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

["Sönke Liebau (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-8359?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16840262#comment-16840262 ] 

Sönke Liebau commented on KAFKA-8359:
-------------------------------------

I dug around a little as to where this default comes from, but the only thing that I could find is [this brief conversation|https://reviews.apache.org/r/15711/#comment56318].

Personally I think between the ability to customize this parameter, monitoring PreferredReplicaImbalanceCount and manually triggering a leader rebalance there is no real need to change the default behavior, but I am very happy to be convinced otherwise.

 

Would it as an alternative be useful to make this parameter dynamically updateable without cluster restart?

> 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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