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by the_duke 282 days ago
Nice, will have a look!

I've had similar thoughts, but my concern was: if you have idempotent actions, then why not just encode them as actions in a log. Which just brings you to event sourcing, a quite well-known pattern.

If you go that route, then what do you need CRDTs for?
3 comments
ForHackernews 282 days ago
Doesn't event-sourcing imply that there's a single source-of-truth data store you can source them from? I'm not sure event sourcing says anything about resolving conflicts or consistency.
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evelant 282 days ago
The pattern I came up with is similar to event sourcing but with some CRDT and offline-first concepts mixed in. By using logical clocks and a client side postgres (pglite) it doesn't have to keep the entire event history for all time and the server side doesn't have to process actions/events at all beyond storing them. The clients do the resolution of state, not the server. Clients can operate offline as long as they like and the system still arrives at a consistent state. AFAIK this is different than most event sourcing patterns.

At least in my thinking/prototyping on the problem so far I think this solution offers some unique properties. It lets clients operate offline as long as they like. It delegates the heavy lifting of resolving state from actions/events to clients, requiring minimal server logic. It prevents unbounded growth of action logs by doing a sort of "rebase" for clients beyond a cutoff. It seems to me like it maximally preserves intentions without requiring specific conflict resolution logic. IMO worth exploring further.

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n0w 282 days ago
A CRDT is any data structure that meets the definition (associative, commutative, idempotent, etc...)

Event Sourcing is not strictly designed to achieve eventual consistency in the face of concurrent writes though. But that doesn't mean it can't be!

I've also been considering an intent based CRDT system for a while now (looking forward to checking out GPs link) and agree that it looks/sounds very much like Event Sourcing. It's worth while being clear on the definition/difference between the two though!

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