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Posted to common-dev@hadoop.apache.org by "Owen O'Malley (JIRA)" <ji...@apache.org> on 2008/09/05 18:00:49 UTC
[jira] Commented: (HADOOP-3940) Reduce often attempts in memory
merge with no work
[ https://issues.apache.org/jira/browse/HADOOP-3940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12628660#action_12628660 ]
Owen O'Malley commented on HADOOP-3940:
---------------------------------------
There was a suggestion on the list to include this in 0.18.1. That sounds right to me. Thoughts?
> Reduce often attempts in memory merge with no work
> --------------------------------------------------
>
> Key: HADOOP-3940
> URL: https://issues.apache.org/jira/browse/HADOOP-3940
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.18.0
> Reporter: Chris Douglas
> Assignee: Chris Douglas
> Priority: Minor
> Fix For: 0.19.0
>
> Attachments: 3940-0.patch, 3940-1.patch
>
>
> ReduceTask.ReduceCopier.ShuffleRamManager initializes numRequiredMapOutputs to 0, so one of the predicates in ShuffleRamManager::waitForDataToMerge, {{numPendingRequests < numRequiredMapOutputs}}, is false until the first map output is fetched and false again after the last map output is fetched. The InMemFSMergeThread thread will loop busily in this state.
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