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https://issues.apache.org/jira/browse/KAFKA-16944?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17856061#comment-17856061
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Ritika Reddy commented on KAFKA-16944:
--------------------------------------
Hey! Thanks for showing interest in this task! We've already started working on
this internally so I think we're good for now!
> Range assignor doesn't co-partition with stickiness
> ---------------------------------------------------
>
> Key: KAFKA-16944
> URL: https://issues.apache.org/jira/browse/KAFKA-16944
> Project: Kafka
> Issue Type: Sub-task
> Reporter: Ritika Reddy
> Assignee: Ritika Reddy
> Priority: Major
>
> When stickiness is considered during range assignments, it is possible that
> in certain cases where co-partitioning is guaranteed we fail.
> An example would be:
> Consider two topics T1, T2 with 3 partitions each and three members A, B, C.
> Let's say the existing assignment (for whatever reason) is:
> {quote}A -> T1P0 || B -> T1P1, T2P0, T2P1, T2P2 || C -> T1P2
> {quote}
> Now we trigger a rebalance with the following subscriptions where all members
> are subscribed to both topics everything else is the same
> {quote}A -> T1, T2 || B -> T1, T2 || C -> T1, T2
> {quote}
> Since all the topics have an equal number of partitions and all the members
> are subscribed to the same set of topics we would expect co-partitioning
> right so would we want the final assignment returned to be
> {quote}A -> T1P0, T2P0 || B -> T1P1, T2P1 || C -> T1P2, T2P2
> {quote}
> SO currently the client side assignor returns the following but it's because
> they don't assign sticky partitions
> {{{}C=[topic1-2, topic2-2], B=[topic1-1, topic2-1], A=[topic1-0,
> topic2-0]{}}}Our
>
> Server side assignor returns:
> (The partitions in bold are the sticky partitions)
> {{{}A=MemberAssignment(targetPartitions={topic2=[1],
> }}\{{{}{*}topic1=[0]{*}{}}}{{{}}),
> B=MemberAssignment(targetPartitions={{}}}{{{}*topic2=[0]*{}}}{{{},
> {{}}}}{{{}*topic1=[1]*{}}}{{{}}),
> C=MemberAssignment(targetPartitions={topic2=[2], {{}}}}{{{}*topic1=[2]*{}}}
> *As seen above co-partitioning is expected but not returned.*
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