Database Migrations Without a Long Outage
A schema change can break running application instances during deployment. This guide gives you a small, testable way to approach the issue before changing a live system.
A practical workflow
- Make additive changes first, such as a nullable column, and deploy code that can read old and new shapes.
- Backfill data in controlled batches, then enforce a constraint only after checking existing rows.
What to check
Rehearse rollback and monitor locks; do not assume a single giant transaction is harmless on a busy table. Compare the result with the original problem and record what changed. If a measurement or test does not support the change, revisit the assumption rather than adding more complexity.
Keep the experiment small enough to reverse. Document the starting state, the change and the result so another person can repeat the process. Product menus and versions can change, so check the current documentation for your environment.
Official reference: Read the documentation.