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Date: Fri, 12 Feb 2010 23:04:28 +0000 (UTC)
From: "Owen O'Malley (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Subject: [jira] Commented: (MAPREDUCE-326) The lowest level map-reduce APIs
 should be byte oriented
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    [ https://issues.apache.org/jira/browse/MAPREDUCE-326?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12833230#action_12833230 ] 

Owen O'Malley commented on MAPREDUCE-326:
-----------------------------------------

I have reservations about doubling the width of the *public* API by having both a raw and object level APIs. That will make a much much harder problem to guarantee compatibility and still enable us to make improvements to the sort and shuffle.

It is a software engineering truism that if you can accomplish something in library code, it is much better to do so rather than the framework. So instead of making a new lower level API, I'd propose layering your API on top of the object API. 

So my proposal would be:

* All types (map input key and value, map output key and value, and reduce output key and value) as ByteBuffer.
* Add a new method in the MapContext that takes write(int partition, KEYOUT key, VALUEOUT value);
* Define a new class-based serialization that handles ByteBuffer input/output.
* There are already sequence file input/output formats that deal with binary (SequenceFileAsBinary{Input|Output}Format)

With the context object API, the run method gets complete control and with the extra write method, it would be easy to add new map/reduce APIs on top.

> The lowest level map-reduce APIs should be byte oriented
> --------------------------------------------------------
>
>                 Key: MAPREDUCE-326
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-326
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>            Reporter: eric baldeschwieler
>         Attachments: MAPREDUCE-326-api.patch, MAPREDUCE-326.pdf
>
>
> As discussed here:
> https://issues.apache.org/jira/browse/HADOOP-1986#action_12551237
> The templates, serializers and other complexities that allow map-reduce to use arbitrary types complicate the design and lead to lots of object creates and other overhead that a byte oriented design would not suffer.  I believe the lowest level implementation of hadoop map-reduce should have byte string oriented APIs (for keys and values).  This API would be more performant, simpler and more easily cross language.
> The existing API could be maintained as a thin layer on top of the leaner API.

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