[z3t4]

When making a double entry accounting database, the users should only have INSERT and SELECT privileges to the table, so in order to correct a mistake you make another insert. There is really no scaling problem as the data is immutable. And at the end of the year you can achieve the ledger - so you don't have to map over it to check the account status - just put the sum of the last year as the first insert. A database service would still be useful though, in order to make sure you do not edit the values.