title: Spark dataframe adding new column issue - Structured streaming
body: <p>I am using spark Structured streaming. I have a Dataframe and adding a new column  "current_ts".</p>
  
  <pre><code>inpuDF.withColumn("current_ts", lit(System.currentTimeMillis()))
  </code></pre>
  
  <p>This does not update every row with current epoch time. It updates the same epcoh time when the job was trigerred causing every row in DF to have the same values. This works well with normal spark jobs. Is this a issue with spark structured streaming ?</p>