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From "Alejandro Abdelnur (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-3702) add support for chaining Maps in a single Map and after a Reduce [M*/RM*]
Date Thu, 10 Jul 2008 07:23:31 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Alejandro Abdelnur updated HADOOP-3702:
---------------------------------------

    Release Note: 
The ChainMapper and the ChainReducer classes allow composing chains of Maps and Reduces in
a single Map/Reduce job, something like MAP+ / REDUCE MAP*.
An immediate benefit of this pattern is reduction in disk IO as many Maps can be club together
in a single job.

          Status: Patch Available  (was: Open)

Proposed implementation. Different from the initial comment, it uses a JobConf to configure
the Maps in the Chain.

> 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
>            Priority: Minor
>         Attachments: 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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