title: What is the meaning of partitionColumn, lowerBound, upperBound, numPartitions parameters?
body: <p>While fetching data from SQL Server via a JDBC connection in Spark, I found that I can set some parallelization parameters like <code>partitionColumn</code>, <code>lowerBound</code>, <code>upperBound</code>, and <code>numPartitions</code>. I have gone through <a href="http://spark.apache.org/docs/latest/sql-programming-guide.html#jdbc-to-other-databases" rel="noreferrer">spark documentation</a> but wasn't able to understand it.</p>
  
  <p>Can anyone explain me the meanings of these parameters?</p>