title: Why is the number of partitions after groupBy 200? Why is this 200 not some other number?
body: <p>It's Spark 2.2.0-SNAPSHOT.</p>
  
  <p>Why is the number of partitions after <code>groupBy</code> transformation 200 in the following example?</p>
  
  <pre><code>scala&gt; spark.range(5).groupByKey(_ % 5).count.rdd.getNumPartitions
  res0: Int = 200
  </code></pre>
  
  <p>What's so special about <code>200</code>? Why not some other number like <code>1024</code>?</p>
  
  <p>I've been told about <a href="https://stackoverflow.com/q/31265927/1305344">Why does groupByKey operation have always 200 tasks?</a> that asks specifically about <code>groupByKey</code>, but the question is about the "mystery" behind picking <code>200</code> as the default not why there are 200 partitions by default.</p>