In the previous section, we explored various RDD transformations that resulted in another RDD, however, an RDD operation that triggers Job computation and returns a non RDD value(s) is called an action. All the various transformations discussed previously do not get evaluated until an action gets called. Different transformations only help in materializing the lazily evaluated DAGs. It is the only action that triggers the data to be loaded in RDDs, transformation to be computed, and the final result to be either sent to the Driver program or written to a filesystem.
Some of the common actions widely used in Spark are discussed as follows:
