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https://issues.apache.org/jira/browse/KAFKA-1561?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Guozhang Wang resolved KAFKA-1561.
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Resolution: Fixed
> Data Loss for Incremented Replica Factor and Leader Election
> ------------------------------------------------------------
>
> Key: KAFKA-1561
> URL: https://issues.apache.org/jira/browse/KAFKA-1561
> Project: Kafka
> Issue Type: Bug
> Reporter: Guozhang Wang
> Assignee: Guozhang Wang
> Fix For: 0.11.0.0
>
> Attachments: broker0.log, broker2.log, consumer.log, producer.log
>
>
> This is reported on the mailing list (thanks to Jad).
> {quote}
> 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.
> {quote}
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