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From "Tom White (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-326) The lowest level map-reduce APIs should be byte oriented
Date Tue, 16 Feb 2010 18:31:29 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-326?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12834367#action_12834367
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Tom White commented on MAPREDUCE-326:
-------------------------------------

bq. ... which means that pipes has to copy it into the DataOutputBuffer instead of BytesWritable.
In both cases, the framework copies it out of that object into the map output collector. 

The point is that the map output collector is backed by the DataOutputBuffers that are passed
to the write method, so there is no extra copy.

At least, this was true until MAPREDUCE-64 was committed (around the time I was writing the
proposal). Now it uses a different buffer object (BlockingBuffer, which is a DataOutputStream),
so really DataOutputBuffer should be replaced by DataOutputStream in the write() method signature.


> 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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