title: how to restrict the concurrent running map tasks?
body: <p>My hadoop version is 1.0.2. Now I want at most 10 map tasks running at the same time. I have found 2 variable related to this question.</p>
  
  <p>a) mapred.job.map.capacity</p>
  
  <p>but in my hadoop version, this parameter seems abandoned.</p>
  
  <p>b) mapred.jobtracker.taskScheduler.maxRunningTasksPerJob (http://grepcode.com/file/repo1.maven.org/maven2/com.ning/metrics.collector/1.0.2/mapred-default.xml)</p>
  
  <p>I set this variable like below:</p>
  
  <pre><code>Configuration conf = new Configuration();
  conf.set("date", date);
  conf.set("mapred.job.queue.name", "hadoop");
  conf.set("mapred.jobtracker.taskScheduler.maxRunningTasksPerJob", "10");
  
  DistributedCache.createSymlink(conf);
  Job job = new Job(conf, "ConstructApkDownload_" + date);
  ...
  </code></pre>
  
  <p>The problem is that it doesn't work. There is still more than 50 maps running as the job starts.</p>
  
  <p>After looking through the hadoop document, I can't find another to limit the concurrent running map tasks.
  Hope someone can help me ,Thanks.</p>
  
  <p>=====================</p>
  
  <p>I hava found the answer about this question, here share to others who may be interested.</p>
  
  <p>Using the fair scheduler, with configuration parameter maxMaps to set the a pool's maximum concurrent task slots, in the Allocation File (fair-scheduler.xml).
  Then when you submit jobs, just set the job's queue to the according pool.</p>