ZERO-DOWNTIME POSTGRESQL MIGRATIONS: A PRODUCTION PLAYBOOK FOR SAFE SCHEMA CHANGES

Summary from the TLDR DevOps newsletter

Safe PostgreSQL schema changes separate expansion, backfills, traffic switches, and cleanup so old and new application versions remain compatible during deployment. Short lock timeouts, concurrent index builds, separately validated constraints, and throttled backfills limit disruption, while monitoring replica lag and data consistency determines when each phase can proceed.