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https://issues.apache.org/jira/browse/KAFKA-8332?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16835212#comment-16835212
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Konstantine Karantasis commented on KAFKA-8332:
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[~bchen225242], minor is definitely an understatement for this bug. Jira will
help us track progress indeed. At the same time, by quickly looking at
[https://github.com/apache/kafka/pull/6626] I can say that maybe both fixes
makes sense. But I'll leave that up to reviewers. cc [~bob-barrett]
[~hachikuji] [~jagsancio]
> 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
>
> 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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