title: What is the Difference in using FORCE, ENABLE, DISABLE keyword in PARALLEL QUERY/DML/DDL
body: <p>What is the difference in following statements</p>
  
  <pre><code>ALTER SESSION FORCE   PARALLEL QUERY;
  ALTER SESSION ENABLE  PARALLEL DDL;
  ALTER SESSION DISABLE PARALLEL DML;
  </code></pre>
  
  <p>Which one is more suggested for the optimization point of view. Initially, I was using DISABLE, later on  I tested with ENABLE which performed better and now FORCE is doing better. Is there any chance that FORCE will backfire in any case.</p>