@Override
    public Object process(Node nd, Stack<Node> stack, NodeProcessorCtx procCtx,
        Object... nodeOutputs) throws SemanticException {
      MapJoinWalkerCtx ctx = (MapJoinWalkerCtx) procCtx;
      AbstractMapJoinOperator<? extends MapJoinDesc> mapJoin = ctx.getCurrMapJoinOp();
      addRejectMapJoinToCtx(ctx, mapJoin);
      return null;
    }
Store the mapjoin in a rejected list.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/MapJoinProcessor.java