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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3702) add support for chaining Maps in a single Map and after a Reduce [M*/RM*]
Date Tue, 05 Aug 2008 06:50:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12619803#action_12619803
] 

Enis Soztutar commented on HADOOP-3702:
---------------------------------------

# obviously, casting the DataOutputStream to OutputStream would resolve the ambiguity. All
these kind of references could be changed (if any) to first cast the reference. 
{code}
DataOutputStream dos = ...
...
conf.write((OutputStream)dos);
...
{code}
# Although the Chain classes are not exposed, it is always good practice to use the generics.
We can get rid of  @SuppressWarnings({"unchecked"}) annotations. 

# If you are confident that this does not introduce extra overhead, I'm fine with this. 


> add support for chaining Maps in a single Map and after a Reduce [M*/RM*]
> -------------------------------------------------------------------------
>
>                 Key: HADOOP-3702
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3702
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: mapred
>         Environment: all
>            Reporter: Alejandro Abdelnur
>            Assignee: Alejandro Abdelnur
>         Attachments: patch3702.txt, patch3702.txt, patch3702.txt, patch3702.txt, patch3702.txt,
patch3702.txt, patch3702.txt, patch3702.txt, patch3702.txt, patch3702.txt
>
>
> On the same input, we usually need to run multiple Maps one after the other without no
Reduce. We also have to run multiple Maps after the Reduce.
> If all pre-Reduce Maps are chained together and run as a single Map a significant amount
of Disk I/O will be avoided. 
> Similarly all post-Reduce Maps can be chained together and run in the Reduce phase after
the Reduce.

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