Hi Guozhang,
Isn't it also possible to lose messages even if the preferred leader is in
the ISR, when the current leader is ahead by a few messages, but the
preferred leader still has not caught up?
Thanks,
Jad.
On Thu, Jul 24, 2014 at 4:59 PM, Guozhang Wang <wangg...@gmail.com> wrote:
> 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
>
--
*Jad Naous* | Engineering | AppDynamics
<http://www.appdynamics.com>
