System InternalsLearn ↗Message Queue (Kafka-style)PRODUCEPOLLJOINLEAVE

Message Queue (Kafka-style) — pick a scenario

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Partitions reassigning when the second consumer joins, and lag (log-end minus committed offset) shrinking as each group catches up.

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You'll learn

How a partitioned log scales consumers while preserving per-key order, and how committed offsets let groups read independently.

How it runs

Each PRODUCE hashes its key to a partition. Consumers JOIN a group and get partitions assigned round-robin; adding a consumer rebalances the assignment. Each group's committed offsets advance on POLL, independently of other groups.