[jira] [Commented] (MAPREDUCE-4228) mapreduce.job.reduce.slowstart.completedmaps is not working properly to delay the scheduling of the reduce tasks

["Hadoop QA (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13398968#comment-13398968 ] 

Hadoop QA commented on MAPREDUCE-4228:
--------------------------------------

-1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12532955/MAPREDUCE-4228.patch
  against trunk revision .

    +1 @author.  The patch does not contain any @author tags.

    +1 tests included.  The patch appears to include 1 new or modified test files.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    -1 javadoc.  The javadoc tool appears to have generated 13 warning messages.

    +1 eclipse:eclipse.  The patch built with eclipse:eclipse.

    +1 findbugs.  The patch does not introduce any new Findbugs (version 1.3.9) warnings.

    +1 release audit.  The applied patch does not increase the total number of release audit warnings.

    +1 core tests.  The patch passed unit tests in hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app.

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/2494//testReport/
Console output: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/2494//console

This message is automatically generated.
                
> mapreduce.job.reduce.slowstart.completedmaps is not working properly to delay the scheduling of the reduce tasks
> ----------------------------------------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-4228
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4228
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: applicationmaster, mrv2
>    Affects Versions: 0.23.1
>            Reporter: Jason Lowe
>            Assignee: Jason Lowe
>         Attachments: MAPREDUCE-4228.patch, MAPREDUCE-4228.patch, MAPREDUCE-4228.patch
>
>
> If no more map tasks need to be scheduled but not all have completed, the ApplicationMaster will start scheduling reducers even if the number of completed maps has not met the mapreduce.job.reduce.slowstart.completedmaps threshold.  For example, if the property is set to 1.0 all maps should complete before any reducers are scheduled.  However the reducers are scheduled as soon as the last map task is assigned to a container.  For a job with very long-running maps, a cluster with enough capacity to launch all map tasks could cause reducers to launch prematurely and waste cluster resources.
> Thanks to Phil Su for discovering this issue.

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