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https://issues.apache.org/jira/browse/KAFKA-6681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16413789#comment-16413789
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Narayan Periwal commented on KAFKA-6681:
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[~yuzhih...@gmail.com],
We faced yet another such issue, on server side we found these logs in this case
{noformat}
[2018-03-23 18:59:16,560] INFO [GroupCoordinator 6]: Stabilized group
prod-m10n-event-batcher-billablebeaconams1 generation 6
(kafka.coordinator.GroupCoordinator)
[2018-03-23 18:59:46,561] INFO [GroupCoordinator 6]: Preparing to restabilize
group prod-m10n-event-batcher-billablebeaconams1 with old generation 6
(kafka.coordinator.GroupCoordinator)
[2018-03-23 18:59:46,833] INFO [GroupCoordinator 6]: Stabilized group
prod-m10n-event-batcher-billablebeaconams1 generation 7
(kafka.coordinator.GroupCoordinator)
{noformat}
> Two instances of kafka consumer reading the same partition within a consumer
> group
> ----------------------------------------------------------------------------------
>
> Key: KAFKA-6681
> URL: https://issues.apache.org/jira/browse/KAFKA-6681
> Project: Kafka
> Issue Type: Bug
> Components: consumer
> Affects Versions: 0.10.2.1
> Reporter: Narayan Periwal
> Priority: Critical
> Attachments: server-1.log, server-2.log
>
>
> We have seen this issue with the Kafka consumer, the new library that got
> introduced in 0.9
> With this new client, the group management is done by kafka coordinator,
> which is one of the kafka broker.
> We are using Kafka broker 0.10.2.1 and consumer client version is also
> 0.10.2.1
> The issue that we have faced is that, after rebalancing, some of the
> partitions gets consumed by 2 instances within a consumer group, leading to
> duplication of the entire partition data. Both the instances continue to read
> until the next rebalancing, or the restart of those clients.
> It looks like that a particular consumer goes on fetching the data from a
> partition, but the broker is not able to identify this "stale" consumer
> instance.
> During this time, we also see the underreplicated partition metrics spiking.
> We have hit this twice in production. Please look at it the earliest.
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