LinkedHashMap<String, Operator<? extends OperatorDesc>> aliasToWork =
new LinkedHashMap<String, Operator<? extends OperatorDesc>>();
aliasToWork.put(mergeFilesDesc.getInputDir().toString(), mergeOp);
mergeWork.setAliasToWork(aliasToWork);
DriverContext driverCxt = new DriverContext();
MergeFileTask taskExec = new MergeFileTask();
taskExec.initialize(db.getConf(), null, driverCxt);
taskExec.setWork(mergeWork);
taskExec.setQueryPlan(this.getQueryPlan());
int ret = taskExec.execute(driverCxt);
return ret;
}