Affects Version/s: None
Fix Version/s: None
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:
2. consumer.poll(); // join-group request sent, returns empty because poll timeout
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.