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courses:mapreduce-tutorial:step-25 [2012/01/31 09:53]
straka Change Java commandline syntax. |
courses:mapreduce-tutorial:step-25 [2012/01/31 15:12] (current)
majlis Fixed code for sorting execution. |
| * ''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> |
| 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 | 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-* | 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-* |
| |
| ---- | ---- |
| <table style="width:100%"> | <table style="width:100%"> |
| <tr> | <tr> |
| <td style="text-align:left; width: 33%; "></html>[[step-24|Step 24]]: Mappers, running Java Hadoop jobs.<html></td> | <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:center; width: 33%; "></html>[[.|Overview]]<html></td> |
| <td style="text-align:right; width: 33%; "></html>[[step-26|Step 26]]: Counters, compression and job configuration.<html></td> | <td style="text-align:right; width: 33%; "></html>[[step-26|Step 26]]: Compression and job configuration.<html></td> |
| </tr> | </tr> |
| </table> | </table> |
| </html> | </html> |
| |
