public class ExecMapper
ExecMapper is the generic Map class for Hive. Together with ExecReducer it is
the bridge between the map-reduce framework and the Hive operator pipeline at
execution time. It's main responsibilities are:
- Load and setup the operator pipeline from XML
- Run the pipeline by transforming key value pairs to records and forwarding them to the operators
- Stop execution when the "limit" is reached
- Catch and handle errors during execution of the operators.