docs: private void startFetch() {
      prepareConcurrentMultiGetTasks();
  
      // set the time of starting
      fetch_start_time = System.currentTimeMillis();
      if (LOG.isDebugEnabled()) {
        LOG.debug("Start to fetch data using multiget, there will be " + multi_get_wait_cnt
            + " multigets to call");
      }
  
      for (int con_idx = 0; con_idx < concurrency_multi_get; ++con_idx) {
        final List<MultiGetTask> con_mul_get_tasks = multi_get_tasks.get(con_idx);
        final int task_index = multi_get_indexs.get(con_idx).incrementAndGet();
  
        if (task_index < con_mul_get_tasks.size()) {
          final MultiGetTask task = con_mul_get_tasks.get(task_index);
          final MulGetCB mgcb = new MulGetCB(con_idx, task.getTSUIDs(), task.getGets());
          mgcb.fetch();
        }
      } // end for
    }