u/Altruistic_Shift_335

always assumed if send() didn't throw an error the message was in the broker, done. then someone mentioned it's basically fire-and-forget unless you're handling the callback or have acks=all set, and now i don't really know what "delivered" means here anymore. do you always attach a callback? check offsets after? has this ever quietly bitten you, like a message just vanished and you only found out way later

Curious what people have actually hit in production - messages landing in an unexpected partition, ordering breaking because of a key choice made early and never revisited, a 'random' bug that turned out to be perfectly deterministic once you understood the hashing. What was the actual symptom before you knew the cause, and what was the fix — repartition, change the key, something else?