Rails sessions: rake task to clear old sessions. Details: http://maxivak.com/rails-clear-old-sessions-stored-in-database/

session_rake_task

namespace :sessions do

  desc "Clear expired sessions (more than 3 days old)"
  task :cleanup => :environment do
    sql = "DELETE FROM sessions WHERE (updated_at < '#{Date.today - 3.days}')"
    ActiveRecord::Base.connection.execute(sql)
  end

end