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Hadoop QA commented on MAPREDUCE-2094: -------------------------------------- \\ \\ | (x) *{color:red}-1 overall{color}* | \\ \\ || Vote || Subsystem || Runtime || Comment || | {color:blue}0{color} | pre-patch | 14m 57s | Pre-patch trunk compilation is healthy. | | {color:green}+1{color} | @author | 0m 0s | The patch does not contain any @author tags. | | {color:green}+1{color} | tests included | 0m 0s | The patch appears to include 3 new or modified test files. | | {color:green}+1{color} | javac | 7m 40s | There were no new javac warning messages. | | {color:green}+1{color} | javadoc | 9m 47s | There were no new javadoc warning messages. | | {color:green}+1{color} | release audit | 0m 23s | The applied patch does not increase the total number of release audit warnings. | | {color:green}+1{color} | checkstyle | 0m 53s | There were no new checkstyle issues. | | {color:red}-1{color} | whitespace | 0m 0s | The patch has 1 line(s) that end in whitespace. Use git apply --whitespace=fix. | | {color:green}+1{color} | install | 1m 31s | mvn install still works. | | {color:green}+1{color} | eclipse:eclipse | 0m 34s | The patch built with eclipse:eclipse. | | {color:green}+1{color} | findbugs | 1m 16s | The patch does not introduce any new Findbugs (version 2.0.3) warnings. | | {color:green}+1{color} | mapreduce tests | 1m 38s | Tests passed in hadoop-mapreduce-client-core. | | | | 38m 46s | | \\ \\ || Subsystem || Report/Notes || | Patch URL | http://issues.apache.org/jira/secure/attachment/12730617/MAPREDUCE-2094-2015-05-05-2328.patch | | Optional Tests | javadoc javac unit findbugs checkstyle | | git revision | trunk / 0100b15 | | whitespace | https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5648/artifact/patchprocess/whitespace.txt | | hadoop-mapreduce-client-core test log | https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5648/artifact/patchprocess/testrun_hadoop-mapreduce-client-core.txt | | Test Results | https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5648/testReport/ | | Java | 1.7.0_55 | | uname | Linux asf904.gq1.ygridcore.net 3.13.0-36-lowlatency #63-Ubuntu SMP PREEMPT Wed Sep 3 21:56:12 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux | | Console output | https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5648/console | This message was 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-fixed-spaces.patch, > MAPREDUCE-2094-20140727-svn.patch, MAPREDUCE-2094-20140727.patch, > MAPREDUCE-2094-2015-05-05-2328.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) -- This message was sent by Atlassian JIRA (v6.3.4#6332)