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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, 22 Jul 2008 14:41:31 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12615633#action_12615633
] 

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

Thanks for the feedback.

*On "each stage in the pipeline having its own configuration .. put them into the outer configuration":*

The use case is that mappers/reducer in the chain (I'm not using 'pipe' to avoid confusion
as it has other use in Hadoop) are not aware of each other, and that they are in a chain,
and they may have collision in the configuration keys they use. 

*On "If you are going to do that, ... make Configuration Writable and use the writable stringifier?":*

That was my initial idea but it would have required changes in the Configuration and I was
avoiding any change in the core.

I'll make this change.

*On "use {{hadoop.io.Data{In,Out}putBuffer}} ...":*

I'll look at it.

*On "You should probably convert the task id string to a TaskAttemptID ...":*

OK

*On "preferred sytle is Sun's":*

OK
 

> 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, 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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