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https://issues.apache.org/jira/browse/KAFKA-8332?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ismael Juma updated KAFKA-8332:
-------------------------------
    Fix Version/s: 2.3.0

> Regression in handling of JoinGroupRequest disallows deterministic protocol 
> selection based on order of preference
> ------------------------------------------------------------------------------------------------------------------
>
>                 Key: KAFKA-8332
>                 URL: https://issues.apache.org/jira/browse/KAFKA-8332
>             Project: Kafka
>          Issue Type: Bug
>          Components: core
>            Reporter: Konstantine Karantasis
>            Assignee: Konstantine Karantasis
>            Priority: Blocker
>             Fix For: 2.3.0
>
>
> When a group of Kafka clients includes more than one embedded protocol in its 
> {{JoinGroupRequest}} along with its metadata, the group membership protocol 
> defines that the protocol which is supported by all the members of a group is 
> selected, and if more than one protocols are supported by all the members the 
> protocol is selected based on the order of preference as defined in the 
> {{JoinGroupRequest}}. 
> A recent change from type {{List}} to type {{Set}} for storing the set of 
> supported embedded protocols in the {{JoinGroupRequest}} combined with the 
> old type of handling with implicit types in the scala code, has introduced 
> non-determinism in the selection of the embedded protocol by the 
> {{GroupCoordinator}}, even though the underlying type of the Set in use is a 
> variant of LinkedHashSet (it respects order). 
> The relevant code is: 
> {code:java}
> // KafkaApis.scala
> val protocols = joinGroupRequest.data().protocols().asScala.map(protocol =>
>       (protocol.name, protocol.metadata)).toList
> {code}
>  



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