title: reuse JVM in Hadoop mapreduce jobs
body: <p>I know we can set the property "mapred.job.reuse.jvm.num.tasks" to re-use JVM. My questions are:</p>
  
  <p>(1) how to decide the number of tasks to be set here, -1 or some other positive integers?</p>
  
  <p>(2) is it a good idea to already reuse JVMs and set this property to the value of -1 in mapreduce jobs?</p>
  
  <p>Thank you very much!</p>