Store it in a DB for persistence, but push it out to application memory. If for some reason you expect your blacklist to be very large (maybe, you have a massi

Store it in a DB for persistence, but push it out to application memory. If for some reason you expect your blacklist to be very large (maybe, you have a massively popular API?), push a bloom filter of the blacklist instead of the actual list. Now, you (probably) only absorb the DB hit on blacklisted tokens.