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0 pointsdelusional3y ago0 comments

b) You're asking for occasional "eventual consistency" trouble when A's state lags or has moved on ahead of the event

If you allow A's state to lag behind it's own events, then how are you ever going to create a sane system? Surely A either has to be ahead or at the state that caused the event to emit, or events are pointless.

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SideburnsOfDoom3y ago

> A's state to lag behind it's own events,

Real systems don't have just 2 services. There can be 100s and the "own events" assumption may not hold.

delusionalOP3y ago

Sure, but in a thin events model someone would "own" the events since otherwise the subscriber wouldn't know where to query the actual data. What would you even do with an event saying a customer changes address if querying that address then produces the old one.

I'm genuinely curious how such an architecture would work. You don't have to respond directly here, but if you have any reference to further reading, I'd appreciate it.

SideburnsOfDoom3y ago

> I'm genuinely curious how such an architecture would work.

Complex systems are the way that they are because they got that way over time. It is not my goal to defend or even characterise a system that I did not create.

I am here telling you the issue that I saw: one event consumer, at an edge case, ran substantially behind another, and when they attempted to co-ordinate over http, this failed. And how it was successfully resolved: fatter events removed the need for co-ordination between these two altogether. This was IMHO a more elegant design - it avoided he issues of the the thin events.

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tremon3y ago

If you allow A's state to lag behind it's own events

That's a mischaracterization. A's state is not lagging its emitted events; instead, A's state may have been changed at the time A's event is processed.

SideburnsOfDoom3y ago

The "own events" was the faulty assumption. it's not always the same service that both emits the events, and is the place to go to over http for data. It "seems logical" to also build that store from listening to events, but it can cause issues as mentioned.

delusionalOP3y ago

The comment I quoted says:

> when A's state lags or has moved on ahead of the event

That sounds like it can EITHER be ahead or behind. Specifically, I do not understand it as A's state can either lag OR be ahead, not that "lags" is a synonym for "moved ahead"

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SideburnsOfDoom3y ago

> A's state to lag behind it's own events,

Real systems don't have just 2 services. There can be 100s and the "own events" assumption may not hold.

delusionalOP3y ago

I'm genuinely curious how such an architecture would work. You don't have to respond directly here, but if you have any reference to further reading, I'd appreciate it.

SideburnsOfDoom3y ago

> I'm genuinely curious how such an architecture would work.

Complex systems are the way that they are because they got that way over time. It is not my goal to defend or even characterise a system that I did not create.

1 more reply

tremon3y ago

If you allow A's state to lag behind it's own events

That's a mischaracterization. A's state is not lagging its emitted events; instead, A's state may have been changed at the time A's event is processed.

SideburnsOfDoom3y ago

delusionalOP3y ago

The comment I quoted says:

> when A's state lags or has moved on ahead of the event

That sounds like it can EITHER be ahead or behind. Specifically, I do not understand it as A's state can either lag OR be ahead, not that "lags" is a synonym for "moved ahead"

1 more reply

j / k navigate · click thread line to collapse