A pragmatic implementation of e-transactions

Three-tier applications have nice properties, which make them scalable and manageable: clients are thin and servers are stateless. However, it is challenging to implement or even define end-to-end reliability for such applications. Furthermore, it is especially hard to make these applications reliable without violating their nice properties. In previous work, we identified e-transactions as a desirable and practical end-to-end reliability guarantee for three-tier applications (S. Frolund and R. Guerraoui, 1999). Essentially, an e-transaction guarantees that the server-side transactional side-effect happens exactly once, and that the client receives the result of the server-side computation. Thus, e-transactions mask server and database failures relative to the client. We present a pragmatic implementation of e-transactions that maintains the nice properties of three-tier applications in the special, but very common case of a single back-end database.