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Can't achieve load distribution

I have a simple MR job, and I want each Mapper to get one line from my
input file (which contains further instructions for lengthy processing).
Each line is 100 characters long, and I tell Hadoop to read only 100 bytes,


I see that this part works - it reads only one line at a time, and if I
change this parameter, it listens.

However, on a cluster only one node receives all the map tasks. Only one
map tasks is started. The others never get anything, they just wait. I've
added 100 seconds wait to the mapper - no change!

Any advice?

Thank you. Sincerely,