title: Spark write parquet not writing any files, only _SUCCESS
body: <p>The application includes</p>
  
  <pre><code>val stats = sqlContext.sql("select id, n from myTable")
  
  stats.write.parquet("myTable.parquet")
  </code></pre>
  
  <p>This creates dir <code>myTable.parquet</code> with no contents other than an empty <code>_SUCCESS</code> file, even that</p>
  
  <pre><code>stats.show  // illustration only here, original size motivates parquet use
  
  +-----+----+
  |  id |  n |
  +-----+----+
  |   a |  1 |
  |   b |  2 |
  +-----+----+
  
  stats.printSchema 
  
  root
   |-- id: string (nullable = true)
   |-- n: long (nullable = true)
  </code></pre>
  
  <p>How to make <code>write.parquet</code> to write the actual contents of the dataframe ? What is missing ?</p>
  
  <p><strong>Note</strong> This occurs also with <code>saveAsTextFile</code>.</p>