public static DatabaseSourceDriver getDatabaseSourceDriver(){
		 try{
			 Class.forName(prefetchDriverClassName);
			 Class.forName(writeDriverClassName);
			 return new SimpleDatabaseSourceDriver(prefetchConnectionString, writeConnectionString);
		 } catch(Exception ex){
			 logger.log(Level.SEVERE, "get database source:", ex);
		 }
		 return null;
	}