java - Hadoop Mapreduce: Reducer never called -


i have simple map/reduce task. mapper called , executed reducer never called.

configuration:

conf.setjobname("index builder"); conf.setspeculativeexecution(false);  fileinputformat.setinputpaths(conf, new path(args[0].tostring())); fileoutputformat.setoutputpath(conf, new path(args[1].tostring()));  conf.setinputformat(textinputformat.class); conf.setoutputformat(nulloutputformat.class);  conf.setmapperclass(indexmapper.class); conf.setreducerclass(indexreducer.class);  conf.setmapoutputkeyclass(nullwritable.class); conf.setmapoutputvalueclass(nullwritable.class); conf.setoutputvalueclass(nullwritable.class); conf.setoutputkeyclass(nullwritable.class);

mapper signature:

public class indexmapper extends mapreducebase implements   mapper<longwritable, text, nullwritable, nullwritable> {     @override    public void map(longwritable key, text val,      outputcollector<nullwritable, nullwritable> output,      reporter reporter) throws ioexception {         // map function    }  }

ٌreducer signature:

public class indexreducer extends mapreducebase implements   reducer<nullwritable, nullwritable, nullwritable, nullwritable> {     @override    public void reduce(nullwritable arg0, iterator<nullwritable> arg1,      outputcollector<nullwritable, nullwritable> arg2, reporter reporter)      throws ioexception {       // reduce code    } }

you set output format nulloutputformat mapper, doesn't produce anything. reducer never called needs data run.


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