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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-3310) Custom grouping comparator cannot be set for Combiners
Date Fri, 15 Nov 2013 02:57:22 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-3310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13823238#comment-13823238

Hadoop QA commented on MAPREDUCE-3310:

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  against trunk revision .

    {color:green}+1 @author{color}.  The patch does not contain any @author tags.

    {color:green}+1 tests included{color}.  The patch appears to include 2 new or modified
test files.

      {color:red}-1 javac{color}.  The applied patch generated 1546 javac compiler warnings
(more than the trunk's current 1545 warnings).

    {color:green}+1 javadoc{color}.  The javadoc tool did not generate any warning messages.

    {color:green}+1 eclipse:eclipse{color}.  The patch built with eclipse:eclipse.

    {color:green}+1 findbugs{color}.  The patch does not introduce any new Findbugs (version
1.3.9) warnings.

    {color:green}+1 release audit{color}.  The applied patch does not increase the total number
of release audit warnings.

    {color:red}-1 core tests{color}.  The patch failed these unit tests in hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core


    {color:green}+1 contrib tests{color}.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/4200//testReport/
Javac warnings: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/4200//artifact/trunk/patchprocess/diffJavacWarnings.txt
Console output: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/4200//console

This message is automatically generated.

> Custom grouping comparator cannot be set for Combiners
> ------------------------------------------------------
>                 Key: MAPREDUCE-3310
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3310
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: client
>    Affects Versions: 0.20.1
>         Environment: All
>            Reporter: Mathias Herberts
>            Assignee: Alejandro Abdelnur
>         Attachments: MAPREDUCE-3310-trunk.patch
> Combiners are often described as 'Reducers running on the Map side'.
> As Reducers, Combiners are fed <K,{V}>, where {V} is built by grouping values associated
with the 'same' key.
> For Reducers, the comparator used for grouping values can be set independently of that
used to sort the keys (using Job.setGroupingComparatorClass).
> Such a configuration is not possible for Combiners, meaning some things done in Reducers
cannot be done in Combiners (such as secondary sort).
> It would be handy to have a Job.setCombinerGroupingComparatorClass method that would
allow the setting of the grouping comparator used when applying a Combiner.

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