[eluser]tkyy[/eluser]
i get this question when i deal with clients sometimes, they need to be mindful of scalability or something and i answer it like this: codeigniter is small, its php. its nothing more and nothing less.
in the hands of a skillful developer codeigniter will scale like a champion, and in the hands of a novice it will fall apart rather easily when you get a small amount of traffic. it is easy to do things, but knowing how to do things the right way comes with experience. try to make as much of your site static as possible and considering learning about hardware scaling as far as database and different things you can do with apache.
if i had to give you just one piece of advice though, it would be to focus on your table structure and not to write dumb db queries.
