@Override
    public Object process(Node nd, Stack<Node> stack, NodeProcessorCtx ctx,
        Object... nodeOutputs) throws SemanticException {
      ColumnPrunerProcCtx cppCtx = (ColumnPrunerProcCtx) ctx;
      cppCtx.getPrunedColLists().put((Operator<? extends OperatorDesc>) nd,
          cppCtx.genColLists((Operator<? extends OperatorDesc>) nd));

      return null;
    }
The Default Node Processor for Column Pruning.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/ColumnPrunerProcFactory.java