Consumer groups

Consumers in a group share the partitions of a topic, each partition read by one consumer. Adding consumers beyond the number of partitions leaves them idle.

Where it shows up in real systems

  • Event log

    Events are kept for the retention period, so new consumers can replay history. Order is guaranteed only within a partition, and a consumer group can use at most one consumer per partition: partitions cap your parallelism.

    In production: Apache Kafka (Confluent, Amazon MSK), Amazon Kinesis, Redpanda, Azure Event Hubs, Apache Pulsar

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