When I run Simple MR Job such as grep (about 200Maps & 4 Reduces) with 20 Opeteron Servers ( 2Way Dual-Core, 4GB RAM)
Only 2 maps are instatantiated on one machine and each map task takes 5~6 seconds to be done. As a result, about 50% CPU is unsed during the MR Job and the overall performance is not that good as I expected Configuration "mapred.tasktracker.tasks.maximum ==> 10", It only works when each map tasks last more than 10 seconds It seemds that Hadoop framework starts MR job with the limit of 2 maps on one machine. When running two similar MR Jobs concurrently, the number of maps on one machine is still 2 and CPU usage is about 50% and each MR Jobs takes almost 2times longer to be done. Then, How can I change the initial limit of map's count on the machine ?
