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From "Alejandro Abdelnur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3702) add support for chaining Maps in a single Map and after a Reduce [M*/RM*]
Date Tue, 05 Aug 2008 08:50:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12619814#action_12619814
] 

Alejandro Abdelnur commented on HADOOP-3702:
--------------------------------------------

*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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