Scaling and Continuous Availability in Database Server Clusters Through Multiversion Replication

In this paper, the authors study replication techniques for scaling and continuous operation for a dynamic content server. The focus is on supporting transparent and fast reconfiguration of its database tier in case of overload or failures. They show that the data persistence aspects can be decoupled from reconfiguration of the database CPU. A lightweight in-memory middleware tier captures the typically heavy weight read-only requests to ensure flexible database CPU scaling and fail-over. At the same time, updates are handled by an on-disk database back-end that is in charge of making them persistent.