The tokenlimit with redis may work incorrectly due to network latency

[hrzq19901209]

Redis may get a lua cmd which generated a few seconds ago, this may make token increase incorrectly. 因为网络延迟以及reids排队处理命令，redis可能处理一个几秒前lua脚本，这会导致桶中的令牌出现非预期的增长。 比如令牌的增加速率是5/s,桶的大小是5，一次取一个令牌。（now、KEYS[2]对应lua脚本的内容） now：1712918331 令牌数：5 拿到令牌 KEYS[2]:1712918331 now：1712918331 令牌数：4 拿到令牌 KEYS[2]:1712918331 now：1712918331 令牌数：3 拿到令牌 KEYS[2]:1712918331 now：1712918331 令牌数：2 拿到令牌 KEYS[2]:1712918331 now：1712918331 令牌数：1 拿到令牌 KEYS[2]:1712918331

now：1712918332 令牌数：5 拿到令牌 KEYS[2]:1712918332 now：1712918332 令牌数：4 拿到令牌 KEYS[2]:1712918332 now：1712918332 令牌数：3 拿到令牌 KEYS[2]:1712918332 now：1712918332 令牌数：2 拿到令牌 KEYS[2]:1712918332

now：1712918331 令牌数：1 拿到令牌 KEYS[2]:1712918331 因为网络延迟导致redis现在才处理该命令，处理完后，KEYS[2]的值前移至1712918331，下次请求token时桶中的令牌数将增加5个

now：1712918332 令牌数：5 拿到令牌 KEYS[2]:1712918332 这里理应是拿不到令牌，1712918332该时段的令牌已经被拿完了 now：1712918332 令牌数：4 拿到令牌 KEYS[2]:1712918332 now：1712918332 令牌数：3 拿到令牌 KEYS[2]:1712918332 now：1712918332 令牌数：2 拿到令牌 KEYS[2]:1712918332 now：1712918332 令牌数：1 拿到令牌 KEYS[2]:1712918332

从业务角度看，1712918332这个时间段将处理9次请求，限流没生效

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Redis may get a lua cmd which generated a few seconds ago, this may make token increase incorrectly. Because of network delays and reids queuing commands, redis may process a Lua script several seconds ago, which will cause unexpected growth of tokens in the bucket. For example, the token increase rate is 5/s, the bucket size is 5, and one token is removed at a time. (now, KEYS[2] correspond to the content of the lua script) now: 1712918331 Number of tokens: 5 Get token KEYS[2]:1712918331 now: 1712918331 Number of tokens: 4 Get token KEYS[2]:1712918331 now: 1712918331 Number of tokens: 3 Get token KEYS[2]:1712918331 now: 1712918331 Number of tokens: 2 Get token KEYS[2]:1712918331 now: 1712918331 Number of tokens: 1 Get token KEYS[2]:1712918331

now: 1712918332 Number of tokens: 5 Get token KEYS[2]:1712918332 now: 1712918332 Number of tokens: 4 Get token KEYS[2]:1712918332 now: 1712918332 Number of tokens: 3 Get token KEYS[2]:1712918332 now: 1712918332 Number of tokens: 2 Get token KEYS[2]:1712918332

now: 1712918331 Number of tokens: 1 Get the token KEYS[2]:1712918331 Because of the network delay, redis is only processing the command now. After processing, the value of KEYS[2] is moved forward to 1712918331, and the next time the token is requested, the bucket The number of tokens in will be increased by 5

now: 1712918332 Number of tokens: 5 Get the token KEYS[2]:1712918332 You should not be able to get the token here. 1712918332 The tokens for this period have been taken. now: 1712918332 Number of tokens: 4 Get token KEYS[2]:1712918332 now: 1712918332 Number of tokens: 3 Get token KEYS[2]:1712918332 now: 1712918332 Number of tokens: 2 Get token KEYS[2]:1712918332 now: 1712918332 Number of tokens: 1 Get token KEYS[2]:1712918332

From a business perspective, 9 requests will be processed during this time period of 1712918332, and the current limit does not take effect.

[kevwan]

Thanks for submitting the issue! Any idea on the solution?

[Lansongxx]

@kevwan I think you just need to determine if now is greater than last_refreshed when updating last_refreshed, and only update it if it is. If you're okay with what I'm doing, I can submit a PR

[kevwan]

Would you please submit a PR that we can discuss on it?