[jira] [Commented] (KAFKA-8799) Support ability to pass global user data to consumers during Assignment

["Vinoth Chandar (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-8799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16906627#comment-16906627 ] 

Vinoth Chandar commented on KAFKA-8799:
---------------------------------------

[~guozhang] filed this for the longer term fix. 

> Support ability to pass global user data to consumers during Assignment
> -----------------------------------------------------------------------
>
>                 Key: KAFKA-8799
>                 URL: https://issues.apache.org/jira/browse/KAFKA-8799
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: Vinoth Chandar
>            Priority: Major
>
> This is a follow up from KAFKA-7149 
> *Background :* 
> Although we reduced the size of the AssignmentInfo object sent during each rebalance from leader to all followers in KAFKA-7149, we still repeat the same _partitionsByHost_ map for each host (all this when interactive queries are enabled) and thus still end up sending redundant bytes to the broker and also logging a large kafka message.
> With 100s of streams instances, this overhead can grow into tens of megabytes easily.  
> *Proposal :*
> Extend the group assignment protocol to be able to support passing of an additional byte[], which can now contain the HostInfo -> partitions/partitionsByHost data just one time. 
> {code}
> final class GroupAssignment {
>         private final Map<String, Assignment> assignments;
>         // bytes sent to each consumer from leader
>         private final byte[] globalUserData
>         ...
>     }
> {code}
>  
> This can generally be handy to any other application like Streams, that does some stateful processing or lightweight cluster management 
>  



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