分布式系统：保持不同节点之间的时间戳一致性(Distributed Systems: Keeping timestamp consistency between different nodes)

 上下文 
 
 我们有一个分配系统。 我们从其中一个系统发出事件，这些系统从另一个系统读取以生成报告。 
 
 逻辑顺序由以下事实确保：即使发射器系统具有N个节点，也存在下划线的有限状态机，这使得不可能同时发射一个聚合的事件。 这些事件标有时间戳。 N个节点不能总是在时间上同步。 
 
 我们非常关心时间戳，因为生成报告的下游系统总是需要时间戳，因为“报告人员”关心这类数据以检查事情是否正确。 
 
 问题 
 
 2节点可能有一点差异的事实让我们思考。 让我们想象下一个例子。 
 
 事件的逻辑顺序是这样的： 
 
 事件1 =>事件2 =>事件3 
 
 但在数据库中，我们可能会遇到这种情况： 
 
-------------------------------------------
|  Name   |  TimeStamp  |  Logical Order  |
-------------------------------------------
| Event 1 |      2      |        1        |
| Event 2 |      1      |        2        |
| Event 3 |      3      |        3        |
-------------------------------------------
 
 你有没有看到， 事件2在事件1之后是逻辑上发生的，但它们的时间戳无法同步。 
 
 好吧，这不会每2秒发生一次，但可能会发生，因为时间戳来自不同的节点。 从报告的角度来看，这是一个异常现象。 
 
 可能的解决方案 
 
 
 
 让报告人员意识到可能存在的问题。 我们无法拥有一个全球性的时间来源（NTP不是一个很好的解决方案，因为有一些好的理由）所以如果有很小的时间差异不是问题，那就意味着“这个事件发生在那个周围时间”。 
 
 
 确保时间戳一致性检查逻辑流中的下一个事件的时间戳不能小于上一个使它们等于的事件的时间戳。 这不是事实，但即使从非开发人员的角度来看，也保持流程一致。 
 
 
 你有关于这个主题的经验吗？ 

Context
 
We have a distrubuted system. We emit events from one of those systems which are read from another system for report generation.
 
Logical order is ensured by the fact that even if the emitter system has N nodes there is a finite state machine underlined which makes impossible to have concurrent emission of an event for one aggregate. These events are marked with a timestamp. N nodes could not always be on synch about the time.
 
We care so much about timestamp because the down-stream system which generates reports needs quite always a timestamp because "Reporting people" care about this kind data to check things are going the right way.
 
The problem
 
The fact 2 nodes could have a little discrepancy is making us thinking. Let's imagine the next example.
 
The logical order of the events is this:
 
Event 1 => Event 2 => Event 3
 
But in the Database we could have this situation:
 
-------------------------------------------
|  Name   |  TimeStamp  |  Logical Order  |
-------------------------------------------
| Event 1 |      2      |        1        |
| Event 2 |      1      |        2        |
| Event 3 |      3      |        3        |
-------------------------------------------
 
Has you can see, Event 2 is logically happened after the Event 1 but their timestamp could not be on synch.
 
Ok, this is not going to happen every 2 seconds but it could happen because the timestamp comes from different nodes. And from a Reporting point of view this is an anomaly.
 
Possible solutions
 
 
 
Make Reporting people aware of the possible problem. We are not able to have one global source of time (NTP is not a good solution for some good reasons) so if there are discrepancies of a very small amount of time is not a problem and it means that "this event is happened around that time".
 
 
Ensure timestamp consistency checking that the next event in the logical flow could not have a timestamp which is less that the previous event making them equals. This is not the truth but keeps the flow consistent even from a non developer point of view.
 
 
Have you got experiences on this topic?

原文：https://stackoverflow.com/questions/20160631