Backend & systems·Queues, streams and delivery semantics
you add a second worker and the partitions get split between them so each message is still only processed once.
Consumer group
A set of consumers that jointly consume a stream, with each partition assigned to exactly one member. It is how a log-based system gives you both queue semantics and horizontal scaling. Parallelism is capped by partition count: adding consumers past that number gives you idle processes, not throughput.