title: Hadoop: number of available map slots based on cluster size
body: <p>Reading the syslog generated by Hadoop, I can see lines similar to this one..</p>
  
  <pre><code>2013-05-06 16:32:45,118 INFO org.apache.hadoop.mapred.JobClient (main): Setting default number of map tasks based on cluster size to : 84
  </code></pre>
  
  <p>Does anyone know how this value is computed?
  And how can I get this value in my program?</p>