original RDD to batch, not transient because it is used in compute method
previous batch that this RDD needs to wait before starting computation
set/batch of original RDD partitions that this RDD needs to evaluate
Get entire graph of depedencies for this batch RDD, for example original ← RDD1 ← RDD2 ← RDD3 will result in Seq(RDD1, RDD2) for RDD3 and empty sequence for RDD1.
original RDD to batch, not transient because it is used in compute method
previous batch that this RDD needs to wait before starting computation
MapRDD is a map-side RDD to serialize partition data, and wait for all parent RDDs to finish. Note that type 'T' must be serializable.