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https://issues.apache.org/jira/browse/KAFKA-8332?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16837770#comment-16837770
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ASF GitHub Bot commented on KAFKA-8332:
---------------------------------------
hachikuji commented on pull request #6695: KAFKA-8332: Restore determinism in
protocol selection during JoinGroupRequest handling
URL: https://github.com/apache/kafka/pull/6695
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> 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: Bob Barrett
> 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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