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https://issues.apache.org/jira/browse/KAFKA-3438?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15498293#comment-15498293
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Ben Stopford commented on KAFKA-3438:
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Sorry, missed your original comment. Go for it.
> Rack Aware Replica Reassignment should warn of overloaded brokers
> -----------------------------------------------------------------
>
> Key: KAFKA-3438
> URL: https://issues.apache.org/jira/browse/KAFKA-3438
> Project: Kafka
> Issue Type: Improvement
> Affects Versions: 0.10.0.0
> Reporter: Ben Stopford
> Assignee: Vahid Hashemian
> Fix For: 0.10.1.0
>
>
> We've changed the replica reassignment code to be rack aware.
> One problem that might catch users out would be that they rebalance the
> cluster using kafka-reassign-partitions.sh but their rack configuration means
> that some high proportion of replicas are pushed onto a single, or small
> number of, brokers.
> This should be an easy problem to avoid, by changing the rack assignment
> information, but we should probably warn users if they are going to create
> something that is unbalanced.
> So imagine I have a Kafka cluster of 12 nodes spread over two racks with rack
> awareness enabled. If I add a 13th machine, on a new rack, and run the
> rebalance tool, that new machine will get ~6x as many replicas as the least
> loaded broker.
> Suggest a warning be added to the tool output when --generate is called.
> "The most loaded broker has 2.3x as many replicas as the the least loaded
> broker. This is likely due to an uneven distribution of brokers across racks.
> You're advised to alter the rack config so there are approximately the same
> number of brokers per rack" and displays the individual rack→#brokers and
> broker→#replicas data for the proposed move.
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