title: Can I index a column in parquet file to make it join faster using Spark
body: <p>I have two DataFrames each saved in a parquet file. I need to join this two DFs by the unique incremental "id" column.
  Can I created index on the id column so they can join faster? Here is the code</p>
  
  <pre><code>// First DF which contain a few thousands items
  val dfExamples = sqlContext.parquetFile("file:///c:/temp/docVectors.parquet")
  // Second DF which contains 10 million items
  val dfDocVectors = sqlContext.parquetFile(docVectorsParquet) // DataFrame of (id, vector)
  
  dfExamples.join(dfDocVectors, dfExamples("id") === dfDocVectors("id")).select(dfDocVectors("id"),
  dfDocVectors("vector"), dfExamples("cat"))
  </code></pre>
  
  <p>I need to perform such kind of join many times. To speed up the join, can I create index on
  the "id" column in the parquet file like what I can do to a database table?</p>