[codebeaker]

I'm well aware that there's no absolute standards for this, but I've built a number of CQRS systems, and I didn't ever have idempotency IDs as a core tenant of the system.

What literature, or framework or ecosystem holds this to be a hard-and-fast requirement of CQRS?

Personally I've solved this problem similar to Git, modelling CQRS on top of Merkle trees so your system at least knows if your incoming edit (command|commit) is being applied on HEAD (no changes to the model since the command started) or to HEAD+n (needing to re-run some command validations, and "rebase" the incoming command).

[lolski]

I don't think there is any "standard" that strictly governs the implementation of a CQRS system. We just need to be aware of the nuances of the fault-tolerance aspect in distributed systems:

- idempotency is ONLY a hard-requirement if the events are transmitted via lossy channels such as network. ID is one out of several ways to ensure idempotency. If you're implementing CQRS for your distributed system then it's needed - otherwise, if the events aren't lossy and can be processed atomically, you don't need to ensure idempotency. think implementing CQRS for your user interface where events are just transmitted between different objects in memory rather than via network

[regularfry]

That's generating an idempotency ID on the fly, isn't it?