private boolean nonSubqueryMapJoin(MapJoinOperator mapJoin, MapJoinOperator parentMapJoin) {
      if (mapJoin.getParentOperators().contains(parentMapJoin)) {
        return true;
      }
      return false;
    }
Store the current mapjoin in the context.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/MapJoinProcessor.java