title: Apache Spark 3 and backward compatibility?
body: <p>We have several Spark applications running on production developed using Spark 2.4.1 (Scala 2.11.12).
  For couple of our new Spark jobs,we are considering utilizing features of DeltaLake.For this we need to use Spark 2.4.2 (or higher).</p>
  <p>My questions are:</p>
  <ol>
  <li>If we upgrade our Spark cluster to 3.0.0, can our 2.4.1 applications still run on the new cluster (without recompile)?</li>
  <li>If we need to recompile our previous Spark jobs with Spark 3, are they source compatible or do they need any migration?</li>
  </ol>