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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-1347) Missing synchronization in MultipleOutputFormat
Date Sun, 07 Oct 2012 14:04:03 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1347?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13471248#comment-13471248
] 

Hadoop QA commented on MAPREDUCE-1347:
--------------------------------------

{color:green}+1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12548160/MAPREDUCE-1347.r10.diff
  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 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/2913//testReport/
Console output: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/2913//console

This message is automatically generated.
                
> Missing synchronization in MultipleOutputFormat
> -----------------------------------------------
>
>                 Key: MAPREDUCE-1347
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1347
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: client
>    Affects Versions: 1.0.0
>            Reporter: Todd Lipcon
>            Assignee: Harsh J
>              Labels: concurrency
>         Attachments: MAPREDUCE-1347.r10.diff, mapreduce.1347.r1.diff, MAPREDUCE-1347.r2.diff,
MAPREDUCE-1347.r3.diff, MAPREDUCE-1347.r4.diff, MAPREDUCE-1347.r5.diff, MAPREDUCE-1347.r6.diff,
MAPREDUCE-1347.r7.diff, MAPREDUCE-1347.r8.diff, MAPREDUCE-1347.r9.diff
>
>
> MultipleOutputFormat's RecordWriter implementation doesn't use synchronization when accessing
the recordWriters member. When using multithreaded mappers or reducers, this can result in
problems where two threads will both try to create the same file, causing AlreadyBeingCreatedException.
Doing this more fine-grained than just synchronizing the whole method is probably a good idea,
so that multithreaded mappers can actually achieve parallelism writing into separate output
streams.
> From what I can tell, the new API's MultipleOutputs seems not to have this issue.

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