For collecting size of your DB in Megabytes

data-size.rb

User.find_by_sql(
  %q{
    SELECT table_schema 'table', sum( data_length + index_length ) / 1024 / 1024 'size'
    FROM information_schema.TABLES GROUP BY table_schema;
  }
).each { |u| puts "#{u.table}: #{u.size} MB" }