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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4018) limit memory usage in jobtracker
Date Thu, 04 Sep 2008 06:38:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4018?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12628266#action_12628266
] 

dhruba borthakur commented on HADOOP-4018:
------------------------------------------

I think the goal is to avoid making the JobTracker allocate memory for tasks for a job that
causes the limit to exceed a certain quantity. if the limit-check is in the scheduler, all
schedulers have to implement this check. Also, by the time the scheduler gets to look at the
task, the JT might have already allocated some memory for some task-related status.

I am assuming that it is better to check this in the JT rather than in the scheduler, but
please let me know if my assumption seems invalid.

> limit memory usage in jobtracker
> --------------------------------
>
>                 Key: HADOOP-4018
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4018
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: maxSplits.patch, maxSplits2.patch, maxSplits3.patch, maxSplits4.patch,
maxSplits5.patch, maxSplits6.patch
>
>
> We have seen instances when a user submitted a job with many thousands of mappers. The
JobTracker was running with 3GB heap, but it was still not enough to prevent memory trashing
from Garbage collection; effectively the Job Tracker was not able to serve jobs and had to
be restarted.
> One simple proposal would be to limit the maximum number of tasks per job. This can be
a configurable parameter. Is there other things that eat huge globs of memory in job Tracker?

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