官方FAQ表示，因為Redis是基於內存的操作，CPU不是Redis的瓶頸，Redis的瓶頸最有可能是機器內存的大小或者網絡帶寬。既然單線程容易實現，而且CPU不會成為瓶頸，那就順理成章地采用單線程的方案了
Redis is single threaded. How can I exploit multiple CPU / cores?
It's not very frequent that CPU becomes your bottleneck with Redis, as usually Redis is either memory or network bound. For instance, using pipelining Redis running on an average Linux system can deliver even 1 million requests per second, so if your application mainly uses O(N) or O(log(N)) commands, it is hardly going to use too much CPU.
However, to maximize CPU usage you can start multiple instances of Redis in the same box and treat them as different servers. At some point a single box may not be enough anyway, so if you want to use multiple CPUs you can start thinking of some way to shard earlier.
You can find more information about using multiple Redis instances in the Partitioning page.
However with Redis 4.0 we started to make Redis more threaded. For now this is limited to deleting objects in the background, and to blocking commands implemented via Redis modules. For the next releases, the plan is to make Redis more and more threaded.
正是由於在單線程模式的情況下已經很快了，就沒有必要在使用多線程了！但是，我們使用單線程的方式是無法發揮多核CPU 性能，不過我們可以通過在單機開多個Redis 實例來完善！
警告1：這里我們一直在強調的單線程，只是在處理我們的網絡請求的時候只有一個線程來處理，一個正式的Redis Server運行的時候肯定是不止一個線程的，這里需要大家明確的注意一下！
警告2：在上圖中FAQ中的最后一段，表述了從Redis 4.0版本開始會支持多線程的方式，但是，只是在某一些操作上進行多線程的操作！所以該篇文章在以后的版本中是否還是單線程的方式需要讀者考證！
轉自：https://blog.csdn.net/xlgen157387/article/details/79470556