Guozhang Wang created KAFKA-8420:
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Summary: Graceful handling when consumer switches from subscribe
to manual assign
Key: KAFKA-8420
URL: https://issues.apache.org/jira/browse/KAFKA-8420
Project: Kafka
Issue Type: Improvement
Components: consumer
Reporter: Guozhang Wang
Today if a consumer switches between subscribe (and hence relies on group
rebalance to get assignment) and manual assign, it may cause unnecessary
rebalances. For example:
1. consumer.subscribe();
2. consumer.poll(); // join-group request sent, returns empty because poll
timeout
3. consumer.unsubscribe();
4. consumer.assign(..);
5. consumer.poll(); // sync-group request received, and the assigned
partitions does not match the current subscription-state. In this case it will
tries to re-join which is not necessary.
In the worst case (i.e. leader keep sending incompatible assignment), this
would case the consumer to fall into endless re-joins.
Although it is not a very common usage scenario, it still worth being better
handled than the status-quo.
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