While Mercury has previously demonstrated the raw power of Varnish to radically accelerate the delivery of cached pages with Pressflow, that's only part of the battle for high performance Drupal. Cached pages need to be generated at least once, and logged in users will be bypassing Varnish when making requests. While it's nice to know you're covered for massive traffic spikes, what about baseline load?
Well, we want to answer that question too. Keep in mind that depending on your module/theme stack, your mileage may vary. A lot. Performance tuning a complex Drupal site for logged-in traffic requires sustained diligence at the application level — code profiling, slow query log review, innovative app-specific caches, etc — as well as hardware and system optimization. However, to set some baseline expectations, we used Jacob Singh's greate starter test suite and checked out a Mercury install on a 512MB Slicehost VPS. The results are quite encouraging.
I've reduced the size of the graph displays, but the full-size files are available below.
|40||0.2 - 0.5 sec|
|60||0.2 - 1 sec|
|80||0.5 - 1 sec|
In short, what we see here is that even on a relatively low-power server Mercury is able to deliver 100s of concurrent logged-in page requests with an 80% response rate of 1 second or less. More detailed results and tests will be forthcoming in the weeks ahead, but these initial numbers are a very good place to start!