database-migrations

Topics in the source

• Database Migration Patterns
• When to Activate
• Core Principles
• Migration Safety Checklist
• PostgreSQL Patterns
• Adding a Column Safely
• Adding an Index Without Downtime
• Renaming a Column (Zero-Downtime)

Safe, reversible database schema changes for production systems. Creating or altering database tables Adding/removing columns or indexes Running data migrations (backfill, transform) Planning zero-downtime schema changes Setting up migration tooling for a new project 1. Every change is a migration — never alter production databases manually 2. Migrations are forward-only in production — rollbacks use new forward migrations 3. Schema and data migrations are separate — never mix DDL and DML in one migration 4. Test migrations against production-sized data — a migration that works on 100 rows may lock on 10M 5. Migrations are immutable once deployed — never edit a migration that has run in production Before applying any migration: [ ] Migration has both UP and DOWN (or is explicitly marked irreversible) [ ] No full table locks on large tables (use concurrent operations) [ ] New columns have defaults or are nullable (never add NOT NULL without default) [ ] Indexes created concurrently (not inline with CREATE TABLE for existing tables) [ ] Data backfill is a separate migration from schema change [ ] Tested against a copy of production data [ ] Rollback plan documented Never rename direc

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