apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/message/DatabaseMessageSender.java/DatabaseMessageSender/sendMessage
class DatabaseMessageSender:  @Override
  @Transactional
  public void sendMessage(String message, String channel) {
    logger.info("Sending message {} to channel {}", message, channel);
    if (!Objects.equals(channel, Topics.APOLLO_RELEASE_TOPIC)) {
      logger.warn("Channel {} not supported by DatabaseMessageSender!", channel);
      return;
    }

    Tracer.logEvent("Apollo.AdminService.ReleaseMessage", message);
    Transaction transaction = Tracer.newTransaction("Apollo.AdminService", "sendMessage");
    try {
      ReleaseMessage newMessage = releaseMessageRepository.save(new ReleaseMessage(message));
      toClean.offer(newMessage.getId());
      transaction.setStatus(Transaction.SUCCESS);
    } catch (Throwable ex) {
      logger.error("Sending message to database failed", ex);
      transaction.setStatus(ex);
      throw ex;
    } finally {
      transaction.complete();
    }
  }