Limiting the total number of tasks per task tracker

[Oliver Senn]

Hi all,

I'm wondering whether it's possible to limit the number of task that 
are executed in parallel on a task tracker?

I'm using the parameters mapred.tasktracker.{map|reduce}.tasks.maximum
to limit the number of maps and reduces per task tracker but still 
one map and one reduce are scheduled on the same task tracker.

Thanks.

Oliver