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https://issues.apache.org/jira/browse/KAFKA-6481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16338465#comment-16338465
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ASF GitHub Bot commented on KAFKA-6481:
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gitlw opened a new pull request #4472: KAFKA-6481: Improving performance of the
function ControllerChannelManager.addUpd…
URL: https://github.com/apache/kafka/pull/4472
…ateMetadataRequestForBrokers
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> Improving performance of the function
> ControllerChannelManager.addUpdateMetadataRequestForBrokers
> -------------------------------------------------------------------------------------------------
>
> Key: KAFKA-6481
> URL: https://issues.apache.org/jira/browse/KAFKA-6481
> Project: Kafka
> Issue Type: Improvement
> Reporter: Lucas Wang
> Priority: Minor
>
> The function ControllerChannelManager.addUpdateMetadataRequestForBrokers
> should only process the partitions specified in the partitions parameter,
> i.e. the 2nd parameter, and avoid iterating through the set of partitions in
> TopicDeletionManager.partitionsToBeDeleted.
>
> Here is why the current code can be a problem:
> The number of partitions-to-be-deleted stored in the field
> TopicDeletionManager.partitionsToBeDeleted can become quite large under
> certain scenarios. For instance, if a topic a0 has dead replicas, the topic
> a0 would be marked as ineligible for deletion, and its partitions will be
> retained in the field TopicDeletionManager.partitionsToBeDeleted for future
> retries.
> With a large set of partitions in TopicDeletionManager.partitionsToBeDeleted,
> if some replicas in another topic a1 needs to be transitioned to
> OfflineReplica state, possibly because of a broker going offline, a call
> stack listed as following will happen on the controller, causing a iteration
> of the whole partitions-to-be-deleted set for every single affected partition.
> controller.topicDeletionManager.partitionsToBeDeleted.foreach(partition
> => updateMetadataRequestPartitionInfo(partition, beingDeleted = true))
> ControllerBrokerRequestBatch.addUpdateMetadataRequestForBrokers
> ControllerBrokerRequestBatch.addLeaderAndIsrRequestForBrokers
> inside a for-loop for each partition
> ReplicaStateMachine.doHandleStateChanges
> ReplicaStateMachine.handleStateChanges
> KafkaController.onReplicasBecomeOffline
> KafkaController.onBrokerFailure
> How to reproduce the problem:
> 1. Cretae a cluster with 2 brokers having id 1 and 2
> 2. Create a topic having 10 partitions and deliberately assign the replicas
> to non-existing brokers, i.e.
> ./bin/kafka-topics.sh --zookeeper localhost:2181 --create --topic a0
> --replica-assignment `echo -n 3:4; for i in \`seq 9\`; do echo -n ,3:4; done`
> 3. Delete the topic and cause all of its partitions to be retained in the
> field TopicDeletionManager.partitionsToBeDeleted, since the topic has dead
> replicas, and is ineligible for deletion.
> 4. Create another topic a1 also having 10 partitions, i.e.
> ./bin/kafka-topics.sh --zookeeper localhost:2181 --create --topic a1
> --replica-assignment `echo -n 1:2; for i in \`seq 9\`; do echo -n ,1:2; done`
> 5. Kill the broker 2 and cause the replicas on broker 2 to be transitioned to
> OfflineReplica state on the controller.
> 6. Verify that the following log message appear over 200 times in the
> controller.log file, one for each iteration of the a0 partitions
> "Leader not yet assigned for partition [a0,..]. Skip sending
> UpdateMetadataRequest."
>
> What happened was
> 1. During controlled shutdown, the function
> KafkaController.doControlledShutdown calls
> replicaStateMachine.handleStateChanges to transition all the replicas on
> broker 2 to OfflineState. That in turn generates 100 (10 x 10) entries of the
> logs above.
> 2. When the broker zNode is gone in ZK, the function
> KafkaController.onBrokerFailure calls KafkaController.onReplicasBecomeOffline
> to transition all the replicas on broker 2 to OfflineState. And this again
> generates 100 (10 x 10) entries of the logs above.
> After applying the patch in this RB, I've verified that by going through the
> steps above, broker 2 going offline NO LONGER generates log entries for the
> a0 partitions.
> Also I've verified that topic deletion for topic a1 still works fine.
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