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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-1347) Missing synchronization in MultipleOutputFormat
Date Mon, 28 May 2012 05:20:24 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1347?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13284291#comment-13284291
] 

Harsh J commented on MAPREDUCE-1347:
------------------------------------

bq. -1 javac. The applied patch generated 1934 javac compiler warnings (more than the trunk's
current 1933 warnings).

Will investigate and fix this for the current patch. Most likely may be a now-deprecated use
of APIs.
                
> Missing synchronization in MultipleOutputFormat
> -----------------------------------------------
>
>                 Key: MAPREDUCE-1347
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1347
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>    Affects Versions: 1.0.0
>            Reporter: Todd Lipcon
>            Assignee: Harsh J
>         Attachments: 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, mapreduce.1347.r1.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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