code: public List<Long> listBatchIds(ClientIdentity clientIdentity) throws CanalServerException {
          checkStart(clientIdentity.getDestination());
          checkSubscribe(clientIdentity);
  
          CanalInstance canalInstance = canalInstances.get(clientIdentity.getDestination());
          Map<Long, PositionRange> batchs = canalInstance.getMetaManager().listAllBatchs(clientIdentity);
          List<Long> result = new ArrayList<Long>(batchs.keySet());
          Collections.sort(result);
          return result;
      }
docs: 查询当前未被ack的batch列表，batchId会按照从小到大进行返回