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courses:mapreduce-tutorial:step-4 [2012/01/24 21:33] straka |
courses:mapreduce-tutorial:step-4 [2012/01/25 21:52] straka |
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| ====== MapReduce Tutorial : Counters ====== | ====== MapReduce Tutorial : Counters ====== | ||
| - | Sometimes it is useful to count events differently than outputting them (key, value) pairs. For that reason Hadoop offers simple counter framework. | + | Sometimes it is useful to count events differently than outputting them as (key, value) pairs. For that reason Hadoop offers simple counter framework. |
| Hadoop maintains a collection of pre-defined and user-defined counters. Every counter is identified by its group name and counter name. To increment a counter, the following code can be used: | Hadoop maintains a collection of pre-defined and user-defined counters. Every counter is identified by its group name and counter name. To increment a counter, the following code can be used: | ||
| Line 8: | Line 8: | ||
| sub map { | sub map { | ||
| my ($self, $key, $value, $context) = @_; | my ($self, $key, $value, $context) = @_; | ||
| - | + | ||
| $context-> | $context-> | ||
| } | } | ||
| </ | </ | ||
| - | At the end of computation, | + | At the end of computation, |
| ===== Exercise ===== | ===== Exercise ===== | ||
| - | Run a MR job on / | + | Run a Hadoop |
| {{.: | {{.: | ||