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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2131) Speculative execution should be allowed for reducers only
Date Thu, 10 Jan 2008 02:34:34 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2131?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12557519#action_12557519
] 

Hadoop QA commented on HADOOP-2131:
-----------------------------------

+1 overall.  Here are the results of testing the latest attachment 
http://issues.apache.org/jira/secure/attachment/12372739/patch-2131.txt
against trunk revision r610603.

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

    javadoc +1.  The javadoc tool did not generate any warning messages.

    javac +1.  The applied patch does not generate any new compiler warnings.

    findbugs +1.  The patch does not introduce any new Findbugs warnings.

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

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

Test results: http://lucene.zones.apache.org:8080/hudson/job/Hadoop-Patch/1533/testReport/
Findbugs warnings: http://lucene.zones.apache.org:8080/hudson/job/Hadoop-Patch/1533/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Checkstyle results: http://lucene.zones.apache.org:8080/hudson/job/Hadoop-Patch/1533/artifact/trunk/build/test/checkstyle-errors.html
Console output: http://lucene.zones.apache.org:8080/hudson/job/Hadoop-Patch/1533/console

This message is automatically generated.

> Speculative execution should be allowed for reducers only
> ---------------------------------------------------------
>
>                 Key: HADOOP-2131
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2131
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: mapred
>         Environment: Hadoop job, map fetches data from external systems
>            Reporter: Srikanth Kakani
>            Assignee: Amareshwari Sri Ramadasu
>            Priority: Critical
>             Fix For: 0.16.0
>
>         Attachments: patch-2131.txt, patch-2131.txt, patch-2131.txt
>
>
> Consider hadoop jobs where maps fetch data from external systems, and emit the data.
The reducers in this are identity reducers. The data processed by these jobs is huge. There
could be slow nodes in this cluster and some of the reducers run twice as slow as their counterparts.
This could result in a long tail. Speculative execution would help greatly in such cases.
However given the current hadoop, we have to select speculative execution for both maps and
reducers. In this case hurting the map performance as they are fetching data from external
systems thereby overloading the external systems.
> Speculative execution only on reducers would be a great way to solve this problem.

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