presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/NodePrinter/visitRemoteSource
class NodePrinter:        @Override
        public Void visitRemoteSource(RemoteSourceNode node, Void context)
        {
            printNode(node, (node.getOrderingScheme().isPresent() ? "Merge" : "Exchange") + " 1:N", NODE_COLORS.get(NodeType.EXCHANGE));
            return null;
        }