Database “Last Seen” without Hot Row Updates

                  class LastSeen
  def touch(member_id)
    key = "last_seen:#{member_id}"
    last = Redis.current.get(key)
    now = Time.current.to_i

    if last.nil? || (now - last.to_i) > 300
      Redis.current.set(key, now)
      Member.where(id: member_id).update_all(last_seen_at: Time.at(now))
    end
  end
end