Attempt to estimate backup size

[tomjn]

SELECT
    Data_BB / POWER(1024,1) Data_KB,
    Data_BB / POWER(1024,2) Data_MB,
    Data_BB / POWER(1024,3) Data_GB
FROM (SELECT SUM(data_length) Data_BB FROM information_schema.tables
WHERE table_schema NOT IN ('information_schema','performance_schema','mysql')) A;

https://dba.stackexchange.com/questions/37159/how-can-i-determine-the-size-of-a-dump-file-prior-to-dumping

We may be able to use that query to estimate the SQL dump size, and provide an upper limit to prevent very large backups. It may take too long to run however

Related to #2225