what is chain reducer

Predefined Mapper and Reducer Classes

Hadoop provided some predefined Mapper and Reducer classes in its Java API and these will be helpful in writing simple or default mapreduce jobs. A few among the entire list of predefined mapper and reducer classes are provided below. Identity Mapper Identity Mapper is the default Mapper class provided by hadoop and this will be picked automatically when no mapper is specified in Mapreduce driver class. Identity Mapper class implements […]