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https://issues.apache.org/jira/browse/FLINK-10455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16835749#comment-16835749
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Chris Slotterback commented on FLINK-10455:
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The way I was able to reproduce this was forcing the job into a failed state by 
timing out writing a checkpoint on the filesystem. We occasionally see latency 
spikes in our env resulting in these job restarts. Most of the jobs are able to 
recover fine, but when using exactly once for the kafka producer the job gets 
stuck in this loop. My assumption is any job failure will reach the client 
processDisconnect method after the class loader is gone.

> Potential Kafka producer leak in case of failures
> -------------------------------------------------
>
>                 Key: FLINK-10455
>                 URL: https://issues.apache.org/jira/browse/FLINK-10455
>             Project: Flink
>          Issue Type: Bug
>          Components: Connectors / Kafka
>    Affects Versions: 1.5.2
>            Reporter: Nico Kruber
>            Assignee: Andrey Zagrebin
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.5.6, 1.7.0, 1.7.3, 1.9.0, 1.8.1
>
>
> If the Kafka brokers' timeout is too low for our checkpoint interval [1], we 
> may get an {{ProducerFencedException}}. Documentation around 
> {{ProducerFencedException}} explicitly states that we should close the 
> producer after encountering it.
> By looking at the code, it doesn't seem like this is actually done in 
> {{FlinkKafkaProducer011}}. Also, in case one transaction's commit in 
> {{TwoPhaseCommitSinkFunction#notifyCheckpointComplete}} fails with an 
> exception, we don't clean up (nor try to commit) any other transaction.
> -> from what I see, {{TwoPhaseCommitSinkFunction#notifyCheckpointComplete}} 
> simply iterates over the {{pendingCommitTransactions}} which is not touched 
> during {{close()}}
> Now if we restart the failing job on the same Flink cluster, any resources 
> from the previous attempt will still linger around.
> [1] 
> https://ci.apache.org/projects/flink/flink-docs-release-1.5/dev/connectors/kafka.html#kafka-011



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