private static boolean isStrictEqualityNeeded(ReduceSinkOperator cRS, ReduceSinkOperator pRS) {
    Operator<? extends OperatorDesc> parent = cRS.getParentOperators().get(0);
    while (parent != pRS) {
      assert parent.getNumParent() == 1;
      if (parent instanceof PTFOperator) {
        return true;
      }
      parent = parent.getParentOperators().get(0);
    }
    return false;
  }
Returns merge directions between two RSs for criterias (ordering, number of reducers,
reducer keys, partition keys). Returns null if any of categories is not mergeable.

Values for each index can be -1, 0, 1
1. 0 means two configuration in the category is the same
2. for -1, configuration of parent RS is more specific than child RS
3. for 1, configuration of child RS is more specific than parent RS
ql/src/java/org/apache/hadoop/hive/ql/optimizer/correlation/ReduceSinkDeDuplicationUtils.java