GraphWalker ogw = new PreOrderWalker(disp);
// Create a list of topop nodes
List<Node> topNodes = new ArrayList<Node>();
topNodes.addAll(pGraphContext.getTopOps().values());
ogw.startWalking(topNodes, null);
Map<ReduceSinkOperator, List<ExprNodeDesc>> newFilters = context.getNewfilters();
// insert new filter between RS and parent of RS
for (Map.Entry<ReduceSinkOperator, List<ExprNodeDesc>> entry : newFilters.entrySet()) {