Optimizing Kohana-based Websites for Speed and Scalability

A site I built with Kohana was slammed with an enormous amount of traffic yesterday, causing me to take a step back and evaluate some of the design. I'm curious what are some standard techniques for optimizing Kohana-based applications?

Achievements / Badges system

I have been browsing this site for the answer but I'm still a little unsure how to plan a similar system in its database structure and implementation.

What is best choice for realtime web app development?

I have decided to make a new web app.

The web app would be high concurrency and using Socket.io. to implement streaming data in realtime.