CQRS (Command Query Responsibility Segregation)
Most of this book has focussed on the reading and writing of data within a standard "three-tier architecture", with a database, database access or a business logic layer, and a UI. This has been generally mapped to the SQL Azure, RIA Services, and Silverlight. All reads and writes in this configuration are done to the "business logic database". Depending on how you scale your application, this can eventually lead to performance bottlenecks, just due to the assumption that everything is done against that single database (reads and writes). There are many ways to mitigate this, by using database sharding (federation), by incorporating more caching into the system (Azure AppFabric caching), and so on. but there are limitations to how far a traditional architecture can be scaled.
CQRS is a different style of architecture that is starting to gain popularity among the creators of high-performance web applications. Entire books and conferences...
