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courses:mapreduce-tutorial:step-25 [2012/01/28 00:12]
straka 		courses:mapreduce-tutorial:step-25 [2012/01/31 15:12] (current)
majlis Fixed code for sorting execution.
Line 75: Line 75:
 } }
 </file> </file>
 +
 +  wget --no-check-certificate 'https://wiki.ufal.ms.mff.cuni.cz/_export/code/courses:mapreduce-tutorial:step-25?codeblock=0' -O 'WordCount.java'
 +  make -f /net/projects/hadoop/java/Makefile WordCount.jar
 +  rm -rf step-25-out-ex1; /net/projects/hadoop/bin/hadoop WordCount.jar -r 1 /home/straka/wiki/cs-text-small step-25-out-ex1
 +  less step-25-out-ex1/part-*
 +
  
 ==== Remarks ==== ==== Remarks ====
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   * ''Reducer<Text, IntWritable, Text, NullWritable>'' which discards the value and outputs key only.   * ''Reducer<Text, IntWritable, Text, NullWritable>'' which discards the value and outputs key only.
 The solution is a bit clumsy. If the mapper could output (key, value, partition) instead of just (key, value), we would not have to use the ''value'' as a partition number and the types would be simplified. The solution is a bit clumsy. If the mapper could output (key, value, partition) instead of just (key, value), we would not have to use the ''value'' as a partition number and the types would be simplified.
 +
 +**Remark:** If the type of keys or values which the mapper outputs //is different// than the type of keys and values the reducer outputs, then [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/mapreduce/Job.html#setMapOutputKeyClass(java.lang.Class)|job.setMapOutputKeyClass]] or [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/mapreduce/Job.html#setMapOutputValueClass(java.lang.Class)|job.setMapOutputValueClass]] must be used. If they are not used, the type of keys and values produced by the mapper is expected to be the same as from the reducer.
  
 <file java ArticlesAndWords.java> <file java ArticlesAndWords.java>
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     job.setOutputKeyClass(Text.class);     job.setOutputKeyClass(Text.class);
     job.setOutputValueClass(NullWritable.class);     job.setOutputValueClass(NullWritable.class);
 +    job.setMapOutputValueClass(IntWritable.class);
  
     job.setInputFormatClass(KeyValueTextInputFormat.class);     job.setInputFormatClass(KeyValueTextInputFormat.class);
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 } }
 </file> </file>
 +
 +  wget --no-check-certificate 'https://wiki.ufal.ms.mff.cuni.cz/_export/code/courses:mapreduce-tutorial:step-25?codeblock=3' -O 'ArticlesAndWords.java'
 +  make -f /net/projects/hadoop/java/Makefile ArticlesAndWords.jar
 +  rm -rf step-25-out-ex2; /net/projects/hadoop/bin/hadoop ArticlesAndWords.jar -c 2 -r 2 /home/straka/wiki/cs-text-small step-25-out-ex2
 +  less step-25-out-ex2/part-*
 +
 +===== Exercise =====
 +
 +Implement the [[.:step-13|sorting exercise]] in Java -- only the part with uniform keys.
 +
 +**Remark:** Values of type ''Text'' are sorted lexicographically, but values of type ''IntWritable'' are sorted according to value. Your mapper should therefore produce pairs of types (''IntWritable'', ''Text'').
 +
 +You can download the {{:courses:mapreduce-tutorial:step-25.txt|Sorting.java}} template and execute it.
 +
 +  wget --no-check-certificate 'https://wiki.ufal.ms.mff.cuni.cz/_media/courses:mapreduce-tutorial:step-25.txt' -O 'SortingUniform.java'
 +  # NOW VIEW THE FILE
 +  # $EDITOR SortingUniform.java
 +  make -f /net/projects/hadoop/java/Makefile SortingUniform.jar
 +  rm -rf step-25-out-uniform; /net/projects/hadoop/bin/hadoop SortingUniform.jar -c 2 -r 2 /net/projects/hadoop/examples/inputs/numbers-small step-25-out-uniform
 +  less step-25-out-uniform/part-*
 +
 +  wget --no-check-certificate 'https://wiki.ufal.ms.mff.cuni.cz/_media/courses:mapreduce-tutorial:step-25.txt' -O 'SortingNonuniform.java'
 +  # NOW VIEW THE FILE
 +  # $EDITOR SortingUniform.java
 +  make -f /net/projects/hadoop/java/Makefile SortingNonuniform.jar
 +  rm -rf step-25-out-nonuniform; /net/projects/hadoop/bin/hadoop SortingNonuniform.jar -c 2 -r 2 /net/projects/hadoop/examples/inputs/nonuniform-small  step-25-out-nonuniform
 +  less step-25-out-nonuniform/part-*
 +
 +----
 +
 +<html>
 +<table style="width:100%">
 +<tr>
 +<td style="text-align:left; width: 33%; "></html>[[step-24|Step 24]]: Mappers, running Java Hadoop jobs, counters.<html></td>
 +<td style="text-align:center; width: 33%; "></html>[[.|Overview]]<html></td>
 +<td style="text-align:right; width: 33%; "></html>[[step-26|Step 26]]: Compression and job configuration.<html></td>
 +</tr>
 +</table>
 +</html>
  

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