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From "Harsh J Chouraria (JIRA)" <j...@apache.org>
Subject [jira] Updated: (MAPREDUCE-1347) Missing synchronization in MultipleOutputFormat
Date Fri, 25 Feb 2011 21:29:21 GMT

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

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

    Attachment: mapreduce.1347.r1.diff

Here's a patch that attempts to solve this issue.

> 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: 0.20.2, 0.21.0, 0.22.0
>            Reporter: Todd Lipcon
>         Attachments: 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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