We all know the following fact:

1, RDD are immutable

2, Never modify RDD in place

3, Transform RDD to another RDD

There are 2 different transformations for RDD, one is narrow transformation:

transformations like map, flatMap, filter all are narrow transformation, which means shuffle won‘t happen, so it‘s fast, it‘s speed just depends on:

1, availability of local memory

2, CPU speed

another is wide transfomration:

transformations like groupByKey, reduceByKey, repartition all are wide tranformation, the network speed in shuffle is the key to it‘s speed, so it‘s slower

the final comparison:

Spark Transformations