Schema migrations without downtime

A migration runs against a live application. Expand, migrate, contract lets you change a schema while both old and new code are running.

What this lesson covers

• Apply the expand, migrate, contract pattern
• Avoid locks that block writes on large tables
• Make every migration reversible or forward-only on purpose

This lesson sits in Operating Postgres, part of PostgreSQL for Developers. It assumes what came before it and leads directly into the next lesson in the module.