I am wondering about what DB to choose for this goal.

I have a working filtering solution that uses Tokyo-Cabinet for domains 
and urls with REDIS which is really good in a sense of speed and space.

I want to extend the filtering DB and use some new features which will 
require me to use a dedicated DB for the black\white lists.

I Have tried mysql before but it takes so much space compared to 
Tokyo-Cabinet and it's an issue in my case.
The difference is about 100%(50MB vs 100MB).
So I am wondering about other DB solutions that will not use too much 
storage space will be fast and can scale if needed.

I have heard the names Cassandra mongo and some others but I never tried 
them but used Oracel, mySQL, BDB, Postgresql.

The DB search for domain is for either a prefix or a full match.

If you do have experience with any DB the uses key-value pair I will be 
happy to hear about it.

Thanks,
Eliezer