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Posted to common-dev@hadoop.apache.org by "Robert Chansler (JIRA)" <ji...@apache.org> on 2008/10/22 00:42:44 UTC
[jira] Updated: (HADOOP-3702) add support for chaining Maps in a
single Map and after a Reduce [M*/RM*]
[ https://issues.apache.org/jira/browse/HADOOP-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Robert Chansler updated HADOOP-3702:
------------------------------------
Release Note:
Introduced ChainMapper and the ChainReducer classes to allow composing chains of Maps and Reduces in a single Map/Reduce job, something like MAP+ REDUCE MAP*.
was:
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.
> 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
> Fix For: 0.19.0
>
> Attachments: Hadoop-3702.patch, patch3702.txt, patch3702.txt, patch3702.txt, 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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