public JobConf getJc() {
    return jc;
  }
Reset the execution context for each new row. This function should be called only
once at the root of the operator tree -- ExecMapper.map().
Note: this function should be kept minimum since it is called for each input row.
ql/src/java/org/apache/hadoop/hive/ql/exec/mr/ExecMapperContext.java