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From "Klaas Bosteels (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1722) Make streaming to handle non-utf8 byte array
Date Sat, 07 Mar 2009 10:36:56 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1722?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12679865#action_12679865
] 

Klaas Bosteels commented on HADOOP-1722:
----------------------------------------

Zhuweimin, presumably you're expecting the number of bytes reported by "wc -c" to be equal
to the number of bytes in your input files, but that's not what you should be expecting really.
Here's a quick outline of what happens when you run that command:

# Since you didn't specify an InputFormat, the TextInputFormat is used which leads to Text
values corresponding to "lines" (i.e. sequences of bytes ending with a newline character)
and LongWritable keys corresponding to the offsets of the lines in the file.
# Because you use rawbytes for the map input, Streaming will pass the keys and values to your
mapper as  ~<4 byte length><raw bytes>~ byte sequences. These byte sequences are
obtained using Writable serialization (i.e. by calling the {{write()}} method) and prepending
the length to the bytes obtained in this way.

You could probably get the behavior you're after by writing a custom [InputFormat|http://svn.apache.org/viewvc/hadoop/core/trunk/src/mapred/org/apache/hadoop/mapred/InputFormat.java?view=markup]
and [InputWriter|http://svn.apache.org/viewvc/hadoop/core/trunk/src/contrib/streaming/src/java/org/apache/hadoop/streaming/io/InputWriter.java?view=markup],
but out of the box it's not supported at the moment as far as I know. 

> Make streaming to handle non-utf8 byte array
> --------------------------------------------
>
>                 Key: HADOOP-1722
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1722
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: contrib/streaming
>            Reporter: Runping Qi
>            Assignee: Klaas Bosteels
>             Fix For: 0.21.0
>
>         Attachments: HADOOP-1722-branch-0.18.patch, HADOOP-1722-branch-0.19.patch, HADOOP-1722-v2.patch,
HADOOP-1722-v3.patch, HADOOP-1722-v4.patch, HADOOP-1722-v4.patch, HADOOP-1722-v5.patch, HADOOP-1722-v6.patch,
HADOOP-1722.patch
>
>
> Right now, the streaming framework expects the output sof the steam process (mapper or
reducer) are line 
> oriented UTF-8 text. This limit makes it impossible to use those programs whose outputs
may be non-UTF-8
>  (international encoding, or maybe even binary data). Streaming can overcome this limit
by introducing a simple
> encoding protocol. For example, it can allow the mapper/reducer to hexencode its keys/values,

> the framework decodes them in the Java side.
> This way, as long as the mapper/reducer executables follow this encoding protocol, 
> they can output arabitary bytearray and the streaming framework can handle them.

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