官方說單例能處理key：2.5億個，參考鏈接:https://redis.io/topics/faq，以下是原話：
What is the maximum number of keys a single Redis instance can hold? and what the max number of elements in a Hash, List, Set, Sorted Set? Redis can handle up to 2^32 keys, and was tested in practice to handle at least 250 million keys per instance. Every hash, list, set, and sorted set, can hold 2^32 elements. In other words your limit is likely the available memory in your system.