presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/GraphvizPrinter/visitOutput
class GraphvizPrinter:        @Override
        public Void visitOutput(OutputNode node, Void context)
        {
            String columns = getColumns(node);
            printNode(node, format("Output[%s]", columns), NODE_COLORS.get(NodeType.OUTPUT));
            return node.getSource().accept(this, context);
        }