get_sort_keys
获取一个hashkey下的sortkey值
def get_sort_keys(self, hash_key,
max_kv_count=100,
max_kv_size=1000000,
timeout=0):
"""
Get multiple sort keys under hash_key.
:param hash_key: (str) which hash key used for this API.
:param max_kv_count: (int) max count of k-v pairs to be fetched. max_fetch_count <= 0 means no limit.
:param max_kv_size: (int) max total data size of k-v pairs to be fetched. max_fetch_size <= 0 means no limit.
:param timeout: (int) how long will the operation timeout in milliseconds.
if timeout > 0, it is a timeout value for current operation,
else the timeout value specified to create the instance will be used.
:return: (tuple<error_types.code.value, set>) (code, ks)
code: error_types.ERR_OK.value when data got succeed.
ks: <sort_key, ign> pairs in dict, ign will always be empty str.
"""