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https://issues.apache.org/jira/browse/MAPREDUCE-4892?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13588579#comment-13588579
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Hadoop QA commented on MAPREDUCE-4892:
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{color:green}+1 overall{color}. Here are the results of testing the latest
attachment
http://issues.apache.org/jira/secure/attachment/12571219/MAPREDUCE-4892.1.alt.patch
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 1 new
or modified test files.
{color:green}+1 tests included appear to have a timeout.{color}
{color:green}+1 javac{color}. The applied patch does not increase the
total number of javac compiler 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:green}+1 core tests{color}. The patch passed unit tests in
hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core
hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient.
{color:green}+1 contrib tests{color}. The patch passed contrib unit tests.
Test results:
https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/3369//testReport/
Console output:
https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/3369//console
This message is automatically generated.
> CombineFileInputFormat node input split can be skewed on small clusters
> -----------------------------------------------------------------------
>
> Key: MAPREDUCE-4892
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4892
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Bikas Saha
> Assignee: Bikas Saha
> Fix For: 3.0.0
>
> Attachments: MAPREDUCE-4892.1.alt.patch, MAPREDUCE-4892.1.alt.patch,
> MAPREDUCE-4892.1.patch
>
>
> The CombineFileInputFormat split generation logic tries to group blocks by
> node in order to create splits. It iterates through the nodes and creates
> splits on them until there aren't enough blocks left on a node that can be
> grouped into a valid split. If the first few nodes have a lot of blocks on
> them then they can end up getting a disproportionately large share of the
> total number of splits created. This can result in poor locality of maps.
> This problem is likely to happen on small clusters where its easier to create
> a skew in the distribution of blocks on nodes.
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