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https://issues.apache.org/jira/browse/MAPREDUCE-2094?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14075752#comment-14075752
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Hadoop QA commented on MAPREDUCE-2094:
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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/12658039/MAPREDUCE-2094-20140727-svn.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 3 new
or modified test files.
{color:green}+1 javac{color}. The applied patch does not increase the
total number of javac compiler warnings.
{color:green}+1 javadoc{color}. There were no new javadoc 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 2.0.3) 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.
{color:green}+1 contrib tests{color}. The patch passed contrib unit tests.
Test results:
https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/4772//testReport/
Console output:
https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/4772//console
This message is automatically generated.
> org.apache.hadoop.mapreduce.lib.input.FileInputFormat: isSplitable implements
> unsafe default behaviour that is different from the documented behaviour.
> -------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-2094
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-2094
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: task
> Reporter: Niels Basjes
> Assignee: Niels Basjes
> Attachments: MAPREDUCE-2094-2011-05-19.patch,
> MAPREDUCE-2094-20140727-svn.patch, MAPREDUCE-2094-20140727.patch,
> MAPREDUCE-2094-FileInputFormat-docs-v2.patch
>
>
> When implementing a custom derivative of FileInputFormat we ran into the
> effect that a large Gzipped input file would be processed several times.
> A near 1GiB file would be processed around 36 times in its entirety. Thus
> producing garbage results and taking up a lot more CPU time than needed.
> It took a while to figure out and what we found is that the default
> implementation of the isSplittable method in
> [org.apache.hadoop.mapreduce.lib.input.FileInputFormat |
> http://svn.apache.org/viewvc/hadoop/mapreduce/trunk/src/java/org/apache/hadoop/mapreduce/lib/input/FileInputFormat.java?view=markup
> ] is simply "return true;".
> This is a very unsafe default and is in contradiction with the JavaDoc of the
> method which states: "Is the given filename splitable? Usually, true, but if
> the file is stream compressed, it will not be. " . The actual implementation
> effectively does "Is the given filename splitable? Always true, even if the
> file is stream compressed using an unsplittable compression codec. "
> For our situation (where we always have Gzipped input) we took the easy way
> out and simply implemented an isSplittable in our class that does "return
> false; "
> Now there are essentially 3 ways I can think of for fixing this (in order of
> what I would find preferable):
> # Implement something that looks at the used compression of the file (i.e. do
> migrate the implementation from TextInputFormat to FileInputFormat). This
> would make the method do what the JavaDoc describes.
> # "Force" developers to think about it and make this method abstract.
> # Use a "safe" default (i.e. return false)
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