Github user rxin commented on a diff in the pull request: https://github.com/apache/spark/pull/11242#discussion_r59111476 --- Diff: core/src/main/scala/org/apache/spark/rdd/UnionRDD.scala --- @@ -62,8 +62,14 @@ class UnionRDD[T: ClassTag]( 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) rdds.par else rdds --- End diff -- just create a shared pool that can be used here. no user code wouldn't necessarily slow down the operation. just imagine somebody running the following: ```scala (1 to 1000).par.foreach(_ => Thread.sleep(100000000)) ``` suddenly nobody can use union anymore.
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