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https://issues.apache.org/jira/browse/MAPREDUCE-2001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13477585#comment-13477585
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liu yu commented on MAPREDUCE-2001:
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When you watch the problem, you need to check your reduce.
It should be 'Iterable<VALUEIN>',not 'Iterator<VALUEIN>'.
The latter won't rewrite the mothed reduce(...) of Reducer.
> Enhancement to SequenceFileOutputFormat to allow user to set MetaData
> ---------------------------------------------------------------------
>
> Key: MAPREDUCE-2001
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-2001
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Affects Versions: 0.20.2
> Reporter: David Rosenstrauch
> Priority: Minor
> Attachments: MAPREDUCE-2001.patch
>
>
> The org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat class
> currently does not provide a way for the user to pass in a MetaData object to
> be written to the SequenceFile.
> Currently he only way for a developer to implement this functionality appears
> to be to create a subclass which overrides the SequenceFileOutputFormat's
> getRecordWriter() method, which is a bit of a kludge.
> This seems to be a common enough request to warrant a fix of some sort.
> (It's already been brought up twice in the past year:
> http://www.mail-archive.com/[email protected]/msg02198.html and
> http://www.mail-archive.com/[email protected]/msg00904.html)
> A couple of possible solutions:
> 1) provide a static method SequenceFileOutputFormat.setMetaData(Job, MetaData)
> 2) Provide a (non-static) setMetaData() method on the
> SequenceFileOutputFormat class. The user would create a subclass of
> SequenceFileOutputFormat which, say, implements Configurable. Then in the
> setConf() method, the user could create the MetaData object (using data from
> the Configuration), and then call setMetaData. The SequenceFileOutputFormat
> would then use this MetaData object when creating the SequenceFile. (Note
> that the user would have to create a subclass of SequenceFileOutputFormat to
> make this solution work.)
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