSort && needsShuffle && canSortWithShuffle) { + Exchange(partitioning, rowOrdering, child) + } else { + val withShuffle = if (needsShuffle) { + Exchange(partitioning, Nil, child) + } else { + child + } - if (meetsRequirements && compatible) { + val withSort = if (needSort) { + Sort(rowOrdering, global = false, withShuffle) --- End diff -- Like what we do in `SparkStrategies`, use `execution.ExternalSort` when `sqlContext.conf.externalSortEnabled` is `true`.
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