// The dispatcher fires the processor corresponding to the closest matching
// rule and passes the context along
Dispatcher disp = new DefaultRuleDispatcher(getDefault(), opRules, new MapJoinWalkerCtx(
listMapJoinOpsNoRed, pGraphContext));
GraphWalker ogw = new GenMapRedWalker(disp);
ArrayList<Node> topNodes = new ArrayList<Node>();
topNodes.addAll(listMapJoinOps);
ogw.startWalking(topNodes, null);
pGraphContext.setListMapJoinOpsNoReducer(listMapJoinOpsNoRed);
return pGraphContext;
}