presto-main/src/main/java/io/prestosql/operator/MarkDistinctOperator.java/MarkDistinctOperator/duplicate
class MarkDistinctOperator:        @Override
        public OperatorFactory duplicate()
        {
            return new MarkDistinctOperatorFactory(operatorId, planNodeId, types.subList(0, types.size() - 1), markDistinctChannels, hashChannel, joinCompiler);
        }