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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-2001) Enhancement to SequenceFileOutputFormat to allow user to set MetaData
Date Mon, 07 May 2012 15:34:50 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13269698#comment-13269698
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Harsh J commented on MAPREDUCE-2001:
------------------------------------

bq. Why would the configure method of the mapper care if the recordwriter/outputformat had
been created yet?

It doesn't care on its own, but advanced users may be relying on this 'behavior' to do stuff.
For instance, I've once relied on this behavior to have my output format inject a few strings
into jobconf upon RW instantiation (some logic dependent on input format initialization that
goes even before this), such that I then get the set strings in my mapper's configure. True
that I was probably doing something wrong, and what I did can be done in a better/alternate
way, but I ended up relying on that behavior and thats what I'm talking about (in terms of
breakage).

bq. 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

True. I just don't know why its this way in the old API. Probably an oversight.

bq. 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?

Sorry for the confusion. Its just the latter. I agree with your approach.
                
> 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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