All MAP Jobs(Java Custom Map Reduce Program) are assigned to one Node why?

[samir das mohapatra]

Hi All,

  I am using cdh4 with MRv1 . When I am running any hadoop mapreduce
program from  java  , all the map task is assigned to one node. It suppose
to distribute the map task among the cluster's nodes.

 Note : 1) My jobtracker web-UI is showing 500 nodes
            2) when  it is comming to reducer , then it is sponning into
                other  node  (other then map node)

Can nay one guide me why it is like so

Regards,
samir.