title: Number reduce tasks Spark
body: <p>What is the formula that Spark uses to calculate the number of reduce tasks? </p>
  
  <p>I am running a couple of spark-sql queries and the number of reduce tasks always is 200. The number of map tasks for these queries is 154. I am on Spark 1.4.1.</p>
  
  <p>Is this related to spark.shuffle.sort.bypassMergeThreshold, which defaults to 200</p>