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From "Harsh J Chouraria (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-2410) document multiple keys per reducer oddity in hadoop streaming FAQ
Date Wed, 11 May 2011 08:16:47 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-2410?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Harsh J Chouraria updated MAPREDUCE-2410:
-----------------------------------------

    Attachment: MAPREDUCE-2410.r1.diff

Dieter,

I've attached a patch that adds a documentation entry to the streaming's FAQ page.

Let me know if the following is sufficient (its what the patch contains as well):

{code}

+<section>
+<title>How does the use of streaming differ from the Java MapReduce API?</title>
+<p>
+    The Java MapReduce API provides a higher level API that lets the developer focus on writing
map and reduce functions that act upon a pair of key and associated value(s). The Java API
takes care of the iteration over the data source behind the scenes.
+    In streaming, the framework pours in the input data over the stdin to the mapper/reduce
program, and thus these programs ought to be written from the reading (via stdin) iteration
level.
+</p>
+</section>

{code}

> document multiple keys per reducer oddity in hadoop streaming FAQ
> -----------------------------------------------------------------
>
>                 Key: MAPREDUCE-2410
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2410
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: contrib/streaming, documentation
>            Reporter: Dieter Plaetinck
>            Priority: Minor
>              Labels: newbie
>         Attachments: MAPREDUCE-2410.r1.diff
>
>   Original Estimate: 40m
>  Remaining Estimate: 40m
>
> Hi,
> for a newcomer to hadoop streaming, it comes as a surprise that the reducer receives
arbitrary keys, unlike the "real" hadoop where a reducer works on a single key.
> An explanation for this is @ http://mail-archives.apache.org/mod_mbox/hadoop-common-user/201103.mbox/browser
> I suggest to add this to the FAQ of hadoop streaming

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