lots of traffic mysql side

Hi, SET NAMES utf8 are always initialized on runtime to make sure your application have the correct encoding. Or you won't be able to save and retrieve your information correctly, your symbols may end up as ANSI otherwise.

Technically this can be "fixed" if you change your MySQL server settings to default into utf8 and your PHP client to be utf8 as well. Then you could hack it away from CodeIgniter, you can't turn it off.

I guess you are running a minimum of 40k visits a minute in your AB test? As you will get a minimum one SET NAMES for every visit on your website. I hope you are using a cache engine (memory and html) in case you want to handle that amount of traffic. Also, please remove the debug mode when going offline. Logging slow queries etc in MySQL will have an negative impact on your server.