presto-main/src/main/java/io/prestosql/sql/planner/optimizations/AddLocalExchanges.java/Rewriter/visitEnforceSingleRow
class Rewriter:        @Override
        public PlanWithProperties visitEnforceSingleRow(EnforceSingleRowNode node, StreamPreferredProperties parentPreferences)
        {
            return planAndEnforceChildren(node, singleStream(), defaultParallelism(session));
        }