title: How does Spark partition's HDFS files?
body: <p>If we have an uncompressed 320 blocks of HDFS files stored on a 16 data node cluster. Each node with 20 blocks and if we use Spark to read this file into an RDD (without explicitly passing <em>numPartitions</em> when creating an RDD)
  <code>textFile = sc.textFile("hdfs://input/war-and-peace.txt")</code></p>
  
  <p>If we have 16 executors one on each node, how many partitions Spark RDD will create per executor? Will it create one partition per HDFS block i.e. 20 partitions?</p>