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From "Jim Donofrio (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-2001) Enhancement to SequenceFileOutputFormat to allow user to set MetaData
Date Mon, 07 May 2012 13:04:49 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13269586#comment-13269586
] 

Jim Donofrio commented on MAPREDUCE-2001:
-----------------------------------------

{noformat}
    if (numReduceTasks > 0) {
      collector = new MapOutputBuffer(umbilical, job, reporter);
    } else { 
      collector = new DirectMapOutputCollector(umbilical, job, reporter);
    }
    MapRunnable<INKEY,INVALUE,OUTKEY,OUTVALUE> runner =
      ReflectionUtils.newInstance(job.getMapRunnerClass(), job);
{noformat}

Could you give an example of what user code would break if we moved ReflectionUtils.newInstance(job.getMapRunnerClass(),
job); above if (numReduceTasks > 0) { ? Why would the configure method of the mapper care
if the recordwriter/outputformat had been created yet? I would think we would want the recordwriter/outputformat
to get configured after the configure method to allow tasks to make task level config changes
to a recordwriter/outputformat

> I imagine this working in a much better way. For new API users, they may still be able
to sneak in changes per map/reduce task, and otherwise (on Old API) rely on driver to provide
these up.

I am confused by this comment, do you agree with my approach or are you just disappointed
that the behavior will be inconsistent between the old and new api for map only jobs?
                
> 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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