multi_get
读取多条数据
///
/// \brief multi_get
/// get multiple value by key from the cluster.
/// \param hashkey
/// used to decide which partition to get this k-v
/// \param sortkeys
/// all the k-v under hashkey will be sorted by sortkey.
/// if empty, means fetch all sortkeys under the hashkey.
/// \param values
/// the returned <sortkey,value> pairs will be put into it.
/// if data is not found for some <hashkey,sortkey>, then it will not appear in the map.
/// \param max_fetch_count
/// max count of k-v pairs to be fetched. max_fetch_count <= 0 means no limit.
/// \param max_fetch_size
/// max size of k-v pairs to be fetched. max_fetch_size <= 0 means no limit.
/// \param timeout_milliseconds
/// if wait longer than this value, will return time out error
/// \return
/// int, the error indicates whether or not the operation is succeeded.
/// this error can be converted to a string using get_error_string().
/// returns PERR_OK if fetch done, even no data is returned.
/// returns PERR_INCOMPLETE is only partial data is fetched.
///
virtual int multi_get(const std::string &hashkey,
const std::set<std::string> &sortkeys,
std::map<std::string, std::string> &values,
int max_fetch_count = 100,
int max_fetch_size = 1000000,
int timeout_milliseconds = 5000,
internal_info *info = NULL) = 0;
注:max_fetch_count 和 max_fetch_size 分别从kv-pair的条数 和 总的大小来限制multi_get的返回值