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courses:mapreduce-tutorial:perl-api [2012/01/23 21:18]
straka 		courses:mapreduce-tutorial:perl-api [2012/01/25 14:32]
straka
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   * ''hadoop_prefix'' -- the prefix of Hadoop instalation. Default value is fine in UFAL cluster.   * ''hadoop_prefix'' -- the prefix of Hadoop instalation. Default value is fine in UFAL cluster.
   * ''keep_env'' -- which environment variables are preserved when running perl mappers, reducers, combiners and partitioners   * ''keep_env'' -- which environment variables are preserved when running perl mappers, reducers, combiners and partitioners
 +
 +==== Command line arguments supported by Hadoop::Runner::run() ====
  
 ===== Hadoop::Mapper ===== ===== Hadoop::Mapper =====
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 requires 'map'; requires 'map';
  
-sub setup() { 1; } +sub setup() {} 
-sub cleanup { 1;}+sub cleanup {}
 </code> </code>
   * ''sub map($self, $key, $value, $context)'' -- executed for every (key, value) input pair. The variable '$content' has following methods:   * ''sub map($self, $key, $value, $context)'' -- executed for every (key, value) input pair. The variable '$content' has following methods:
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   * ''sub setup($self, $context)'' -- executed once before any input (key, value) pairs are processed. The ''$context'' can be used to both produce (key, value) pairs and increment counters.   * ''sub setup($self, $context)'' -- executed once before any input (key, value) pairs are processed. The ''$context'' can be used to both produce (key, value) pairs and increment counters.
   * ''sub cleanup($self, $context)'' -- executed once after all input (key, value) pairs are processed. The ''$context'' can be used to both produce (key, value) pairs and increment counters.   * ''sub cleanup($self, $context)'' -- executed once after all input (key, value) pairs are processed. The ''$context'' can be used to both produce (key, value) pairs and increment counters.
 +
 +===== Hadoop::Reducer =====
 +
 +<code perl>
 +package Hadoop::Reduce;
 +use Moose::Role;
 +
 +requires 'reduce';
 +
 +sub setup() {}
 +sub cleanup {}
 +</code>
 +  * ''sub reduce($self, $key, $values, $context)'' -- executed for every ''$key''. The ''$values'' is an iterator with the following methods:
 +    * ''$values%%->%%value()'' -- returns the current value, undef if there is any.
 +    * ''$values%%->%%next()'' -- advance to next value. Returns true if there is any, false otherwise.
 +    * At the beginning there is no current value, the first value should be obtained by calling 'next'.
 +  * ''sub reduce($self, $key, $values, $context)'' -- the variable ''$content'' has following methods:
 +    * ''$content%%->%%write($key, $value)'' -- output the (''$key'', ''$value'') pair
 +    * ''$content%%->%%counter($group, $name, $increment)'' -- increases the counter ''$name'' in the group ''$group'' by ''$increment''
 +  * ''sub setup($self, $context)'' -- executed once before any input keys are processed. The ''$context'' can be used to both produce (key, value) pairs and increment counters.
 +  * ''sub cleanup($self, $context)'' -- executed once after all input keys are processed. The ''$context'' can be used to both produce (key, value) pairs and increment counters.
 +
 +===== Hadoop::Partitioner =====
 +
 +<code perl>
 +package Hadoop::Partitioner;
 +use Moose::Role;
 +
 +requires 'getPartition';
 +
 +sub setup {}
 +sub cleanup {}
 +
 +</code>
 +  * ''sub getPartition($self, $key, $value, $partitions)'' -- executed for every output (key, value) pair. It must return a number of partition in range 0..$partitions-1, where the output (key, value) pair should be placed.
 +  * ''sub setup($self)'' -- executed once before any input (key, value) pairs are processed.
 +  * ''sub cleanup($self)'' -- executed once after all input (key, value) pairs are processed. 
 +

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