title: Flink: Default Partitioning/Shuffling Strategy/Functions
body: <p>Which strategies (hashing, sorting) does Flink use for reducing/grouping of DataSets (e.g. groupBy or reduce functions) by default? And which API-functions does Flink use for</p>
  
  <ol>
  <li>partitioning during the shuffle-step and </li>
  <li>sorting the elements within a partition </li>
  </ol>
  
  <p>by default?</p>