hadoop: Reducer output to another Reducer

Question

Is it possible to send output of a Reducer directly to another reducer if we want to group by the same key ( output of the first reducer )

Sometimes while chaining i observe that i am using a mapper just to read from input and copy same to output. Hence wondering idf it is possible to fed the output directly to reducer

Answer 1

Although you can chain map-reduce jobs, even mappers, together; as far as I know you can not chain reducers directly.

Internally you can chain mappers before reducer with ChainMapper and chain Mappers after reducer with ChainReducer.