[jira] [Commented] (KAFKA-8359) Reconsider default for leader imbalance percentage

["Romain Hardouin (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-8359?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17164538#comment-17164538 ] 

Romain Hardouin commented on KAFKA-8359:
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{quote}[...] there is no major downside to set leader imbalance percentage to 0.
{quote}
Does it mean there are _minor_ downsides?

Following the principle of least astonishment, the default value should be 0 because users expect to have balanced clusters when using {{auto.leader.rebalance.enable=true}} 

 

> Reconsider default for leader imbalance percentage
> --------------------------------------------------
>
>                 Key: KAFKA-8359
>                 URL: https://issues.apache.org/jira/browse/KAFKA-8359
>             Project: Kafka
>          Issue Type: Improvement
>            Reporter: Dhruvil Shah
>            Priority: Major
>
> By default, the leader imbalance ratio is 10%. This means that the controller won't trigger preferred leader election for a broker unless the ratio of the number of partitions a broker is the current leader of and the number of partitions it is the preferred leader of is off by more than 10%. The problem is when a broker is catching up after a restart, the smallest topics tend to catch up first and the largest ones later, so the 10% remaining difference may not be proportional to the broker's load. To keep better balance in the cluster, we should consider setting `leader.imbalance.per.broker.percentage=0` by default so that the preferred leaders are always elected.



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