How much would this take to store and index in a DB?
I think we need to store something like (address, txHash, vout, value) indexed by address. Would that consume too much resources?
This thread is old - since the question was asked bitcoinj got a PostgreSQL based block store that can calculated indexes over the UTXO set. By setting it up you can do address balance queries fast. There's an open pull req to add a similar store for MySQL too.