title: Is it possible for multiple Executors to be launched within a single Spark worker for one Spark Application?
body: <p>We are experiencing more cores running than anticipated by the SPARK_WORKER_CORES (set to one). As part of tracking this down let us consider a couple of the spark components and their descriptions in the docs:</p>
  
  <ul>
  <li><p><strong>Worker node</strong>  Any node that can run application code in the cluster</p></li>
  <li><p><strong>Executor</strong> A process launched for an application on a worker node, that runs tasks and keeps data in memory or disk storage across them. Each application <strong><em>has its own executors.</em></strong></p></li>
  </ul>
  
  <p>So - for that last sentence: can there be multiple executors on a given worker node for a single application? Or only one?</p>