Parallel stream operations are supposed to run faster than sequential operations.  Is this expection justified?  Or is is naive?  In this session we will explore when and under which circumstances parallel execution pays.  In order to understand the performance model of streams we will discuss certain internals of streams, for instance iterators and spliterators as well as reduction vs. accumulation algorithms.  The goal is to enable stream users to come up with an informed guess regarding the performance of parallel vs. sequential stream operations.