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courses:mapreduce-tutorial:step-8 [2012/01/30 00:38] straka Improving package names of Perl programs. |
courses:mapreduce-tutorial:step-8 [2012/01/31 15:55] (current) straka |
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To use multiple reducers, the MR job must be executed by a cluster (even with one computer), not locally. The number of reducers is specified by '' | To use multiple reducers, the MR job must be executed by a cluster (even with one computer), not locally. The number of reducers is specified by '' | ||
- | perl script.pl | + | perl script.pl [-jt cluster_master | -c cluster_size [-w sec_to_wait]] [-r number_of_reducers] |
Optimal number of reducers is the same as the number of machines in the cluster, so that all the reducers can run in parallel at the same time. | Optimal number of reducers is the same as the number of machines in the cluster, so that all the reducers can run in parallel at the same time. | ||
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===== The order of keys during reduce ===== | ===== The order of keys during reduce ===== | ||
- | It is guaranteed that every reducer processes the keys in //ascending order//. | + | It is guaranteed that every reducer processes the keys in // |
On the other hand, the order of values belonging to one key is undefined. | On the other hand, the order of values belonging to one key is undefined. | ||
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# NOW EDIT THE FILE | # NOW EDIT THE FILE | ||
# $EDITOR step-8-exercise.pl | # $EDITOR step-8-exercise.pl | ||
- | rm -rf step-8-out-ex; | + | rm -rf step-8-out-ex; |
less step-8-out-ex/ | less step-8-out-ex/ | ||
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# NOW VIEW THE FILE | # NOW VIEW THE FILE | ||
# $EDITOR step-8-solution.pl | # $EDITOR step-8-solution.pl | ||
- | rm -rf step-8-out-sol; | + | rm -rf step-8-out-sol; |
less step-8-out-sol/ | less step-8-out-sol/ | ||