Hi Jad,
Thanks for bring this up. It seems to be a valid issue: in the current auto
leader rebalancer thread's logic, if the imbalance ratio threshold is
violated, then it will trigger the preferred leader election whether or not
the preferred leader is in ISR or not.
Guozhang
On Thu, Jul 24, 2014 at 4:21 PM, Jad Naous <jad.na...@appdynamics.com>
wrote:
> Hi,
>
> I have a test that continuously sends messages to one broker, brings up
> another broker, and adds it as a replica for all partitions, with it being
> the preferred replica for some. I have auto.leader.rebalance.enable=true,
> so replica election gets triggered. Data is being pumped to the old broker
> all the while. It seems that some data gets lost while switching over to
> the new leader. Is this a bug, or do I have something misconfigured? I also
> have request.required.acks=-1 on the producer.
>
> Here's what I think is happening:
>
> 1. Producer writes message to broker 0, [EventServiceUpsertTopic,13], w/
> broker 0 currently leader, with ISR=(0), so write returns successfully,
> even when acks = -1. Correlation id 35836
>
> Producer log:
>
> [2014-07-24 14:44:26,991] [DEBUG] [dw-97 - PATCH
>
> /v1/events/type_for_test_bringupNewBroker_shouldRebalance_shouldNotLoseData/event?_idPath=idField&_mergeFields=field1]
> [kafka.producer.BrokerPartitionInfo] Partition
> [EventServiceUpsertTopic,13] has leader 0
>
> [2014-07-24 14:44:26,993] [DEBUG] [dw-97 - PATCH
>
> /v1/events/type_for_test_bringupNewBroker_shouldRebalance_shouldNotLoseData/event?_idPath=idField&_mergeFields=field1]
> [k.producer.async.DefaultEventHandler] Producer sent messages with
> correlation id 35836 for topics [EventServiceUpsertTopic,13] to broker 0 on
> localhost:56821
> 2. Broker 1 is still catching up
>
> Broker 0 Log:
>
> [2014-07-24 14:44:26,992] [DEBUG] [kafka-request-handler-3]
> [kafka.cluster.Partition] Partition [EventServiceUpsertTopic,13] on broker
> 0: Old hw for partition [EventServiceUpsertTopic,13] is 971. New hw is 971.
> All leo's are 975,971
>
> [2014-07-24 14:44:26,992] [DEBUG] [kafka-request-handler-3]
> [kafka.server.KafkaApis] [KafkaApi-0] Produce to local log in 0 ms
>
> [2014-07-24 14:44:26,992] [DEBUG] [kafka-processor-56821-0]
> [kafka.request.logger] Completed request:Name: ProducerRequest; Version:
> 0; CorrelationId: 35836; ClientId: ; RequiredAcks: -1; AckTimeoutMs: 10000
> ms from client /127.0.0.1:57086
>
> ;totalTime:0,requestQueueTime:0,localTime:0,remoteTime:0,responseQueueTime:0,sendTime:0
> 3. Leader election is triggered by the scheduler:
>
> Broker 0 Log:
>
> [2014-07-24 14:44:26,991] [INFO ] [kafka-scheduler-0]
> [k.c.PreferredReplicaPartitionLeaderSelector]
> [PreferredReplicaPartitionLeaderSelector]: Current leader 0 for partition [
> EventServiceUpsertTopic,13] is not the preferred replica. Trigerring
> preferred replica leader election
>
> [2014-07-24 14:44:26,993] [DEBUG] [kafka-scheduler-0]
> [kafka.utils.ZkUtils$] Conditional update of path
> /brokers/topics/EventServiceUpsertTopic/partitions/13/state with value
> {"controller_epoch":1,"leader":1,"version":1,"leader_epoch":3,"isr":[0,1]}
> and expected version 3 succeeded, returning the new version: 4
>
> [2014-07-24 14:44:26,994] [DEBUG] [kafka-scheduler-0]
> [k.controller.PartitionStateMachine] [Partition state machine on
> Controller 0]: After leader election, leader cache is updated to
> Map(<Snipped>(Leader:1,ISR:0,1,LeaderEpoch:3,ControllerEpoch:1),<EndSnip>)
>
> [2014-07-24 14:44:26,994] [INFO ] [kafka-scheduler-0]
> [kafka.controller.KafkaController] [Controller 0]: Partition [
> EventServiceUpsertTopic,13] completed preferred replica leader election.
> New leader is 1
> 4. Broker 1 is still behind, but it sets the high water mark to 971!!!
>
> Broker 1 Log:
>
> [2014-07-24 14:44:26,999] [INFO ] [kafka-request-handler-6]
> [kafka.server.ReplicaFetcherManager] [ReplicaFetcherManager on broker 1]
> Removed fetcher for partitions [EventServiceUpsertTopic,13]
>
> [2014-07-24 14:44:27,000] [DEBUG] [kafka-request-handler-6]
> [kafka.cluster.Partition] Partition [EventServiceUpsertTopic,13] on broker
> 1: Old hw for partition [EventServiceUpsertTopic,13] is 970. New hw is -1.
> All leo's are -1,971
>
> [2014-07-24 14:44:27,098] [DEBUG] [kafka-request-handler-3]
> [kafka.server.KafkaApis] [KafkaApi-1] Maybe update partition HW due to
> fetch request: Name: FetchRequest; Version: 0; CorrelationId: 1; ClientId:
> ReplicaFetcherThread-0-1; ReplicaId: 0; MaxWait: 500 ms; MinBytes: 1 bytes;
> RequestInfo: [EventServiceUpsertTopic,13] ->
> PartitionFetchInfo(971,1048576), <Snipped>
>
> [2014-07-24 14:44:27,098] [DEBUG] [kafka-request-handler-3]
> [kafka.cluster.Partition] Partition [EventServiceUpsertTopic,13] on broker
> 1: Recording follower 0 position 971 for partition [
> EventServiceUpsertTopic,13].
>
> [2014-07-24 14:44:27,100] [DEBUG] [kafka-request-handler-3]
> [kafka.cluster.Partition] Partition [EventServiceUpsertTopic,13] on broker
> 1: Highwatermark for partition [EventServiceUpsertTopic,13] updated to 971
> 5. Consumer is none the wiser. All data that was in offsets 972-975 doesn't
> show up!
>
> I tried this with 2 initial replicas, and adding a 3rd which is supposed to
> be the leader for some new partitions, and this problem also happens there.
> The log on the old leader gets truncated to the offset on the new leader.
> What's the solution? Can I make a new broker leader for partitions that are
> currently active without losing data?
>
> Thanks,
> Jad.
>
> --
> *Jad Naous* | Engineering | AppDynamics
> <http://www.appdynamics.com>
>
--
-- Guozhang
