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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1797) The JobTracker lock can be a reader/writer lock
Date Wed, 19 May 2010 05:52:55 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1797?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12869007#action_12869007
] 

Arun C Murthy commented on MAPREDUCE-1797:
------------------------------------------

A read-write lock in the JobTracker doesn't really make much of a difference, because the
vast majority of the operations on a JobInProgress (mostly during heartbeat processing) will
need the write lock.

OTOH, the scenario you describe with a client calling getCounter() is already fixed with MAPREDUCE-1354.

> The JobTracker lock can be a reader/writer lock
> -----------------------------------------------
>
>                 Key: MAPREDUCE-1797
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1797
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: jobtracker
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>
> The Jobtracker has a global lock and a per-job JobInProgress lock. The aim for the JobInprogress
lock is to support the ability to lock a single job's metadata without  blocking out the entire
JobTracker. However, many code paths acquire the JobTracker lock and then acquire the JobInProgress
lock while keeping the JobTracker lock. This somewhat defeats the benefit of having a per-job
lock.

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