Database Migration Patterns

---
name: database-migration-patterns
description: "Safe schema migrations alembic rollback zero downtime"
---

# Database Migration Patterns

## Alembic
```bash
pip install alembic
alembic init migrations
alembic revision --autogenerate -m "add users table"
alembic upgrade head
```

## Rollback
```bash
alembic downgrade -1
```

## Zero-Downtime Steps
1. Add column nullable
2. Deploy app (writes to new column)
3. Backfill data
4. Add NOT NULL constraint
5. Deploy app (reads from new column)
6. Drop old column