PoW and the likely future implementation of pruning are the main anti-spam measures adopted by the protocol to reduce the amount of network bandwidth and disk space occupied.
However, the most effective spam measure I believe is the one represented by opening accounts with very small amounts, as this practice is totally immune to the two measures mentioned above.
Could minimum account balance (MAB) be a solution to this problem? (Always assuming that it is perceived as such)
In conjunction with the release of a new epoch version (to mantains the MAB updated with the current protocol status, as for PoW):
- a send tx for an account that doesn't exist on the blockchain yet need to have a min amount
- (consequently a new account on the blockchain can't be created if its correlated send tx amount is lower than min amount)
- an account can send a tx only if its balance - sending amount would be >= than min amount
- accounts can be "closed" (sweeped) by their owner if balance - sending amount would be 0, accounts with 0 balance are somehow pruned by default
With a MAB of 0.01 NANO the max disk space occupied by a pruned ledger would be:
block size * (133M/0.01) = 266 byte * 13.3G = 3.53 TB
Yes, we are still far away from the current unpruned and unMABbed ledger size, but hey! =)
In a future scenario, where NANO could be worth of 10 USD/EUR, in order to be able to process txs something like 0.1 USD/EUR would be "blocked" until you decide to send everything to someone else or to an exchange.
This proposal would still allow mini/micro/nano txs, just would avoid the opening of accounts with very low and (from a practical point of view to transact) useless balances.
Have a good day