presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/NodePrinter/visitSort
class NodePrinter:        @Override
        public Void visitSort(SortNode node, Void context)
        {
            printNode(node, format("Sort[%s]", Joiner.on(", ").join(node.getOrderingScheme().getOrderBy())), NODE_COLORS.get(NodeType.SORT));
            return node.getSource().accept(this, context);
        }