optimize the database performance in CodeIgniter

How can we optimize the database performance in CodeIgniter to handle large amounts of data and high traffic volumes? I'm running an online job board (https://www.dubaivacanciez.com) which features thousands of latest job updates in Dubai and Across UAE on daily basis and needs to be update and delete as well so how I can optimize my database for such a large web application so It can run smoothly without facing any downtime?