title: Not able to write Data in Parquet File using Spark Structured Streaming
body: <p>I have a Spark Structured Streaming:</p>
  
  <pre><code>val df = spark
        .readStream
        .format("kafka")
        .option("kafka.bootstrap.servers", "localhost:9092")
        .option("startingOffsets", "earliest")
        .option("endingOffsets", "latest")
        .option("subscribe", "topic")
        .load()
  </code></pre>
  
  <p>I want to write data to FileSystem using DataStreamWriter,</p>
  
  <pre><code>val query = df
            .writeStream
            .outputMode("append")
            .format("parquet")
            .start("data")
  </code></pre>
  
  <p>But zero files are getting created in <code>data</code> folder. Only <code>_spark_metadata</code> is getting created.</p>
  
  <p>However, I can see the data on console when <code>format</code> is <code>console</code>:</p>
  
  <pre><code>val query = df
            .writeStream
            .outputMode("append")
            .format("console")
            .start()
  
  +--------------------+------------------+------------------+
  |                time|              col1|              col2|
  +--------------------+------------------+------------------+
  |49368-05-11 20:42...|0.9166470338147503|0.5576946794171861|
  +--------------------+------------------+------------------+
  </code></pre>
  
  <p>I cannot understand the reason behind it.</p>
  
  <p>Spark - 2.1.0</p>