@Override
  public Operator<? extends OperatorDesc> getReducer(MapWork mapWork) {
    List<BaseWork> children = getWork().getChildren(mapWork);
    if (children.size() != 1) {
      return null;
    }

    if (!(children.get(0) instanceof ReduceWork)) {
      return null;
    }

    return ((ReduceWork)children.get(0)).getReducer();
  }
Close DagClient, log warning if it throws any exception.
We don't want to fail query if that function fails.
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/TezTask.java