java - How to access Hadoop counters values via API? -

in hadoop can increment counter in map/reduce task, looks this:

... context.getcounter(mycountersenum.somecounter).increment(1); ... 

than can find value in log.

how access them code after job completes?

what hadoop api read counter value?

counters represent global counters, defined either map-reduce framework or applications.

each counter can of enum type. can define counter enum in driver class

static enum updatecount{   cnt  } 

and increment counter in map/reduce task

public class cntreducer extends reducer<intwritable, text, intwritable, text>{  public void reduce(intwritable key,iterable<text> values,context context)  {       //do       context.getcounter(updatecount.cnt).increment(1);  } } 

and access them in driver class

public int run(string[] args) throws exception {  .  .  .  job.setinputformatclass(textinputformat.class);  job.setoutputformatclass(textoutputformat.class);  fileinputformat.setinputpaths(job,in );  fileoutputformat.setoutputpath(job, out);  job.waitforcompletion(true);  c = job.getcounters().findcounter(updatecount.cnt).getvalue();  //print "c"  } } 

c gives counter value.

you can find example here