async_multi_get_sortkeys

异步获取hashkey下面的多个sortkey（不包含value）

  1.     ///
  2.     /// \brief asynchronous multi_get_sortkeys
  3.     ///     get multiple sort keys by hash key from the cluster.
  4.     ///     only fetch sort keys, but not fetch values.
  5.     ///     will not be blocked, return immediately.
  6.     /// \param hashkey
  7.     /// used to decide which partition to get this k-v
  8.     /// \param callback
  9.     /// the callback function will be invoked after operation finished or error occurred.
  10.     /// \param max_fetch_count
  11.     /// max count of sort keys to be fetched. max_fetch_count <= 0 means no limit.
  12.     /// \param max_fetch_size
  13.     /// max size of sort keys to be fetched. max_fetch_size <= 0 means no limit.
  14.     /// \param timeout_milliseconds
  15.     /// if wait longer than this value, will return time out error
  16.     /// \return
  17.     /// void.
  18.     ///
  19.     virtual void async_multi_get_sortkeys(const std::string &hashkey,
  20.                                           async_multi_get_sortkeys_callback_t &&callback = nullptr,
  21.                                           int max_fetch_count = 100,
  22.                                           int max_fetch_size = 1000000,
  23.                                           int timeout_milliseconds = 5000) = 0;