Database Migration

Covers the expand-contract pattern (add new column, backfill data, make required, drop old column), safe ways to add indexes with CONCURRENTLY, and how to handle renaming columns or changing types across multiple deploys. Includes decision trees for picking migration strategies and troubleshooting guides for when migrations fail halfway through. Works with Alembic, Knex, Rails migrations, and other common tools. The multi-phase approach feels slow when you're used to just altering tables, but it's how you avoid 3am rollbacks.