Reducer 1 question

[#1]

I  have seen  some of my jobs are using only  one reducer in the end.  Does it mean we have one output file?  Or it depends?

[#2]

Hi,

The Reducer process the output of the mapper. After processing the data, it produces a new set of output. At last HDFS stores this output data. Reducer takes a set of an intermediate key value pair produced by the mapper as the input and runs a Reducer function on each of them.

The mappers and reducers depends on the data that is processing.

You can manually set the number of reducers with below property but i think it is not recommended.

set mapred.reduce.tasks=xx;

Regards,

Chethan YM