Stock that drifts negative
An inventory topic is spread round-robin across twelve partitions for throughput. Decrement and increment events for the same item land on different partitions and get consumed in parallel, so they apply out of order.
Order is guaranteed inside a partition, not across them. Round-robin threw the guarantee away for throughput nobody measured.
Boundaries, outermost first: Topic: Partition 3 (FAILED: out of order), Partition 1 (FAILED: out of order), Partition 2 Outside every boundary: Producer, an empty slot for the how events are routed Connections: Producer publishes to how events are routed (step 1) how events are routed publishes to Partition 1 — same item, same partition (step 2) how events are routed publishes to Partition 2 how events are routed publishes to Partition 3