authenticated

Hi all.

I've been tasked with building a high performance, high capacity website for a client and so have been reading up on best practices. I'm getting familiar with the cache based approach for both authenticated and anon. users, APC, varnish etc - however I'm finding it difficult to find best practices regarding non-cachable requests.

-- EXAMPLE --

Suppose my website were to give away 500 free donuts to the first 500 people who correctly answer a multiple choice question. This figure would be stored in a field called "QTY" on the "freebie" content type.

Thanks for the linode VPS tutorial on how to install mercury, I'm pretty sure I'd be flailing about biting my toenails had I not found it. But before I go ahead and install and configure it, I can't seem to figure out whether mercury is what I'd be needing because most of my users will be authenticated users.

From what it sounds like, varnish+pressflow+awesomesauce=Mercury and that is best for boatloads of anonymous users. So my question is what kind of performance gain would I get if I install mercury running a site built for authenticated users?