Konstantine Karantasis created KAFKA-8332:
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Summary: 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
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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