Collection<TraceIdTimestamp> traceIdTimestampsByServiceName(String serviceName) {
    List<TraceIdTimestamp> traceIdTimestamps = new ArrayList<>();
    for (String lowTraceId : serviceToTraceIds.get(serviceName)) {
      traceIdTimestamps.addAll(traceIdToTraceIdTimestamps.get(lowTraceId));
    }
    traceIdTimestamps.sort(TIMESTAMP_DESCENDING);
    return traceIdTimestamps;
  }
Returns service names orphaned by removing the trace ID
zipkin/src/main/java/zipkin2/storage/InMemoryStorage.java