Transactional Information Systems by Gerard Wikum and Gottfied Vossen
ISBN 1558605088 The definitive book on "theory, algorithms and the practice of concurrency control and recovery".
In my opinion, a must have for all architects or software leads or master XP-ers who deal with databases. It deals both with theoretical aspects, with how database systems implement the algorithms, what options are available how they compare, as well as going at the application level to discuss what choices are available to the developer. All illustrated with very concrete examples as well as hard mathematics. It even has exercises.