[GitHub] [kafka] feyman2016 commented on a change in pull request #9270: [WIP] KAFKA-10284: Group membership update due to static member rejoin should be persisted

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

feyman2016 commented on a change in pull request #9270:
URL: https://github.com/apache/kafka/pull/9270#discussion_r494424452



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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) {
+                warn(s"Failed to persist metadata for group ${group.groupId}: ${error.message}")
+              }
+            }
+          })
+          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))
+        } else {
+          maybePrepareRebalance(group, s"Group's selectedProtocol will change because static member ${member.memberId} with instance id $groupInstanceId joined with change of protocol")

Review comment:
       For example, if previously there are one leader + one follower(both static) in a group, the protocols are: `List(("range", metadata), ("roundrobin", metadata))` for both, and current selected protocol is `range`, if later the follower join again with protocols: `List(("roundrobin", metadata))`, and the selectedProtocol should be `roundrobin`, now, the selectedProtocol and the actual assignment is not consistent, here I let it rebalance to make sure that the selectedProtocol and actual assignment are consistent. On the other way around, if we don't do the rebalance, we cannot successfully persist the group since this line `val metadata = memberMetadata.metadata(protocol)` in `kafka.coordinator.group.GroupMetadataManager#groupMetadataValue` will fail.




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