presto-main/src/main/java/io/prestosql/sql/planner/planprinter/PlanPrinter.java/PlanPrinter/visitMarkDistinct
class PlanPrinter:        @Override
        public Void visitMarkDistinct(MarkDistinctNode node, Void context)
        {
            addNode(node,
                    "MarkDistinct",
                    format("[distinct=%s marker=%s]%s", formatOutputs(types, node.getDistinctSymbols()), node.getMarkerSymbol(), formatHash(node.getHashSymbol())));

            return processChildren(node, context);
        }