[jira] [Commented] (KAFKA-989) Race condition shutting down high-level consumer results in spinning background thread

["Jun Rao (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-989?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13729625#comment-13729625 ] 

Jun Rao commented on KAFKA-989:
-------------------------------

Thanks for the patch. I think it addresses one particular issue: When the consumer connector is shut down, there could still be an outstanding rebalance that uses zkclient which is already set to null. I am not sure if it addresses the problem that you hit though. Some comments:

1. Since syncedRebalance() is called in multiple places, so the shutdown lock should be checked inside syncedRebalance(). Since there is already a rebalanceLock in syncedRebalance(), perhaps shutdown() can just synchronize on that.


                
> Race condition shutting down high-level consumer results in spinning background thread
> --------------------------------------------------------------------------------------
>
>                 Key: KAFKA-989
>                 URL: https://issues.apache.org/jira/browse/KAFKA-989
>             Project: Kafka
>          Issue Type: Bug
>    Affects Versions: 0.8
>         Environment: Ubuntu Linux x64
>            Reporter: Phil Hargett
>         Attachments: KAFKA-989-failed-to-find-leader.patch, KAFKA-989-failed-to-find-leader-patch2.patch
>
>
> Running an application that uses the Kafka client under load, can often hit this issue within a few hours.
> High-level consumers come and go over this application's lifecycle, but there are a variety of defenses that ensure each high-level consumer lasts several seconds before being shutdown.  Nevertheless, some race is causing this background thread to continue long after the ZKClient it is using has been disconnected.  Since the thread was spawned by a consumer that has already been shutdown, the application has no way to find this thread and stop it.
> Reported on the users-kafka mailing list 6/25 as "0.8 throwing exception 'Failed to find leader' and high-level consumer fails to make progress". 
> The only remedy is to shutdown the application and restart it.  Externally detecting that this state has occurred is not pleasant: need to grep log for repeated occurrences of the same exception.
> Stack trace:
> Failed to find leader for Set([topic6,0]): java.lang.NullPointerException
> 	at org.I0Itec.zkclient.ZkClient$2.call(ZkClient.java:416)
> 	at org.I0Itec.zkclient.ZkClient$2.call(ZkClient.java:413)
> 	at org.I0Itec.zkclient.ZkClient.retryUntilConnected(ZkClient.java:675)
> 	at org.I0Itec.zkclient.ZkClient.getChildren(ZkClient.java:413)
> 	at org.I0Itec.zkclient.ZkClient.getChildren(ZkClient.java:409)
> 	at kafka.utils.ZkUtils$.getChildrenParentMayNotExist(ZkUtils.scala:438)
> 	at kafka.utils.ZkUtils$.getAllBrokersInCluster(ZkUtils.scala:75)
> 	at kafka.consumer.ConsumerFetcherManager$LeaderFinderThread.doWork(ConsumerFetcherManager.scala:63)
> 	at kafka.utils.ShutdownableThread.run(ShutdownableThread.scala:51)

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira