Use mysql to expire sessions without loading the Rails environment, so we can call this task from cron without it being unnecessarily expensive.

expire_sessions.rake

usage = <<DESC
Use mysql to expire sessions without loading the Rails environment, so we
can call this task from cron without it being unnecessarily expensive.

Takes path to Rails app and desired RAILS_ENV as arguments.
DESC

namespace :db do
  namespace :sessions do
    desc usage
    task :expire, :app_path, :rails_env do |task, args|
      conf = YAML.load_file(File.join(args.app_path, 'config', 'database.yml'))[args.rails_env.to_s]
      sh %!mysql -u#{conf['username']} -p#{conf['password']} -e 'DELETE FROM sessions WHERE DATEDIFF(NOW(),updated_at) > 14;' #{conf['database']}!
    end
  end
end