Partitioned Consumption

1. The Pattern

Split the stream into partitions by key. Every event for a given key lands in the same partition. Each partition is read by exactly one consumer at a time. Order holds strictly within a partition. The contract: order per key, parallelism across keys.

This lesson formalizes a deal the course has made informally for eight modules. The queue lesson's Q3 had a refund processed before its charge. Its cure was "partition by customer ID," with none of the fine print