use realms to access different mysql tables

Hi Freeradius-Mailing-List, does anyone of you differentiate sql database table with realms? E.g.: Auth-Requests for user1@realm1 will be checked against table db_radius1 Auth-Requests for user1@realm2 will be checked against table db_radius2 .....and so on. I already found out that it is possible to use multiple sql instances, but for what i understand is that they would be asked/checked one after another. That would be nice for failover scenarios but if there are about 20-30 realms to check it would be result in a very slow performance (depending on mysql host speed). So is there a better way to solve this Problem? All users in one database is at the time unfortunately no option... Thanks in advance Alex