@Override
    public boolean accept(Operator<?> s, Operator<?> t, OpEdge opEdge) {
      if (!traverseableEdgeTypes.contains(opEdge.getEdgeType())) {
        return true;
      }
      if (s instanceof ReduceSinkOperator) {
        ReduceSinkOperator rs = (ReduceSinkOperator) s;
        if (!ParallelEdgeFixer.colMappingInverseKeys(rs).isPresent()) {
          return true;
        }
      }
      return false;
    }
Orders TS operators in decreasing order by "weight".
ql/src/java/org/apache/hadoop/hive/ql/optimizer/SharedWorkOptimizer.java