Ordering guarantees

Global ordering does not scale; most systems guarantee order per key by sending all events of one key to the same partition. Choose the key so that events that must stay ordered share it.

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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