117iMapReduce
To implement persistent tasks, there should be enough available task slots. The
number of available map/reduce task slots is the number of map/reduce tasks that
the framework can accommodate (allows to be executed) simultaneously. In Hadoop
MapReduce, the master splits a job into many small map/reduce tasks, the number
of map/reduce tasks executed simultaneously cannot be larger than the number of
the available map/reduce task slots (the default number in Hadoop is 2 per slave
worker). Once a slave worker completes an assigned task, it requests another one
from the master. iMapReduce requires to guarantee that there are sufcient available
task slots for all the persistent tasks to start at the beginning. This means that the ...