spark repartition

https://jaceklaskowski.gitbooks.io/mastering-apache-spark/content/spark-rdd-partitions.html

http://stackoverflow.com/questions/31610971/spark-repartition-vs-coalesce

http://dev.sortable.com/spark-repartition/

http://spark.apache.org/docs/latest/programming-guide.html

https://spark.apache.org/docs/1.2.0/programming-guide.html

http://stackoverflow.com/questions/38249624/how-to-increase-partitions-of-the-sql-result-from-hivecontext-in-spark-sql/40703599#40703599

http://stackoverflow.com/questions/39368516/number-of-partitions-of-spark-dataframe

https://hackernoon.com/managing-spark-partitions-with-coalesce-and-repartition-4050c57ad5c4

https://stackoverflow.com/questions/35800795/number-of-partitions-in-rdd-and-performance-in-spark/35804407#35804407

http://spark.apache.org/docs/latest/tuning.html#level-of-parallelism