Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/8512#discussion_r43576761
--- Diff: core/src/main/scala/org/apache/spark/rdd/UnionRDD.scala ---
@@ -62,7 +66,23 @@ class UnionRDD[T: ClassTag](
var rdds: Seq[RDD[T]])
extends RDD[T](sc, Nil) { // Nil since we implement getDependencies
+ // Evaluate partitions in parallel. Partitions of each rdd will be
cached by the `partitions`
+ // val in `RDD`.
+ private lazy val evaluatePartitions: Unit = {
+ val threshold = conf.getInt("spark.rdd.parallelListingThreshold", 10)
+ Preconditions.checkArgument(threshold > 0,
+ "spark.rdd.parallelListingThreshold must be positive: %s",
threshold.toString)
+ if (rdds.length > threshold) {
+ val parArray = rdds.toParArray
+ parArray.tasksupport = new ForkJoinTaskSupport(new
ForkJoinPool(threshold))
+ parArray.foreach(_.partitions)
+ } else {
+ rdds.foreach(_.partitions)
+ }
+ }
+
--- End diff --
I am not very comfortable with this lazy val. It is not obvious what it is
doing and there is no way to disable it.
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