private DummyStoreOperator getJoinParentOp(Operator<?> mergeReduceOp) {
    for (Operator<?> childOp : mergeReduceOp.getChildOperators()) {
      if ((childOp.getChildOperators() == null) || (childOp.getChildOperators().isEmpty())) {
        if (childOp instanceof DummyStoreOperator) {
          return (DummyStoreOperator) childOp;
        } else {
          throw new IllegalStateException("Was expecting dummy store operator but found: " + childOp);
        }
      } else {
        return getJoinParentOp(childOp);
      }
    }
    throw new IllegalStateException("Expecting a DummyStoreOperator found op: " + mergeReduceOp);
  }
Get the inputs that should be streamed through reduce plan.

@param inputs
@return
@throws Exception
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/ReduceRecordProcessor.java