I recently had the pleasure of helping out with a WordPress blog which had gone supernova. Within hours of being linked to from several major news sites, the server couldn’t stay up for 10 minutes without something terrible happening.
Unfortunately, WordPress isn’t setup for high performance operation out of the box. Each page request is very CPU and database intensive.
Under benchmarking, we discovered that each of the customer’s HP DL385 servers could serve between 5-10 WordPress page view’s per second, depending on the page. (For the pedantic, I’m considering anything that hits PHP as a page view.) And this is AFTER I had put major effort into MySQL performance tuning. Something had to be done, 5 page views per second is just not going to cut the mustard.
In comes the WP-Super-Cache plugin to save the day. WP-Super-Cache is a plugin which seems like it should be installed with every WordPress instance by default. It writes out entire pages to static .html files, and then instructs Apache to serve up the static .html files directly (using mod_rewrite), therefore avoiding any CPU-gobbling calls to PHP or the database. But WP-Super-Cache is smart, it automatically expires cached pages when the content is updated (by the author, or via comments).
As a result, we went from 5-10 page views per second to between 500-2000 theoretical page views per second. At this point we were hitting bandwidth bottlenecks, which is where I like to be. As long as webservers can serve up enough data to fill their own pipe, you have happy system administrators (and UNhappy network administrators).