title: SparkSQL: task taking hours for small input
body: <p>I am currently facing a strange issue with apache spark 2.1 (scala).
  I am running sparkSQL job, which hangs for more than 2 hours on a task:</p>
  
  <p><a href="https://i.stack.imgur.com/6ASqD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6ASqD.png" alt="enter image description here"></a></p>
  
  <p>The first two tasks take more than 2 hours to complete for 751 input records, which does not make any sense to me.</p>
  
  <p>Moreover, in the logs I can see:</p>
  
  <pre><code>18/07/16 14:34:43 INFO Executor: Running task 0.0 in stage 21.0 (TID 3974)
  18/07/16 14:34:43 INFO Executor: Finished task 0.0 in stage 21.0 (TID 3974). 16874 bytes result sent to driver
  18/07/16 14:34:43 INFO Executor: Finished task 136.0 in stage 21.0 (TID 3873). 18268 bytes result sent to driver
  18/07/16 16:44:42 INFO Executor: Finished task 196.0 in stage 21.0 (TID 3921). 17190 bytes result sent to driver
  18/07/16 16:44:43 INFO BlockManager: Removing RDD 7
  18/07/16 16:44:43 INFO BlockManager: Removing RDD 59
  </code></pre>
  
  <p>So it really seems like the executor is not doing anything.</p>
  
  <p>Did anyone face such an issue before or would someone have some insights on this?</p>