This class is the static Mapper class used by Pig
to execute Pig map only jobs. It gets a TargetedTuple
as input to the map function. Using the targets in it,
attaches the tuple as input to the target operators.
The map plan is then executed. The result is then collected
into the output collector provide by Hadoop which is configured
to write to the store file.
There is a reporter running in a separate thread that keeps
reporting progress to let the job tracker know that we are
alive. The sleep time for the reporter thread can be configured
per job via the "pig.reporter.sleep.time". By default it uses
a 10 sec sleep time