presto-main/src/main/java/io/prestosql/sql/planner/LocalExecutionPlanner.java/Visitor/visitExchange
class Visitor:        @Override
        public PhysicalOperation visitExchange(ExchangeNode node, LocalExecutionPlanContext context)
        {
            checkArgument(node.getScope() == LOCAL, "Only local exchanges are supported in the local planner");

            if (node.getOrderingScheme().isPresent()) {
                return createLocalMerge(node, context);
            }

            return createLocalExchange(node, context);
        }