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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-326) The lowest level map-reduce APIs should be byte oriented
Date Tue, 16 Feb 2010 17:23:28 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-326?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12834319#action_12834319

Doug Cutting commented on MAPREDUCE-326:

> to avoid that, you need to invert the control

This seems very similar to what I suggested yesterday.  Is there a notable difference?

> Why should we introduce a new level of abstraction that our users absolutely don't need?

Many folks do seem to have expressed interest in this approach.  For example, Joydeep, Jay,
Eric, Chris Dyer above.  This API would also permit the efficient addition of alternate APIs
in user-code that do not use a class to specify serialization (MAPREDUCE-1126) which several
users have also expressed interest in (Ted Dunning, Alan Gates & Scott Carey).

> Wouldn't it make more sense to just add the method to MapContext to collect raw outputs?

That would make the kernel's API fatter.  Rather the proposed direction is to, long-term,
narrow the kernel API to be binary-only and to build more elaborate APIs atop that in user

> 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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