I'm thinking about making a Bitcoin client that deletes blocks from its blockchain database if they are say more than about 6 blocks deeper than the latest block AND all of its transactions have been spent. I figure this way I can still validate new blocks, ensure that transactions to my addresses are valid, and save lots of disk space.

Can I do this with libbitcoin, but without modifying its source? How hard would it be?

In your initial posts of this thread, you mention MySQL, but I see no trace of MySQL in the latest source I downloaded from Github, just leveldb and bdb. What's up with that?

You also mention the blockchain database as 'append only', does that apply that I can't delete from it?

Thanks for any tips!