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--- courses:mapreduce-tutorial:step-26 [2012/01/30 15:41]
majlis
+++ courses:mapreduce-tutorial:step-26 [2012/01/31 14:41] (current)
straka
@@ Line 1: / Line 1: @@
-====== MapReduce Tutorial : Counters, compression and job configuration ======
+====== MapReduce Tutorial : 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 =====
@@ Line 64: / Line 44: @@
 <td style="text-align:left; width: 33%; "></html>[[step-25|Step 25]]: Reducers, combiners and partitioners.<html></td>
 <td style="text-align:center; width: 33%; "></html>[[.|Overview]]<html></td>
-<td style="text-align:right; width: 33%; "></html>[[step-27|Step 27]]: Custom data types.<html></td>
+<td style="text-align:right; width: 33%; "></html>[[step-27|Step 27]]: Running multiple Hadoop jobs in one source file.<html></td>
 </tr>
 </table>
 </html>

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