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https://issues.apache.org/jira/browse/MAPREDUCE-2047?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Allen Wittenauer resolved MAPREDUCE-2047.
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Resolution: Incomplete
Spec exec got a major overhaul since then. Closing this as stale.
> reduce overhead of findSpeculativeTask
> --------------------------------------
>
> Key: MAPREDUCE-2047
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-2047
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: jobtracker
> Environment: hadoop-20 with HADOOP-2141
> Reporter: Joydeep Sen Sarma
> Assignee: Joydeep Sen Sarma
> Attachments: 2047.3.patch, mapreduce-2047.1.patch,
> mapreduce-2047.2.patch
>
>
> We are bottlenecked (in the JT) on the jobtracker lock and calls to
> findSpeculativeTask frequently show up as one of the top routines (by time)
> called holding this lock.
> this routine calls canBeSpeculated() and hasRunOnMachine() for each task in a
> candidate job. Both these routines are reasonably expensive when invoked
> repeatedly for thousands of tasks. The top candidates for speculation from a
> job only need to be refreshed periodically (and not once every heartbeat) -
> and we can can avoid most of these invocations this way.
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