[Pig Wiki] Update of "LocalJobRunner" by Shravan Narayanamurthy

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The following page has been changed by Shravan Narayanamurthy:
http://wiki.apache.org/pig/LocalJobRunner

New page:
= Local Execution Mode using LocalJobRunner from Hadoop =
Currently we have an additional Local execution engine which handles the local execution mode. The physical plan for this has to be built separately and its execution should be done differently. This also introduces different operators for local and map reduce.

Instead of this, we can reuse Hadoop's LocalJobRunner to execute the same Map Reduce Physical plans locally. So we compile the logical plan into a map reduce physical plan and create the jobcontrol object corresponding to the mapred plan. We just need to write a separate launcher which will submit the job to the LocalJobRunner instead of submitting to an external Job Tracker.

== Pros ==
* Code Reuse
* No need to write and maintain
   * Different operators
   * Different logical to physical tranlators
   * Different launchers
* The current framework does not have any progress reporting. With this approach we will have it at no extra cost.

== Cons ==
* Not sure how stable LocalJobRunner is.
* Found some bugs in hadoop-15 on it which makes it practically useless for us right now.
* These have been fixed however in hadoop-16
* Not sure how this will affect Example generator