Lightweight Reflection for Middleware-based Database Replication

Middleware-based database replication approaches have emerged in the last few years as an alternative to traditional database replication implemented within the database kernel. A middleware approach enables third party vendors to provide high availability solutions, a growing practice nowadays in the software industry. However, middleware solutions often lack scalability and exhibit a number of consistency and performance issues. The reason is that in most cases the middleware has to handle the database as a black box, and hence, cannot take advantage of the many optimizations implemented in the database kernel. Thus, middleware solutions often reimplement key functionality but cannot achieve the same efficiency as a kernel implementation. Reflection has been proposed during the last decade as a fruitful paradigm to separate non-functional aspects from functional ones, simplifying software development and maintenance whilst fostering reuse. However, fully reflective databases are not feasible due to the high cost of reflection. Our claim is that by exposing some minimal database functionality through a lightweight reflective interface, efficient and scalable middleware database replication can be attained. In this paper we explore a wide variety of such lightweight reflective interfaces and discuss what kind of replication algorithms they enable. We also discuss implementation alternatives for some of these interfaces and evaluate their performance