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From Robert Evans <ev...@yahoo-inc.com>
Subject Re: Issue with Hadoop Streaming
Date Thu, 02 Aug 2012 19:59:00 GMT
It depends on the input format you use.  You probably want to look at using NLineInputFormat

From: Devi Kumarappan <kpalania@att.net<mailto:kpalania@att.net>>
Reply-To: "mapreduce-user@hadoop.apache.org<mailto:mapreduce-user@hadoop.apache.org>"
<mapreduce-user@hadoop.apache.org<mailto:mapreduce-user@hadoop.apache.org>>
Date: Wednesday, August 1, 2012 8:09 PM
To: "common-user@hadoop.apache.org<mailto:common-user@hadoop.apache.org>" <common-user@hadoop.apache.org<mailto:common-user@hadoop.apache.org>>,
"mapreduce-user@hadoop.apache.org<mailto:mapreduce-user@hadoop.apache.org>" <mapreduce-user@hadoop.apache.org<mailto:mapreduce-user@hadoop.apache.org>>
Subject: Issue with Hadoop Streaming

I am trying to run hadoop streaming using perl script as the mapper and with no reducer. My
requirement is for the Mapper  to run on one file at a time.  since I have to do pattern processing
in the entire contents of one file at a time and the file size is small.

Hadoop streaming manual suggests the following solution

 *   Generate a file containing the full HDFS path of the input files. Each map task would
get one file name as input.
 *   Create a mapper script which, given a filename, will get the file to local disk, gzip
the file and put it back in the desired output directory.

I am running the fllowing command.

hadoop jar /usr/lib/hadoop-0.20/contrib/streaming/hadoop-streaming-0.20.2-cdh3u3.jar -input
/user/devi/file.txt -output /user/devi/s_output -mapper "/usr/bin/perl /home/devi/Perl/crash_parser.pl"



/user/devi/file.txt contains the following two lines.

/user/devi/s_input/a.txt
/user/devi/s_input/b.txt

When this runs, instead of spawing two mappers for a.txt and b.txt as per the document, only
one mapper is being spawned and the perl script gets the /user/devi/s_input/a.txt and /user/devi/s_input/b.txt
as the inputs.



How could I make the mapper perl script to run using only one file at a time ?



Appreciate your help, Thanks, Devi





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