code: public synchronized List<SessionId> getLoggedSessions() {
      // TODO: Find a solution that can handle large numbers of sessions, maybe by
      // reading them from disc.
      ImmutableList.Builder<SessionId> builder = new ImmutableList.Builder<>();
      builder.addAll(perSessionDriverEntries.keySet());
      return builder.build();
    }
docs: Returns a list of session IDs for which there are logs.
  
  The type of logs that are available depends on the log types provided
  by the driver. An included session id will at least have server logs.
  
  @return The list of session IDs.