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SPARK-4968: takeOrdered to skip reduce step in case mappers return no partitions #3830

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SPARK-4968: takeOrdered to skip reduce step in case mappers return no partitions #3830

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15 changes: 10 additions & 5 deletions core/src/main/scala/org/apache/spark/rdd/RDD.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1146,15 +1146,20 @@ abstract class RDD[T: ClassTag](
if (num == 0) {
Array.empty
} else {
mapPartitions { items =>
val mapRDDs = mapPartitions { items =>
// Priority keeps the largest elements, so let's reverse the ordering.
val queue = new BoundedPriorityQueue[T](num)(ord.reverse)
queue ++= util.collection.Utils.takeOrdered(items, num)(ord)
Iterator.single(queue)
}.reduce { (queue1, queue2) =>
queue1 ++= queue2
queue1
}.toArray.sorted(ord)
}
if (mapRDDs.partitions.size == 0) {
Array.empty
} else {
mapRDDs.reduce { (queue1, queue2) =>
queue1 ++= queue2
queue1
}.toArray.sorted(ord)
}
}
}

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