Class: MapRedus::Counter

Inherits:
Reducer show all
Defined in:
lib/mapredus/default_classes.rb

Overview

Emits the length of the mapped value list.

The counter reducer tells how many values were emitted by the mapper. In situations where an adder could used but only has to sum up 1’s, counter will be much faster.

This works in MapRedus because all the values produced for one key is processed (reduced) by a single worker.

Constant Summary

Constants inherited from Reducer

Reducer::DEFAULT_WAIT

Class Method Summary collapse

Methods inherited from Reducer

perform, wait

Methods inherited from QueueProcess

perform, queue

Class Method Details

.reduce(value_list) {|value_list.size| ... } ⇒ Object

Yields:

  • (value_list.size) 


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# File 'lib/mapredus/default_classes.rb', line 67

def self.reduce(value_list)
  yield value_list.size
end

.reduce_perform(process, key) ⇒ Object 



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# File 'lib/mapredus/default_classes.rb', line 63

def self.reduce_perform(process, key)
  process.emit(key, FileSystem.llen(process.map_key(key)))
end