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