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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-1347) Missing synchronization in MultipleOutputFormat
Date Sat, 25 Jun 2011 08:38:47 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.r4.diff

New patch, with multithread case test attached.

Patch uses the utility test functions from https://issues.apache.org/jira/browse/HADOOP-7298
to test with multiple threads.

Local testing easily has the older implementation failing (every attempt, with low conflict
varience), while newer passes without a conflict.

> 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
>            Assignee: Harsh J
>         Attachments: MAPREDUCE-1347.r2.diff, MAPREDUCE-1347.r3.diff, MAPREDUCE-1347.r4.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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