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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-1347) Missing synchronization in MultipleOutputFormat
Date Tue, 19 Jul 2011 13:19:58 GMT

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

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

    Status: In Progress  (was: Patch Available)

Oh oops, forgot about the blocker. Marking as in-progress.

> 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: 0.21.0, 0.20.2, 0.22.0
>            Reporter: Todd Lipcon
>            Assignee: Harsh J
>             Fix For: 0.23.0
>
>         Attachments: MAPREDUCE-1347.r2.diff, MAPREDUCE-1347.r3.diff, MAPREDUCE-1347.r4.diff,
MAPREDUCE-1347.r5.diff, MAPREDUCE-1347.r6.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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