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