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From "Randall Hauch (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-6252) A metric named 'XX' already exists, can't register another one.
Date Wed, 29 Nov 2017 00:08:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-6252?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16269781#comment-16269781

Randall Hauch commented on KAFKA-6252:

This also happens when a connector does not properly implement {{stop()}}. 

Connect will call {{stop()}} on a source task to signal that it should "_stop trying to poll
for new data 
and interrupt any outstanding poll() requests_" (see the [JavaDoc|http://kafka.apache.org/10/javadoc/org/apache/kafka/connect/source/SourceTask.html#stop--]
for this method).

Unfortunately, not all connectors properly adhere to this expectation. Since the metrics for
the source task are cleaned up only when the worker source task's thread completes, a task
whose {{poll()}} method blocks forever will current prevent its thread from completing. So,
we need to change how the metrics are cleaned up to ensure this always happens.

> A metric named 'XX' already exists, can't register another one.
> ---------------------------------------------------------------
>                 Key: KAFKA-6252
>                 URL: https://issues.apache.org/jira/browse/KAFKA-6252
>             Project: Kafka
>          Issue Type: Bug
>          Components: KafkaConnect
>    Affects Versions: 1.0.0
>         Environment: Linux
>            Reporter: Alexis Sellier
> When a connector crashes, It cannot be restarted and an exception like this is thrown

> {code:java}
> java.lang.IllegalArgumentException: A metric named 'MetricName [name=offset-commit-max-time-ms,
group=connector-task-metrics, description=The maximum time in milliseconds taken by this task
to commit offsets., tags={connector=hdfs-sink-connector-recover, task=0}]' already exists,
can't register another one.
> 	at org.apache.kafka.common.metrics.Metrics.registerMetric(Metrics.java:532)
> 	at org.apache.kafka.common.metrics.Sensor.add(Sensor.java:256)
> 	at org.apache.kafka.common.metrics.Sensor.add(Sensor.java:241)
> 	at org.apache.kafka.connect.runtime.WorkerTask$TaskMetricsGroup.<init>(WorkerTask.java:328)
> 	at org.apache.kafka.connect.runtime.WorkerTask.<init>(WorkerTask.java:69)
> 	at org.apache.kafka.connect.runtime.WorkerSinkTask.<init>(WorkerSinkTask.java:98)
> 	at org.apache.kafka.connect.runtime.Worker.buildWorkerTask(Worker.java:449)
> 	at org.apache.kafka.connect.runtime.Worker.startTask(Worker.java:404)
> 	at org.apache.kafka.connect.runtime.distributed.DistributedHerder.startTask(DistributedHerder.java:852)
> 	at org.apache.kafka.connect.runtime.distributed.DistributedHerder.access$1600(DistributedHerder.java:108)
> 	at org.apache.kafka.connect.runtime.distributed.DistributedHerder$13.call(DistributedHerder.java:866)
> 	at org.apache.kafka.connect.runtime.distributed.DistributedHerder$13.call(DistributedHerder.java:862)
> 	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> 	at java.lang.Thread.run(Thread.java:745)
> {code}
> I guess it's because the function taskMetricsGroup.close is not call in all the cases

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