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Posted to common-commits@hadoop.apache.org by Apache Wiki <wi...@apache.org> on 2011/05/14 12:24:59 UTC

[Hadoop Wiki] Update of "HadoopMapReduce" by Smith Scott

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The "HadoopMapReduce" page has been changed by Smith Scott.
http://wiki.apache.org/hadoop/HadoopMapReduce?action=diff&rev1=26&rev2=27

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  When Mapper output is collected it is partitioned, which means
  that it will be written to the output specified by the
  [[http://hadoop.apache.org/core/docs/current/api/org/apache/hadoop/mapreduce/Partitioner.html|Partitioner]]. The default [[http://hadoop.apache.org/core/docs/current/api/org/apache/hadoop/mapreduce/lib/partition/HashPartitioner.html|HashPartitioner]] uses the
- hashcode function on the key's class (which means that this hashcode function must be good in order to achieve an even workload across the reduce tasks).  See [[http://svn.apache.org/viewcvs.cgi/hadoop/core/trunk/src/mapred/org/apache/hadoop/mapred/MapTask.java?view=markup|MapTask]] for details.
+ hashcode function on the key's class (which means that this hashcode function must be good in order to achieve an even workload across the reduce tasks).
+ See [[http://svn.apache.org/viewvc/hadoop/mapreduce/trunk/src/java/org/apache/hadoop/mapred/MapTask.java?view=markup|MapTask]] for details.
  
- N input files will generate M map tasks to be run and each map
+ ''N'' input files will generate ''M'' map tasks to be run and each map
  task will generate as many output files as there are reduce
  tasks configured in the system. Each output file will be
  targeted at a specific reduce task and the map output pairs from
@@ -94, +95 @@

  [[http://hadoop.apache.org/core/docs/current/api/org/apache/hadoop/mapred/JobConf.html#setOutputFormat(java.lang.Class)|JobConf.setOutputFormat]]. If !SequentialOutputFormat is used then the output key and value
  classes must also be specified.
  
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