[mbucc]

I have been using event-based persistence, and while performance is definitely a bonus, the win for me is the ability to replay the transaction log.

For example, let's say you log each page view and include the referer in that transaction. Initially, the only state you maintain (in memory) is the count of page views.

Three months after your system is on-line, you decide you want to take a closer look at who is sending you traffic. So, you update the business logic that processes the pageview_transaction to count page views by referer, perhaps a count of domains by day (for up to 365 days). Replay the log and you will now have that state for the entire history of your app.

I expect there will be benefits for debugging as well, since I can replay the transaction log with a local, annotated version of the app to figure out specific sequence of real-world transactions that surfaced the bug.

And you can use SQL if you like. You just have to keep your transaction processing fast (e.g., by using an in-memory db).

If you are interested, here's a Python implementation: https://github.com/PetrGlad/python-prevayler.