[jira] [Updated] (KAFKA-256) Bug in the consumer rebalancing logic leads to the consumer not pulling data from some partitions

["Neha Narkhede (Updated) (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-256?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Neha Narkhede updated KAFKA-256:
--------------------------------

    Comment: was deleted

(was: Might as well fix KAFKA-262 as part of this patch)
    
> Bug in the consumer rebalancing logic leads to the consumer not pulling data from some partitions
> -------------------------------------------------------------------------------------------------
>
>                 Key: KAFKA-256
>                 URL: https://issues.apache.org/jira/browse/KAFKA-256
>             Project: Kafka
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 0.7
>            Reporter: Neha Narkhede
>            Assignee: Neha Narkhede
>            Priority: Critical
>             Fix For: 0.7.1
>
>         Attachments: kafka-256-v2.patch, kafka-256-v3.patch
>
>
> There is a bug in the consumer rebalancing logic that makes a consumer not pull data from some partitions for a topic. It recovers only after the consumer group is restarted and doesn't hit this bug again.
> Here is the observed behavior of the consumer when it hits the bug -
> 1. Consumer is consuming 2 topics with 1 partition each on 2 brokers
> 2. Broker 2 is bounced
> 3. Rebalancing operation triggers for topic_2, where the consumer decides to now consume data only from Broker 1 for topic_2
> 4. During the rebalancing operation, ZK has not yet deleted the /brokers/topics/topic_1/broker_2, so the consumer still decides to consumer from both brokers for topic_1
> 5. While restarting the fetchers, it tries to restart fetcher for broker 2 and throws a RuntimeException. Before this, it has successfully started fetcher for broker 1 and is consuming data from broker_1
> 6. This exception trickles all the way upto syncedRebalance API and the oldPartitionsPerTopicMap does not get updated to reflect that for topic_2, the consumer has now seen only broker_1. It still points to topic_2 -> broker_1, broker_2
> 7. Next rebalancing attempt gets triggered
> 8. By now, broker 2 is restarted and registered in zookeeper
> 9. For topic_2, the consumer tries to see if rebalancing needs to be done. Since it doesn't see a change in the cached topic partition map, it decides there is no need to rebalance.
> 10. It continues fetching only from broker_1

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