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From "Abdul Qadeer (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4182) Streaming Documentation Update
Date Wed, 24 Sep 2008 00:45:51 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12633982#action_12633982
] 

Abdul Qadeer commented on HADOOP-4182:
--------------------------------------

I updated the wiki documentation of the page http://wiki.apache.org/hadoop/HadoopStreaming?action=diff
as follows.

Line 28: 

-Default Map input format: a line is a record in UTF-8
-  the key part ends at first TAB, the rest of the line is the value 


+Default Map input format: a line is a record in UTF-8. Every line must end
+  with an 'end of line' delimiter. The key part ends at first TAB, the rest
+  of the line is the value 

> Streaming Documentation Update
> ------------------------------
>
>                 Key: HADOOP-4182
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4182
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: contrib/streaming
>    Affects Versions: 0.19.0
>            Reporter: Abdul Qadeer
>            Priority: Minor
>             Fix For: 0.19.0
>
>
> When Text input data is used with streaming, every line is expected to end with a newline.
 Hadoop results are undefined if input files do not end in a newline.  (The results will depend
on how files are assigned to mappers.)
> Example:
> In streaming if
> mapper = xargs cat
> reducer = cat
> and the input is a two line, where each line is symbolic link in HDFS
> link1\n
> link2\n
> EOF
> link1 points to a file which contains
> This is line1EOF
> link2 points to a file which  contains
> This is line2EOF
> Now running a streaming job such that, there is only one split, will produce results:
> This is line1This is line2\t\n
> But if there were two splits, the result will be
> This is line1\t\n
> This is line2\t\n
> So in summary, the output depends on the factor that how many mappers were invoked. 
As a caution, it should be recorded in Streaming wiki that users always put a new line at
the end of each line to get away with such problems.

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