database-migrations

Zero-downtime database migrations in PostgreSQL use an expand-contract pattern: add nullable or defaulted new columns, backfill data, update app logic to read from the new column, then remove the old one. This approach separates schema changes from data migrations to ensure concurrent-safe operations.

The expand-contract pattern is a zero-downtime deployment strategy that separates schema and data migrations. You first expand by adding new nullable or defaulted columns and backfilling data, then update application logic, and finally contract by removing the old columns after the transition is complete.

Yes, this supports zero-downtime migrations across common ORMs including Prisma, Drizzle, Django, TypeORM, and golang-migrate. It provides reversible migration workflows and deployment guidance tailored to each tool's specific capabilities for schema changes and data migrations.

The best way to plan a reversible data migration in MySQL is to separate schema changes from data migrations and apply concurrent-safe operations. Using the expand-contract pattern ensures you can roll back safely by keeping old columns intact until the new structure is fully validated in production.

Separating schema and data migrations is required for production deployments because it enables concurrent-safe operations and zero-downtime rollbacks. Mixing them locks tables and blocks application logic, whereas splitting them allows you to backfill data gradually while the application continues serving traffic.

Rollback planning for database schema changes relies on the expand-contract pattern to ensure reversibility. By keeping old columns and data intact during the expand phase, you can safely contract or revert to the previous schema if the new application logic or data backfill encounters issues in production.