title: Spark intersection implementation
body: <p>How does Spark implement intersection method? Does it require 2 RDDs to colocate on a single machine?</p>
  
  <p>From <a href="https://stackoverflow.com/questions/34542623/spark-intersection-is-taking-much-time">here</a> it says that it uses hashtables, which is a bit odd as it's probably not scalable and sorting both rdds and then comparing item by item might have provided a more scalable solution.</p>
  
  <p>Any thoughts on the subject are welcome</p>