@Override
  public Operator<? extends OperatorDesc> getReducer(MapWork mapWork) {
    if (getWork().getMapWork() == mapWork) {
      return getWork().getReduceWork() == null ? null : getWork().getReduceWork().getReducer();
    }
    return 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