[jolynch]

This is exactly the kind of stuff I wrote this post about. The first (exactly once) is actually just at-least-once with deduplication based on a counter. To reliably process the events, however, you need to make your downstream idempotent as well. Think of it like your event processor might fail, so even if you only receive the message "once" if you can fail processing it you still have to think about retries. In my opinion it would be explicitly better for the event system to provide "at least once" and intentionally duplicate events on occasion to test your processors ability to handle duplicates.

The second (lock) is actually a lease fwict, and writing code in the locked body that assumes it will be truly mutually exclusive is pretty dangerous (see the linked post from Martin [1] for why).

[1] https://martin.kleppmann.com/2016/02/08/how-to-do-distribute...

[lopatin]

> In my opinion it would be explicitly better for the event system to provide "at least once" and intentionally duplicate events on occasion to test your processors ability to handle duplicates.

You're a madman, but I think you're right.

Thanks for the locking link.