Continuous Deployment and Schema Evolution in SQL Databases

Continuous Deployment is an important enabler of rapid delivery of business value and early end user feedback. While frequent code deployment is well understood, the impact of frequent change on persistent data is less understood and supported. SQL schema evolutions in particular can make it expensive to deploy a new version, and may even lead to downtime if schema changes can only be applied by blocking operations. In this paper we study the problem of continuous deployment in the presence of database schema evolution in more detail. We identify a number of shortcomings to existing solutions and tools, mostly related to avoidable downtime and support for foreign keys. We propose a novel approach to address these problems, and provide an open source implementation. Initial evaluation suggests the approach is effective and sufficiently efficient.