Ziyun Fu created KAFKA-21166:
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             Summary: sticky assignor maybe never converge
                 Key: KAFKA-21166
                 URL: https://issues.apache.org/jira/browse/KAFKA-21166
             Project: Kafka
          Issue Type: Improvement
            Reporter: Ziyun Fu


While running the fuzz test with other base seeds to task sticky assignor, I 
found some cases where standbys never be stable.

If we take the output of {{{}assign(){}}}, feed it back as the members' current 
assignment and call {{assign() }}again, some scenarios never reach a fixed 
point, cause a few standby tasks land on member1, move to member2 in the next 
round, come back to member1 in the round after that, and so on indefinitely.

Active tasks are not affected, only standbys. 

If this keep happening, every time there's a rebalance, member1 and member2 
will need to swap the standby and it's a extra cost for rebalance.



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