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Posted to mapreduce-issues@hadoop.apache.org by "Harsh J (JIRA)" <ji...@apache.org> on 2012/12/02 06:08:00 UTC
[jira] [Commented] (MAPREDUCE-1347) Missing synchronization in
MultipleOutputFormat
[ https://issues.apache.org/jira/browse/MAPREDUCE-1347?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13508167#comment-13508167 ]
Harsh J commented on MAPREDUCE-1347:
------------------------------------
Patch still applies cleanly to trunk. Any further comments atop jenkins' +1?
> Missing synchronization in MultipleOutputFormat
> -----------------------------------------------
>
> Key: MAPREDUCE-1347
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1347
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: client
> Affects Versions: 1.0.0
> Reporter: Todd Lipcon
> Assignee: Harsh J
> Labels: concurrency
> 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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