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https://issues.apache.org/jira/browse/KAFKA-20778?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lianet Magrans resolved KAFKA-20778.
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Resolution: Fixed
> Improve classic consumer rack-aware double rebalance on replica bounce
> ----------------------------------------------------------------------
>
> Key: KAFKA-20778
> URL: https://issues.apache.org/jira/browse/KAFKA-20778
> Project: Kafka
> Issue Type: Improvement
> Components: clients, consumer
> Reporter: Lianet Magrans
> Assignee: Lianet Magrans
> Priority: Major
> Fix For: 4.4.0
>
>
> When a replica is bounced , the classic consumer goes through a double
> rebalance because when it notices a rack ID changed from rackX to null, then
> from null to rackX, unneeded rebalance noise.
> Consider if we could avoid this double rebalance by identifying that the case
> is that the replica is down (based on the existing flow that knows that the
> replica lost its "host", not only the rack).
> This issue only affects the classic consumer, where rebalances are triggered
> client-side based on the metadata (a replica temporarily shows as "emtpy
> node", no host or rack), but the client blindly takes that as rack=null and
> compares that null to the previous rack ID. With the new consumer group
> protocol there is no rebalance triggered by the GC in this case of temporary
> replica bounce, as the rack info remains unchanged (replica metadata
> available, unchanged, while temporarily down)
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