@Override
  public void shutdown() {
    super.shutdown();
    if (executor != null) {
      executor.destroy();
      executor = null;
    }
  }
Find out if a job can be run in local mode based on it's characteristics

@param conf Hive Configuration
@param numReducers total number of reducers for this job
@param inputLength the size of the input
@param inputFileCount the number of files of input
@return String null if job is eligible for local mode, reason otherwise
ql/src/java/org/apache/hadoop/hive/ql/exec/mr/MapRedTask.java