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