THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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The ISR expansion is triggered by the Fetch requests. Using Fetch requests makes the expansion synchronized. Broker is online → Fetch and catch up → candidate for ISR → expand with AlterPartition. The flow is straightforward and easy to maintain.
Using broker metadata requires more careful thinking about potential issues. For example, if the last fetch request comes super late, the leader already knows the new broker epoch and sends the AlterPartition with the new one, then the rebooted broker can still be added to ISR.
- Also, as a precautions check, the leader will only attempt to include the broker in ISR if the broker epoch from the metadata cache matches the epoch from the Fetch request.
The new behaviors break down:
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