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Date: Tue, 1 Sep 2015 18:33:46 +0000 (UTC)
From: "Vinod Kumar Vavilapalli (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Updated] (HDFS-7763) fix zkfc hung issue due to not
 catching exception in a corner case
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     [ https://issues.apache.org/jira/browse/HDFS-7763?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vinod Kumar Vavilapalli updated HDFS-7763:
------------------------------------------
    Fix Version/s: 2.6.1

[~sjlee0] backported this to 2.6.1. I just pushed the commit to 2.6.1 after running compilation, the patch applied cleanly.

> fix zkfc hung issue due to not catching exception in a corner case
> ------------------------------------------------------------------
>
>                 Key: HDFS-7763
>                 URL: https://issues.apache.org/jira/browse/HDFS-7763
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: ha
>    Affects Versions: 2.6.0
>            Reporter: Liang Xie
>            Assignee: Liang Xie
>              Labels: 2.6.1-candidate
>             Fix For: 2.7.0, 2.6.1
>
>         Attachments: HDFS-7763-001.txt, HDFS-7763-002.txt, jstack.4936
>
>
> In our product cluster, we hit both the two zkfc process is hung after a zk network outage.
> the zkfc log said:
> {code}
> 2015-02-07,17:40:11,875 INFO org.apache.zookeeper.ClientCnxn: Client session timed out, have not heard from server in 3334ms for sessionid 0x4a61bacdd9dfb2, closing socket connection and attempting reconnect
> 2015-02-07,17:40:11,977 FATAL org.apache.hadoop.ha.ActiveStandbyElector: Received stat error from Zookeeper. code:CONNECTIONLOSS. Not retrying further znode monitoring connection errors.
> 2015-02-07,17:40:12,425 INFO org.apache.zookeeper.ZooKeeper: Session: 0x4a61bacdd9dfb2 closed
> 2015-02-07,17:40:12,425 FATAL org.apache.hadoop.ha.ZKFailoverController: Fatal error occurred:Received stat error from Zookeeper. code:CONNECTIONLOSS. Not retrying further znode monitoring connection errors.
> 2015-02-07,17:40:12,425 INFO org.apache.hadoop.ipc.Server: Stopping server on 11300
> 2015-02-07,17:40:12,425 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 WARN org.apache.hadoop.ha.ActiveStandbyElector: Ignoring stale result from old client with sessionId 0x4a61bacdd9dfb2
> 2015-02-07,17:40:12,426 INFO org.apache.zookeeper.ClientCnxn: EventThread shut down
> 2015-02-07,17:40:12,426 INFO org.apache.hadoop.ha.ActiveStandbyElector: Yielding from election
> 2015-02-07,17:40:12,426 INFO org.apache.hadoop.ipc.Server: Stopping IPC Server Responder
> 2015-02-07,17:40:12,426 INFO org.apache.hadoop.ha.HealthMonitor: Stopping HealthMonitor thread
> 2015-02-07,17:40:12,426 INFO org.apache.hadoop.ipc.Server: Stopping IPC Server listener on 11300
> {code}
> and the thread dump also be uploaded as attachment.
> From the dump, we can see due to the unknown non-daemon threads(pool-*-thread-*), the process did not exit, but the critical threads, like health monitor and rpc threads had been stopped, so our watchdog(supervisord) had not not observed the zkfc process is down or abnormal.  so the following namenode failover could not be done as expected.
> there're two possible fixes here, 1) figure out the unset-thread-name, like pool-7-thread-1, where them came from and close or set daemon property. i tried to search but got nothing right now. 2) catch the exception from ZKFailoverController.run() so we can continue to exec the System.exit, the attached patch is 2).


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