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From "Konstantine Karantasis (JIRA)" <j...@apache.org>
Subject [jira] [Created] (KAFKA-8332) Regression in handling of JoinGroupRequest disallows deterministic protocol selection based on order of preference
Date Tue, 07 May 2019 23:38:00 GMT
Konstantine Karantasis created KAFKA-8332:
---------------------------------------------

             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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