presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/GraphvizPrinter/getColumns
class GraphvizPrinter:        private static String getColumns(OutputNode node)
        {
            Iterator<String> columnNames = node.getColumnNames().iterator();
            String columns = "";
            int nameWidth = 0;
            while (columnNames.hasNext()) {
                String columnName = columnNames.next();
                columns += columnName;
                nameWidth += columnName.length();
                if (columnNames.hasNext()) {
                    columns += ", ";
                }
                if (nameWidth >= MAX_NAME_WIDTH) {
                    columns += "\\n";
                    nameWidth = 0;
                }
            }
            return columns;
        }