[GitHub] [kafka] vvcephei commented on a change in pull request #9270: KAFKA-10284: Group membership update due to static member rejoin should be persisted

[GitBox <gi...@apache.org>]

vvcephei commented on a change in pull request #9270:
URL: https://github.com/apache/kafka/pull/9270#discussion_r497818766



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File path: core/src/main/scala/kafka/coordinator/group/GroupCoordinator.scala
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@@ -1040,21 +1040,36 @@ class GroupCoordinator(val brokerId: Int,
 
     group.currentState match {
       case Stable =>
-        info(s"Static member joins during Stable stage will not trigger rebalance.")
-        group.maybeInvokeJoinCallback(member, JoinGroupResult(
-          members = List.empty,
-          memberId = newMemberId,
-          generationId = group.generationId,
-          protocolType = group.protocolType,
-          protocolName = group.protocolName,
-          // We want to avoid current leader performing trivial assignment while the group
-          // is in stable stage, because the new assignment in leader's next sync call
-          // won't be broadcast by a stable group. This could be guaranteed by
-          // always returning the old leader id so that the current leader won't assume itself
-          // as a leader based on the returned message, since the new member.id won't match
-          // returned leader id, therefore no assignment will be performed.
-          leaderId = currentLeader,
-          error = Errors.NONE))
+        // check if group's selectedProtocol of next generation will change, if not, simply store group to persist the
+        // updated static member, if yes, rebalance should be triggered to let the group's assignment and selectProtocol consistent
+        val selectedProtocolOfNextGeneration = group.selectProtocol
+        if (group.protocolName.contains(selectedProtocolOfNextGeneration)) {
+          info(s"Static member which joins during Stable stage and doesn't affect selectProtocol will not trigger rebalance.")
+          val groupAssignment: Map[String, Array[Byte]] = group.allMemberMetadata.map(member => member.memberId -> member.assignment).toMap
+          groupManager.storeGroup(group, groupAssignment, error => {
+            group.inLock {
+              if (error != Errors.NONE) {

Review comment:
       Hi @feyman2016 , I just noticed this PR. Thanks for picking this up!
   
   I'm wondering something along similar lines; should we move the whole join callback inside this block? It seems like that's the way we can delay the join group response until after the update is actually persisted.




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