终于搞清楚了：redis最多能放多少个

2^32大约42亿个，但官方只测试到了2.5亿个，一起来看一下官方文档

FAQ – Redis

What is the maximum number of keys a single Redis instance can hold? and what is 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.

理论上 Redis 可以处理多达 2^32 的 keys，并且在实际中进行了测试，每个实例至少存放了 2 亿 5 千万的 keys，我们正在测试一些较大的值。

Every hash, list, set, and sorted set, can hold 2^32 elements.

任何 list、set、和 sorted set 都可以放 2^32 个元素。

In other words your limit is likely the available memory in your system.

换句话说，Redis 的存储极限是系统中的可用内存值。