如何在现有网站上逐步引入和测试memcached？

I don't mean actually installing it. I currently use LAMP for development and would like to start using memcached for a high traffic site. Which types of db calls should be cached? (all?) and what is a good way to do load testing on a development server? Are there benchmarks that I should be looking at on my production site first? The site is primarily selects with very few updates/inserts. Are there any general guidelines that should be followed as far as ram usage vs traffic or is it mostly simply by trial and error?I don't mean actually installing it. I currentl