[jira] [Commented] (KAFKA-762) Improve second replica assignment

["Guozhang Wang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-762?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13582461#comment-13582461 ] 

Guozhang Wang commented on KAFKA-762:
-------------------------------------

Reviewed the patch, looks good to me. 

Just one question about the motivation: in normal settings where # brokers is larger than # replicas, even if the first replica of a partition is assigned to the same broker, their following replicas may not be assigned to the same broker as long as their partition id are not the same. Just from the example from the code: P1 of Topic1 and P5 of Topic2 could have their first replicas assigned to the same broker, while their following replicas are not assigned to the same brokers.
                
> Improve second replica assignment
> ---------------------------------
>
>                 Key: KAFKA-762
>                 URL: https://issues.apache.org/jira/browse/KAFKA-762
>             Project: Kafka
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 0.8
>            Reporter: Jun Rao
>            Assignee: Jun Rao
>            Priority: Blocker
>         Attachments: kafka-762_v1.patch
>
>
> Currently, for partitions from different topics, if the first replica is assigned to the same broker, their second replica is also assigned to the same broker. This means that when a broker fails, many leaders on the failed broker will be moved to the same broker, and thus introduces more load on that broker.

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