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courses:mapreduce-tutorial:step-4 [2012/01/24 21:29] straka |
courses:mapreduce-tutorial:step-4 [2012/01/28 11:49] majlis Odstranen odkaz |
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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: | ||
<code perl> | <code perl> | ||
sub map { | sub map { | ||
my ($self, $key, $value, $context) = @_; | my ($self, $key, $value, $context) = @_; | ||
- | + | ||
- | $context-> | + | $context-> |
} | } | ||
</ | </ | ||
- | ===== Exercise ===== | + | At the end of computation, |
- | Run a MR job on / | + | ===== Exercise ===== |
- | {{.:step-4-solution.txt|Solution.pl}} | + | Run a Hadoop job on ''/ |