title: Why does groupByKey operation have always 200 tasks?
body: <p>Whenever I do a <code>groupByKey</code> on an RDD, it gets split up in 200 jobs, even if the original table is quite large, e.g. 2k partitions and tens of millions of rows.</p>
  
  <p>Moreover, the operation seems to get stuck on the last two tasks which take extremely long to compute.</p>
  
  <p>Why is it 200? How to increase it and will it help?</p>