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https://issues.apache.org/jira/browse/KAFKA-17747?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Jacot resolved KAFKA-17747.
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Resolution: Fixed
> Trigger rebalance on rack topology changes
> ------------------------------------------
>
> Key: KAFKA-17747
> URL: https://issues.apache.org/jira/browse/KAFKA-17747
> Project: Kafka
> Issue Type: Improvement
> Components: group-coordinator
> Reporter: David Jacot
> Assignee: PoAn Yang
> Priority: Major
> Fix For: 4.1.0
>
>
> At the moment, we trigger a rebalance of the consumer group only when the
> number of partitions of a topic has changed (e.g. increased the number of
> partitions). We tried to extend this mechanism to also take racks into
> consideration (see [this|https://github.com/apache/kafka/pull/17233]) but it
> turned out to be to expensive from a memory and cpu perspective. It was also
> bad because we ended up duplicating many of the information already present
> in the Metadata image. We should design a better way to do this and it may
> require a KIP depending on the solution.
> I have two high level ideas in mind:
> # One way would be to include a new epoch to the topic metadata stored in
> the controlled. This new epoch could be incremented whenever the topology of
> the topic has changed (e.g. adding partition, reassignment, etc.). Then we
> could store the epoch in the group coordinator to detect changes and
> rebalance the group. The downside of this approach is that it couple the
> group coordinator to the controller.
> # Another way would be to come up with a way to compute a hash of the
> current topology on the topic(s). The digest would then be stored in the
> group coordinator and used to detect changes. The downside of this is that it
> requires to re-compute the hash to determine whether this is a change or not.
> Option 1) would be a bit more efficient because the controller knows when the
> epoch must be bumped.
> We should explore those ideas and possibly other ones.
>
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