Counters, status, and other output

At the end of every MapReducejob, we see output related to counters such as the following output:

12/02/12 06:28:51 INFO mapred.JobClient: Counters: 22
12/02/12 06:28:51 INFO mapred.JobClient:   Job Counters 
12/02/12 06:28:51 INFO mapred.JobClient:     Launched reduce tasks=1
12/02/12 06:28:51 INFO mapred.JobClient:     Launched map tasks=18
12/02/12 06:28:51 INFO mapred.JobClient:     Data-local map tasks=18
12/02/12 06:28:51 INFO mapred.JobClient:   SkippingTaskCounters
12/02/12 06:28:51 INFO mapred.JobClient:     MapProcessedRecords=61393
…

It is possible to add user-defined counters that will likewise be aggregated from all tasks and reported in this final output as well as in the MapReduce web UI.

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