Streams, Keys, and Operators

Partitioning, keyBy, key groups, operator chains — the same request must always meet the same subtask

How records find their operator. keyBy is a routing decision that also decides where state can live. GatewayMeter assembles each request's lifecycle from its events; drop the keyBy and one request's start and completion land on different subtasks and no record is ever emitted.

Estimated time: 60 minutes

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