Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/8512#discussion_r43440241
--- Diff: core/src/main/scala/org/apache/spark/rdd/UnionRDD.scala ---
@@ -62,7 +64,20 @@ class UnionRDD[T: ClassTag](
var rdds: Seq[RDD[T]])
extends RDD[T](sc, Nil) { // Nil since we implement getDependencies
+ // Evaluate partitions in parallel (will be cached in each rdd)
+ private lazy val evaluatePartitions: Unit = {
+ val threshold = conf.getInt("spark.rdd.parallelListingThreshold", 10)
+ if (rdds.length > threshold) {
+ val parArray = rdds.toParArray
+ parArray.tasksupport = new ForkJoinTaskSupport(new
ForkJoinPool(threshold))
--- End diff --
What will happen if `threshold =0` or `threshold =-1`?
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