title: Are spark dataframes distributed?
body: <p>I'm converting a batch operation to a spark job with the intention of running in in AWS EMR; the core of this job is a join between two reasonably large data sets.</p>
  
  <p>The core of the operation is a join:</p>
  
  <pre><code>table_1: loaded from json file_1
  table_2: loaded from parquet file_2
  joined_table = table_1.join(table_2)
     .map(some_data_transformations)
  
  store_it_off(joined_table)
  </code></pre>
  
  <p>From the google definitions, a dataFrame is a tabular structure, and an Rdd is distributed; however, I've seen other notes that dataFrames are implemented based on Rdds.  Are dataframes distributed? Are they distributed only after certain steps to parallelize them?</p>