I'm looking for a guide book for Symfony framework, specially version-2.0. I'm interested in more advanced guides, specially about how to "squeeze" the maximum performance from symfony, optimizations for medium to large scale projects where even humble (but numerous) requests matters.
Any good reference is welcome (though I prefer books).
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I think that you can study something about the complete architecture of your system and not only about Symfony2.
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Not that i know of yet. I assume when the final release is out the door and the docs are finalized they will offer the online manual as a printed book as they have done in the past with Symfony 1.4 stuff. Until then i think youre stuck with blogs, the online docs, and the API annotations.
For symfony 1.4 there is More With Symfony but it doesnt have a ton of specifics on enterprise level performance squeezing. I've found with everything symfony and Zend you kind of have to take general PHP and web app best practices and approaches and then translate them to framework specifics.
Not sure if this is exactly what you were looking for, but I hope it's helpful.
I'd say the killer feature in this context is Symfony2's excellent support for HTTP caching and ESI.
HTTP Caching
HTTP allows you to set headers which enable caching on the client side. By installing an HTTP caching reverse proxy (such as varnish) you can improve this even more, because it will cache everything for you, serving the cached response to the site visitors.
As soon as you have authenticated users you can no longer easily cache the data though.
ESI
Edge side includes are an HTTP related spec, for combining pages. It allows you to 'include' a remote web page. This allows you to divide your page up into fragments and cache them individually. This allows you to include cached parts into your otherwise uncached page.
Caching on the edge is really one of the core concepts of Symfony2, and I highly suggest you learn about it.