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From "Amar Kamat (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-762) Task's process trees may not be killed if a TT is restarted
Date Thu, 16 Jul 2009 07:31:14 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-762?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12731844#action_12731844

Amar Kamat commented on MAPREDUCE-762:

bq. I am not sure about this. So, this will be done like in the finally block of the Child
by sending a kill -pid to itself ?
Yeah. Just before the child commits suicide.

bq. What's the structure under TaskTracker.SUBDIR/pid ?
The structure would be jvm-id.pid and it would contain _user-name_, _pid_ and _start-time_
of the child process. username is required for permissions while start-time is required to
be sure that the process has not changed.

bq. We should just follow the path of TaskController.killTaskJVM - that will ensure it will
work for all task controllers. Setting permissions to 600 for the pid files owned by TT should
be fine.
Yeah. TaskController.killTask() would be invoked which will do the forceful exit of the process.

> Task's process trees may not be killed if a TT is restarted
> -----------------------------------------------------------
>                 Key: MAPREDUCE-762
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-762
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>            Reporter: Hemanth Yamijala
> Some work has been done to make sure the tasktrackers kill process trees of tasks when
they finish (either successfully, or with failures or when they are killed). Related JIRAs
are HADOOP-2721, HADOOP-5488 and HADOOP-5420. But when TTs are restarted, we do not handle
killing of process trees - though tasks will themselves die on re-establishing contact with
the TT.

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