Github user davies commented on a diff in the pull request: https://github.com/apache/spark/pull/11242#discussion_r59048405 --- 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) --- End diff -- Is it possible that listing in some data source is not thread safe?
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