How to decide number of mappers

Question

While running a mapreduce job in Hadoop, how to decide how many mappers are needed?

Answer 1

The number of mapper depends on the total size of the input. i.e. the total number of blocks of the input files.

Mapper= {(total data size)/ (input split size)}

If data size= 1 Tb and input split size= 100 MB

Then, Mapper= (1000*1000)/100= 10,000