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courses:mapreduce-tutorial:step-26 [2012/01/30 15:41]
majlis 		courses:mapreduce-tutorial:step-26 [2012/01/31 11:28]
straka
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 ====== MapReduce Tutorial : Counters, compression and job configuration ====== ====== MapReduce Tutorial : Counters, compression and job configuration ======
  
-===== Counters ===== 
  
-As in the Perl API, a mapper or a reducer can increment various counters by using ''context.getCounter("Group", "Name").increment(value)'': 
-<code java> 
-public void map(Text key, Text value, Context context) throws IOException, InterruptedException { 
-  ... 
-  context.getCounter("Group", "Name").increment(value); 
-  ... 
-} 
-</code> 
-The ''getCounter'' method returns a [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/mapreduce/Counter.html|Counter]] object, so if a counter is incremented frequently, the ''getCounter'' method can be called only once: 
-<code java> 
-public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { 
-  ... 
-  Counter values = context.getCounter("Reducer", "Number of values"); 
-  for (IntWritable value : values) { 
-    ... 
-    values.increment(1); 
-  } 
-} 
-</code> 
  
 ===== Compression ===== ===== Compression =====

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