雪花id的时钟回退问题

雪花id的时钟回退问题

September 27, 2023
Snowflake, Time
Mark

雪花id由64位二进制组成，转成字符串则长为19. 它依赖于系统时钟，如果出现时钟回退，会导致已经在用的id再次被生成。

怎么办呢？

  1. 记录上次生成时间，在本次生成时比较时间，如果当前时间比上次生成时间要小，则认为时钟回拨，直接报错。也可以一直重试，直到当前时间不小于上次生成时间。

  2. 采用历史时间则天然的不存在时间回拨问题。但是在超高并发情况下，历史的时间很快用完，时间一直保持在最新时间的话，这个时候还是会出现时间回拨。

  3. Go1.9开始，使用单调时钟: time.Now(), time.Since(), time.Until().

// # Monotonic Clocks

//

// Operating systems provide both a “wall clock,” which is subject to

// changes for clock synchronization, and a “monotonic clock,” which is

// not. The general rule is that the wall clock is for telling time and

// the monotonic clock is for measuring time. Rather than split the API,

// in this package the Time returned by time.Now contains both a wall

// clock reading and a monotonic clock reading; later time-telling

// operations use the wall clock reading, but later time-measuring

// operations, specifically comparisons and subtractions, use the

// monotonic clock reading.

//

// For example, this code always computes a positive elapsed time of

// approximately 20 milliseconds, even if the wall clock is changed during

// the operation being timed:

//

// start := time.Now()

// … operation that takes 20 milliseconds …

// t := time.Now()

// elapsed := t.Sub(start)

//

// Other idioms, such as time.Since(start), time.Until(deadline), and

// time.Now().Before(deadline), are similarly robust against wall clock

// resets.

R1

R2