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https://issues.apache.org/jira/browse/HADOOP-968?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12489511
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Doug Cutting commented on HADOOP-968:
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I think David's point was that it would be best to fix the metrics code so that
its thread *is* a daemon thread, rather than to expect client code to
explicitly stop that thread.
> Reduce shuffle and merge should be done a child JVM
> ---------------------------------------------------
>
> Key: HADOOP-968
> URL: https://issues.apache.org/jira/browse/HADOOP-968
> Project: Hadoop
> Issue Type: Improvement
> Components: mapred
> Affects Versions: 0.10.1
> Reporter: Owen O'Malley
> Assigned To: Devaraj Das
> Fix For: 0.13.0
>
> Attachments: 968-reindent.patch, 968-with-metrics-fix.patch,
> 968.apr06.patch, 968.apr10.patch, 968.apr14.patch, 968.apr14.patch, 968.patch
>
>
> The Reduce's shuffle and initial merge is done in the TaskTracker's JVM. It
> would be better to have it run in the Task's child JVM. The advantages are:
> 1. The class path and environment would be set up correctly.
> 2. User code doesn't need to be loaded into the TaskTracker.
> 3. Lower memory usage and contention in the TaskTracker.
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