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https://issues.apache.org/jira/browse/HADOOP-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12619814#action_12619814
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Alejandro Abdelnur commented on HADOOP-3702:
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*On #1*, Yes but this introduces a backwards incompatibility as there is code
out there (outside of core) that uses the {{write(OutputStream)}} with
{{DataOuputStream}} instances and the change is breaking such usages (as the
previous patch found).
*On #2*, I'm missing something here, under what circumstances would it make
sense to use the {{Chain*}} classes with generics that would be checked at
compile time? If it is just a way of avoiding the @SuppressWarnings annotations
I'd prefer the anotations as, IMO, they are meant for this cases.
> add support for chaining Maps in a single Map and after a Reduce [M*/RM*]
> -------------------------------------------------------------------------
>
> Key: HADOOP-3702
> URL: https://issues.apache.org/jira/browse/HADOOP-3702
> Project: Hadoop Core
> Issue Type: New Feature
> Components: mapred
> Environment: all
> Reporter: Alejandro Abdelnur
> Assignee: Alejandro Abdelnur
> Attachments: patch3702.txt, patch3702.txt, patch3702.txt,
> patch3702.txt, patch3702.txt, patch3702.txt, patch3702.txt, patch3702.txt,
> patch3702.txt, patch3702.txt
>
>
> On the same input, we usually need to run multiple Maps one after the other
> without no Reduce. We also have to run multiple Maps after the Reduce.
> If all pre-Reduce Maps are chained together and run as a single Map a
> significant amount of Disk I/O will be avoided.
> Similarly all post-Reduce Maps can be chained together and run in the Reduce
> phase after the Reduce.
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