#10 Reduce expensive queries on the database

select round(sum(length(payload))/1024) from wbo where username = '{{username}}'

There are a number of expensive queries on the database, but the heaviest by far is the constant querying of the amount of data used for users: ```sql select round(sum(length(payload))/1024) from wbo where username = '{{username}}' ``` Even fully cached in memory this takes 200 ms, and a cold query can take much longer with significant disk I/O. Suggestion: Upon update-finish, perform this query and store it in the `users` table as a new column, and query that instead.