Maybe for bank accounts that is true, but online casinos work pretty close to that example (except the floating point part) since we do not ever want to allow a

Maybe for bank accounts that is true, but online casinos work pretty close to that example (except the floating point part) since we do not ever want to allow an account balance to be negative. Allowing balances to be negative would be a regulatory violation so what most online casinos do is to first lock and update the balance (or balances since there is also bonus money) while making sure it does not go into the negatives and then log transaction amount plus after balances. So for online casinos I would not say that the balance is cached. And I imagine traditional banking also has accounts which are never allowed to go into the negatives where a similar solution is required.