This is a good summary paper on the database internals and major architectural decisions: http://db.cs.berkeley.edu/papers/fntdb07-architecture.pdf
I've been looking for books or articles on Database Architecture and internals for a while now.
I found this paper "Architecture of a Database System"  to be an excellent starting point, it's written by database veterans James Hamilton and Micheal Stonebraker and references other much deeper works.
I've always liked Pat Shaughnessy's work, Ruby under a Microscope was a fantastic introduction to MRI 2.0. I really hope to see more works like these.
I like the VLDB papers, and papers of similar conferences. But most of upscaledb's architecture is auto-didactic.
edit: this is a good book: http://db.cs.berkeley.edu/papers/fntdb07-architecture.pdf
I hope my sales improve as soon as I learn to do marketing ;)