为什么 Redlock 算法说“It tries to acquire the lock in all the N instances sequentially”

[JasonLaw]

在Distributed locks with Redis – Redis - The Redlock algorithm中，它说

It tries to acquire the lock in all the N instances sequentially, using the same key name and random value in all the instances. During step 2, when setting the lock in each instance, the client uses a timeout which is small compared to the total lock auto-release time in order to acquire it. For example if the auto-release time is 10 seconds, the timeout could be in the ~ 5-50 milliseconds range. This prevents the client from remaining blocked for a long time trying to talk with a Redis node which is down: if an instance is not available, we should try to talk with the next instance ASAP.

sequentially 是什么含义？为什么要 sequentially 呢？

然后在Distributed locks with Redis – Redis - Retry on failure中，它又说

When a client is unable to acquire the lock, it should try again after a random delay in order to try to desynchronize multiple clients trying to acquire the lock for the same resource at the same time (this may result in a split brain condition where nobody wins). Also the faster a client tries to acquire the lock in the majority of Redis instances, the smaller the window for a split brain condition (and the need for a retry), so ideally the client should try to send the SET commands to the N instances at the same time using multiplexing.

这不是互相矛盾吗？还是我哪里理解错了？

[lance6716]

一上来并发请求锁，在并发高的时候冲突会很大吧。重试的时候由于随机 delay 冲突就变小了

[yibo2018]

最近也在看，也不知道是不是英文，所以争议才会这么大。我也提供一个佐证楼主的证据
https://redis.io/topics/distlock#:~:text=In%20order%20to%20meet,each%20instance%20is%20similar).

In order to meet this requirement, the strategy to talk with the N Redis servers to reduce latency is definitely multiplexing (or poor man's multiplexing, which is, putting the socket in non-blocking mode, send all the commands, and read all the commands later, assuming that the RTT between the client and each instance is similar).

这里的 multiplexing 是不是也是同时发送的意思？而不是依次

[JasonLaw]

@yibo2018 #2 我也是这么理解的🤐