What Kafka Guarantees About Order

Kafka · lesson 6 of 34 · 3 min read

Get precise about where ordering holds, where it does not, and how to design keys around it.

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Key points

  • Order is guaranteed within a partition and nowhere else. There is no such thing as global topic ordering.
  • So: same key gives same partition gives ordered. Records with different keys may be processed in any order.
  • Retries could reorder records, except the producer is idempotent by default since Kafka 3.0, which preserves order across in-flight batches.
  • Adding partitions rehashes keys. For a short window one key can exist in two partitions, so old and new events interleave.
  • Multithreading inside a consumer breaks order too, unless each thread owns whole partitions or you shard threads by key.
  • If total ordering is truly required, you need one partition, and therefore one consumer. That is a throughput decision.

Order exists per partition. Choose keys as if ordering depends on them, because it does.

Rebalancing Without the Pain acks, Retries and Durability

This is a reading copy. The full lesson — with the visual explainer, the interactive lab and a Run button for the code — lives in the Kafka course, and every lesson in it is listed on the Kafka contents page.