How about a hardware solution?

Low memory footprint and no database access and fast performance sounds like a job for an SSD (solid-state disk drive).

Of course, you may not have $5000 burning a hole in your pocket, in which case, I'd go with the dbm file :)

   MeowChow                                               
                print $/='"',(`$^X\144oc $^X\146aq1`)[-2]