Rails 2.1 will be adopted over the length of INTEGER fields to select the appropriate type of

The following code will create a bigint type of field

t.integer :foo, :limit => 8
t.column :foo2, :integer, :limit => 8


Limit are required attention should be between 5 to 8, but not too much. If you want to bigint, then the direct use: limit => 8

This way the benefits are having to go directly Writing bigint (bound to mysql) a

References:
http://dizzy.co.uk/ruby_on_rails/cheatsheets/rails-migrations