apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/message/DatabaseMessageSender.java/DatabaseMessageSender/DatabaseMessageSender
class DatabaseMessageSender:  public DatabaseMessageSender(final ReleaseMessageRepository releaseMessageRepository) {
    cleanExecutorService = Executors.newSingleThreadExecutor(ApolloThreadFactory.create("DatabaseMessageSender", true));
    cleanStopped = new AtomicBoolean(false);
    this.releaseMessageRepository = releaseMessageRepository;
  }