[jgeraert]

> One thing that absolutely needs library/drivers is persistence of the event store. I say this having built my own as well as contributing to open source ones in the past. It is still a hard and not well solved problem to do this well. Again it can be simple, but in the real world it isn't usually that simple.

Would it also be such a hard thing to do if you can delegate the actual persistence to something like a rdbms? What are the typical pitfalls?

[dm3]

Having built a few RDBMS-based event stores - it's pretty easy to do. There are two parts that I can think of that are not completely trivial - appending events to the stream while respecting "expected version" modifiers with optimal concurrency and allowing for fast and light subscriptions to new events (e.g. LISTEN/NOTIFY in Postgres, ringbuffer on the client).

The good thing is that you can adapt the event store to your performance requirements and do the simplest thing possible in a huge amount of cases.