Sean Quah created KAFKA-18688:
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             Summary: Uniform homogeneous assignment is not always stable
                 Key: KAFKA-18688
                 URL: https://issues.apache.org/jira/browse/KAFKA-18688
             Project: Kafka
          Issue Type: Bug
          Components: group-coordinator
            Reporter: Sean Quah


The uniform homogeneous assignor assigns partitions to group members which have 
identical subscriptions. When the number of partitions is not divisible by the 
number of members, some members will end up with 1 more partition than others.

The assignor iterates over members and chooses the first {{partitions % 
members}} members to have the extra partition. Even when the existing 
assignment is balanced, the assignor can decide that a different set of members 
should have the extra partition, due to the iteration order.

This means that when a static member is replaced and the assignment is 
recomputed, it may gain or lose a single partition.



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