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From "Andy Konwinski (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-5182) Task processes not exiting due to ackQueue bug in DFSClient
Date Fri, 06 Feb 2009 02:31:59 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-5182?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Andy Konwinski updated HADOOP-5182:
-----------------------------------

    Attachment: jstack_ackqueue_bug

jstack output showing processes waiting on ackQueue lock

> Task processes not exiting due to ackQueue bug in DFSClient
> -----------------------------------------------------------
>
>                 Key: HADOOP-5182
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5182
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.20.0, 0.21.0
>         Environment: EC2 with Ubuntu Linux 2.6.16 AMI. Hadoop trunk revision 734915
>            Reporter: Andy Konwinski
>         Attachments: jstack_ackqueue_bug
>
>
> I was running some gridmix tests on a 10 node cluster on EC2 and ran into an issue with
unmodified Hadoop trunk revision (SVN revision#  734915). After running gridmix multiple times,
I noticed several mapreduce jobs stuck in the running state. They remained in that hung state
for several days, while other gridmixes of that size finished in approximately 8 hours, and
are still in that state actually.
> I saw that the slave nodes had a bunch of hung task processes running, for tasks that
the JobTracker log said were completed. These were hanging because the SIGTERM handler was
waiting on DFSClient to close existing streams, but this was never finishing because DFSOutputStream
waits on an ackQueue from the datanodes that was apparently getting no acks. The tasks did
finish their work, but the processes hung around.
> I'll attached a sample jstack trace - note how the SIGTERM handler is blocked on "thread-5",
which is waiting for a monitor on the DFSOutputStream, but this stream's monitor is held by
main, which is trying to flush the stream (last trace in the file).
> Has anyone seen this issue before?
> Another thing I saw was cleanup tasks never running (they are stuck in the initializing
state on the web UI and can't be seen as running processes on the nodes). Not sure if that
is actually related.

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