Automated Database Schema Migration in Continuous Delivery: Safety Guarantees, Rollback Strategies, and Zero-Downtime Patterns

Abstract

Database schema migrations remain one of the highest-risk operations in continuous delivery pipelines, frequently causing extended downtime or data corruption. This paper analyses 14 migration strategies across relational and NoSQL databases and evaluates their compatibility with zero-downtime deployment constraints. A formal safety taxonomy�covering backward compatibility, forward compatibility, and expand-contract patterns�is derived and validated against 320 real-world migration incidents collected from 19 organisations. A decision-tree tool, MigraSafe, is introduced to guide engineers in selecting appropriate strategies given schema change type, traffic profile, and database engine. Simulation results show MigraSafe-guided migrations reduce downtime events by 81% compared to unaided decision-making.