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From "Hemanth Yamijala (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1398) TaskLauncher remains stuck on tasks waiting for free nodes even if task is killed.
Date Tue, 16 Feb 2010 10:49:28 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12834157#action_12834157

Hemanth Yamijala commented on MAPREDUCE-1398:

bq. The patch did not introduce any new unsynchronized code.

I verified this. Also, per comment from Chris in MAPREDUCE-1497, IndexCache is probably already
thead-safe. Hence, this might be a legitimate case of suppressing findbugs warning. Based
on this, I think the patch is ready for commit.

> TaskLauncher remains stuck on tasks waiting for free nodes even if task is killed.
> ----------------------------------------------------------------------------------
>                 Key: MAPREDUCE-1398
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1398
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: tasktracker
>            Reporter: Hemanth Yamijala
>            Assignee: Amareshwari Sriramadasu
>             Fix For: 0.22.0
>         Attachments: patch-1398-1.txt, patch-1398-2.txt, patch-1398-ydist.txt, patch-1398.txt
> Tasks could be assigned to trackers for slots that are running other tasks in a commit
pending state. This is an optimization done to pipeline task assignment and launch. When the
task reaches the tracker, it waits until sufficient slots become free for it. This wait is
done in the TaskLauncher thread. Now, while waiting, if the task is killed externally (maybe
because the job finishes, etc), the TaskLauncher is not notified of this. So, it continues
to wait for the killed task to get sufficient slots. If slots do not become free for a long
time, this would result in considerable delay in waking up the TaskLauncher thread. If the
waiting task happens to be a high RAM task, then it is also wasteful, because by waking up,
it can make way for normal tasks that can run on the available number of slots.

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