[throwup238]

> their MVP was not auditable and thus not compliant with financial regulations and also not scalable (high usage and fault tolerance).

There it is. My automatic response to any questions about event sourcing is “if you have to ask, you don’t need it.” This is one of those situations where the explosion in complexity somewhat makes sense: when you need legally enforced auditability.

Event sourcing is a really cool architecture that makes theoretical sense but the yak shaving needed to implement it is at least an order of magnitude more than any other design.

[chuckadams]

I'd call it a trade-off. I've done event sourcing for systems that didn't really need it, and the ability to fix things retroactively by just replaying the log through the corrected pipeline of processors was marvelous. It lends itself to functional programming with effects instead of banging on global state wherever and whenever, and that pays dividends. But there's no free lunch, and pipelines could get complex by needing to track "epochs" and keeping bug-compatible behavior for old messages that would be patched downstream. Since the system just built persisted state at the end, I could checkpoint it at a new state and retire the older epochs. Doubtful that would that pass a rigorous audit, but if that's not one of your requirements, you really can do event sourcing halfway and still reap a lot of the benefits.

[marcosdumay]

Yes. And that's usually anything that touches money or is limited by it.

But you don't need to decide to use it. The people describing the requirements will tell you, insist on it, and threaten you if you don't do it.

[dmoy]

Yea I think that's a fair take.

If you peer underneath the covers of a lot of financial stuff, and it's effectively double entry accounting. Which is a giant ledger (or ledgers) of events

[kabes]

This! I've recently was hired to fix a company that tried to build their own niche ERP over the last 10 years and they had totally drowned in the confluent kool-aid. There is very very few projects where event sourcing is the best solution.