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Posted to common-dev@hadoop.apache.org by "Chris Douglas (JIRA)" <ji...@apache.org> on 2008/08/13 00:19:44 UTC

[jira] Issue Comment Edited: (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=12622004#action_12622004 ] 

chris.douglas edited comment on HADOOP-3940 at 8/12/08 3:19 PM:
----------------------------------------------------------------

[ edit - nevermind ]

      was (Author: chris.douglas):
    Alternatively, I think this could equivalently wait on {{numPendingRequests <= numRequiredMapOutputs}}, relying on close to signal the last merge
  
> 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
>            Reporter: Chris Douglas
>            Priority: Minor
>         Attachments: 3940-0.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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