Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/11242#discussion_r61979221
--- Diff: core/src/main/scala/org/apache/spark/rdd/UnionRDD.scala ---
@@ -56,14 +58,30 @@ private[spark] class UnionPartition[T: ClassTag](
}
}
+object UnionRDD {
+ private lazy val partitionEvalThreadPool = new ForkJoinPool(8)
+}
+
@DeveloperApi
class UnionRDD[T: ClassTag](
sc: SparkContext,
var rdds: Seq[RDD[T]])
extends RDD[T](sc, Nil) { // Nil since we implement getDependencies
+ // visible for testing
+ private[spark] val isPartitionEvalParallel: Boolean =
+ rdds.length > conf.getInt("spark.rdd.parallelListingThreshold", 10)
+
override def getPartitions: Array[Partition] = {
- val array = new Array[Partition](rdds.map(_.partitions.length).sum)
+ val parRDDs = if (isPartitionEvalParallel) {
+ val parArray = rdds.par
+ parArray.tasksupport = new
ForkJoinTaskSupport(UnionRDD.partitionEvalThreadPool)
+ parArray
+ } else {
+ rdds
+ }
+ // evaluating parRDDs.map(_.partitions) will execute in parallel and
cache partitions
--- End diff --
I don't think this comment adds any value. First of all it's not
necessarily true. Second if it's a parallel seq then that's just what Scala
does, no surprises there.
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