hardScenarioDesignSeniorStaff
How do you achieve true exactly-once semantics in Flink across source, state, and sink without cratering throughput?
2 min readUpdated 2026-08-15
Answer
Short answer
An analysis of the architectural reality of exactly-once guarantees in Flink, from distributed snapshots to two-phase commits.
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Likely follow-ups
- How do you handle a sink that has no transactional semantics at all, such as a plain REST API?
- What happens to your exactly-once guarantees when you need to rescale a stateful operator's parallelism?
- How would you detect in production that your two-phase commit sink is silently duplicating records?
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