Lucas Wang created KAFKA-6481:
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Summary: 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
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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