@Override
  public boolean isSame(OperatorDesc other) {
    if (getClass().getName().equals(other.getClass().getName())) {
      ReduceSinkDesc otherDesc = (ReduceSinkDesc) other;
      return ExprNodeDescUtils.isSame(getKeyCols(), otherDesc.getKeyCols()) &&
          ExprNodeDescUtils.isSame(getValueCols(), otherDesc.getValueCols()) &&
          ExprNodeDescUtils.isSame(getPartitionCols(), otherDesc.getPartitionCols()) &&
          getTag() == otherDesc.getTag() &&
          Objects.equals(getOrder(), otherDesc.getOrder()) &&
          getTopN() == otherDesc.getTopN() &&
          isAutoParallel() == otherDesc.isAutoParallel();
    }
    return false;
  }
Returns the null order in the key columns.

@return null, which means default for all key columns, or a String
        of the same length as key columns, that consists of only "a"
        (null first) and "z" (null last).
ql/src/java/org/apache/hadoop/hive/ql/plan/ReduceSinkDesc.java