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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-1347) Missing synchronization in MultipleOutputFormat
Date Sun, 07 Oct 2012 13:04:03 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-1347?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Harsh J updated MAPREDUCE-1347:
-------------------------------

    Attachment: MAPREDUCE-1347.r10.diff

New patch that removes the MapMaker API of Guava and moves to the CacheBuilder, to avoid the
deprecation warning.
                
> 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.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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