Github user dbtsai commented on a diff in the pull request:
https://github.com/apache/spark/pull/11242#discussion_r56747209
--- Diff: core/src/main/scala/org/apache/spark/rdd/UnionRDD.scala ---
@@ -62,7 +64,23 @@ 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[spark] lazy val parallelPartitionEval: Boolean = {
--- End diff --
I'm also curious to use the default thread pool, and I like the idea not
adding extra knobs to tune. However, in the case, should we still have a hard
coded default threshold since when the # of rdds are small, we don't want the
overhead.
If we just make `rdds.zipWithIndex` parallel, it will be hard to test if
this path is touched. What do you think?
Thanks.
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