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From "liu yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-2001) Enhancement to SequenceFileOutputFormat to allow user to set MetaData
Date Wed, 17 Oct 2012 04:02:04 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13477585#comment-13477585
] 

liu yu commented on MAPREDUCE-2001:
-----------------------------------

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/common-user@hadoop.apache.org/msg02198.html
and http://www.mail-archive.com/mapreduce-user@hadoop.apache.org/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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