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https://issues.apache.org/jira/browse/HADOOP-4182?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Owen O'Malley resolved HADOOP-4182.
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Resolution: Won't Fix
There isn't much that streaming can do. In the first case, your application
gives the streaming framework:
line1line2EOF
In the second case you give it:
line1EOF in one map
and
line2EOF in the second map
streaming needs line based data, so the entire input is treated as a line.
Leading to the differences that you observed.
> 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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