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From "Jothi Padmanabhan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4683) Move the call to getMapCompletionEvents in ReduceTask.ReduceCopier.fetchOutputs to a separate thread
Date Tue, 25 Nov 2008 06:21:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4683?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12650475#action_12650475
] 

Jothi Padmanabhan commented on HADOOP-4683:
-------------------------------------------

Discussed offline with Owen. While the sleep itself is one part of the problem, the more compelling
case for having a separate thread would be the case where the JobTracker is slow and the shuffle
scheduler is stuck because the actual call to getMapCompletionEvents is taking a long time
to return.

> Move the call to getMapCompletionEvents in ReduceTask.ReduceCopier.fetchOutputs to a
separate thread
> ----------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-4683
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4683
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Devaraj Das
>            Assignee: Jothi Padmanabhan
>             Fix For: 0.20.0
>
>
> The method ReduceTask.ReduceCopier.fetchOutputs makes a call to getMapCompletionEvents
every iteration of the loop. This should be moved out to a separate thread. This might slow
down the shuffle scheduler in some cases since there is a sleep inside the getMapCompletionEvents
method.

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