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From "Alejandro Abdelnur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1230) Replace parameters with context objects in Mapper, Reducer, Partitioner, InputFormat, and OutputFormat classes
Date Wed, 06 Aug 2008 11:46:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12620218#action_12620218
] 

Alejandro Abdelnur commented on HADOOP-1230:
--------------------------------------------

Got the right code. 

Yes, I can see how with the current API option #1 is simpler to implement. 

I'm not sure of option #2 with with the current API, it would be error prone if the developer
implements the wrong signature.

What I liked about option #2 was the fact the multiple-outputs were done to the Context as
the standard-output. With the API in the patch I was looking at that was possible as the Context
was parameterized as generic.


On a side note, what is the value of having a inner {{Mapper.Context}} just extending {{MapContext}}
(and the same for {{Reducer}}) but no adding any methods? Wouldn't be simpler just to use
directly the {{MapContext}} in the {{Mapper}} methods signature (similarly in the {{Reducer}})
?




> Replace parameters with context objects in Mapper, Reducer, Partitioner, InputFormat,
and OutputFormat classes
> --------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-1230
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1230
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>            Reporter: Owen O'Malley
>            Assignee: Owen O'Malley
>         Attachments: context-objs-2.patch, context-objs-3.patch, context-objs.patch
>
>
> This is a big change, but it will future-proof our API's. To maintain backwards compatibility,
I'd suggest that we move over to a new package name (org.apache.hadoop.mapreduce) and deprecate
the old interfaces and package. Basically, it will replace:
> package org.apache.hadoop.mapred;
> public interface Mapper extends JobConfigurable, Closeable {
>   void map(WritableComparable key, Writable value, OutputCollector output, Reporter reporter)
throws IOException;
> }
> with:
> package org.apache.hadoop.mapreduce;
> public interface Mapper extends Closable {
>   void map(MapContext context) throws IOException;
> }
> where MapContext has the methods like getKey(), getValue(), collect(Key, Value), progress(),
etc.

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