This is a follow up to SPARK-2521 and should close SPARK-2546 (provided the implementation does not use shared conf objects). We no longer need to specially broadcast the Hadoop configuration since we are broadcasting RDD data anyways.
Remove all unnecessary broadcasts
UnionRDD's UnionPartition should not reference parent RDDs
Configuration object thread safety issue
[Github] Pull Request #1648 (rxin)
[Github] Pull Request #2683 (JoshRosen)
[Github] Pull Request #2935 (davies)