Jason Gustafson created KAFKA-9081:
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             Summary: Loosen reassignment completion to handle existing URPs
                 Key: KAFKA-9081
                 URL: https://issues.apache.org/jira/browse/KAFKA-9081
             Project: Kafka
          Issue Type: Improvement
            Reporter: Jason Gustafson
            Assignee: Jason Gustafson


Currently a reassignment completes only when all target replicas have joined 
the ISR. If a partition is already under-replicated when a reassignment begins, 
then reassignment completion depends also on resolving the prior condition. 

For example, suppose we have an assignment of (1, 2, 3) and the ISR is (1, 2). 
If we reassign to (1, 3, 4), then reassignment will be blocked until 3 rejoins 
the ISR. In particular, this means you cannot reassign a partition with an 
offline replica unless the reassignment removes that replica.

I think we can loosen completion criteria for these cases. The purpose of the 
reassignment state machine is really to bring the new replicas in sync and not 
to resolve a pre-existing condition. Especially in cases where the URP is a 
result of increased load from the reassignment, we want the completion to not 
be delayed.

 

 



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