@Override
  public void updateTaskMetrics(Metrics metrics) {
    metrics.incrementCounter(MetricsConstant.HIVE_MR_TASKS);
  }
Extension of ExecDriver:
- can optionally spawn a map-reduce task from a separate jvm
- will make last minute adjustments to map-reduce job parameters, viz:
  * estimating number of reducers
  * estimating whether job should run locally
ql/src/java/org/apache/hadoop/hive/ql/exec/mr/MapRedTask.java