I read a detailed account on Ewan's blog on how to set up Worpress to handle 10M hits a day for minimal cost. Part of the instructions are installing software you need for any Wordpress setup: Ubuntu, MySQL, PHP, and Wordpress itself. What is the meat behind the speedup trick? Well it appears to be a combination of some products to accelerate Wordpress usage.
You want to have Nginx for high performance HTTP to start with. Then you add in Varnish, which is an HTTP accelerator. Varnish puts stuff in virtual memory and uses threads to speed things up. Then you add the W3 Total Cache plugin to Wordpress. It uses compression, and as the name implies, caching to really speed things up. It claims to increase the Wordpress throughput a massive 10 times.
One fact I found interesting was the use of Blitz to measure the speed gains. Blitz simulates a lot of users downloading pages from you web site. This all seems the domain of a skilled system adminstrator working on a shoestring budget.
Mysterious Double Instance Hampering Performance - I study the existing code base. Confer with a colleague. Then I determine the optimal plan to change the functionality to load only a slice of all the dat...