Time for action – killing a TaskTracker process

We've abused HDFS and its DataNode enough; now let's see what damage we can do to MapReduce by killing some TaskTracker processes.

Though there is an mradmin command, it does not give the sort of status reports we are used to with HDFS. So we'll use the MapReduce web UI (located by default on port 50070 on the JobTracker host) to monitor the MapReduce cluster health.

Perform the following steps:

1. Ensure everything is running via the start-all.sh script then point your browser at the MapReduce web UI. The page should look like the following screenshot:

   

2. Start a long-running MapReduce job; the example pi estimator with large values is great for this:

   $ Hadoop jar Hadoop/Hadoop-examples-1.0.4.jar pi 2500 2500
   

3. Now log onto a cluster node and use jps to identify the TaskTracker process:

   $ jps
   21822 TaskTracker
   3918 Jps
   3891 DataNode
   

4. Kill the TaskTracker process:

   $ kill -9 21822
   

5. Verify that the TaskTracker is no longer running:

   $jps
   3918 Jps
   3891 DataNode...