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From "Radim Kolar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-4868) Allow multiple iteration for map
Date Tue, 11 Dec 2012 02:57:21 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4868?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13528630#comment-13528630
] 

Radim Kolar commented on MAPREDUCE-4868:
----------------------------------------

also this one you can find handy. org.apache.hadoop.mapred.lib.ChainMapper
                
> Allow multiple iteration for map
> --------------------------------
>
>                 Key: MAPREDUCE-4868
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4868
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: mrv2
>    Affects Versions: 3.0.0, 2.0.3-alpha
>            Reporter: Jerry Chen
>             Fix For: 3.0.0, 2.0.3-alpha
>
>   Original Estimate: 168h
>  Remaining Estimate: 168h
>
> Currently, the Mapper class allows advanced users to override "public void run(Context
context)" method for more control over the execution of the mapper, while Context interface
limit the operations over the data which is the foundation of "more control".
> One of use cases is that when I am considering a hive optimziation problem, I want to
go two passes over the input data instead of using a another job or task ( which may slower
the whole process). Each pass do the same thing but with a different parameters.
> This is a new paradigm of Map Reduce usage and can be archived easily by extend Context
interface a little with the more control over the data such as reset the input.

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