presto-main/src/main/java/io/prestosql/cost/CostCalculatorWithEstimatedExchanges.java/ExchangeCostEstimator/visitPlan
class ExchangeCostEstimator:        @Override
        protected LocalCostEstimate visitPlan(PlanNode node, Void context)
        {
            // TODO implement logic for other node types and return LocalCostEstimate.unknown() here (or throw)
            return LocalCostEstimate.zero();
        }