presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/EdgePrinter/EdgePrinter
class EdgePrinter:        public EdgePrinter(StringBuilder output, Map<PlanFragmentId, PlanFragment> fragmentsById, PlanNodeIdGenerator idGenerator)
        {
            this.output = output;
            this.fragmentsById = ImmutableMap.copyOf(fragmentsById);
            this.idGenerator = idGenerator;
        }