DB Migration Guardian

Stop praying every time you run a migration in production. DB Migration Guardian turns your AI agent into a senior database reliability engineer that plans, reviews, and sequences schema changes so they ship with zero downtime — and always with a tested rollback path.

The Problem

Most migration bugs are not syntax errors. They are operational failures: a locking ALTER TABLE that freezes writes for 40 minutes, a NOT NULL column added before the backfill runs, a dropped column that a still-running old app version depends on, or a "quick index" that takes an exclusive lock on a 200M-row table. These never show up in code review and never appear in a local dev database. They only appear in production, at the worst possible time.

What It Does

DB Migration Guardian gives your agent a battle-tested operating procedure for every schema change:

1. Migration Risk Audit — Classifies each statement as safe, lock-sensitive, or destructive, and flags anything that can block reads or writes.
2. Zero-Downtime Sequencing — Rewrites risky single-step migrations into the safe expand / migrate / contract pattern (add nullable column, backfill in batches, add constraint, swap reads, drop old column) across multiple deploys.
3. Automatic Rollback Plan — Generates a matching down-migration and a manual recovery runbook for every change, so you are never one bad deploy away from an outage.
4. Backfill Strategy — Produces batched, resumable backfill scripts with throttling so you never lock a large table or saturate IO.
5. Pre-Flight Checklist — Estimates lock impact, row counts, and index build time before anything touches production.

Why Use This Skill

Writing the migration is the easy 20%. Making it safe is the hard 80%. This skill encodes the practices that experienced platform teams use — online schema change patterns, the expand-contract workflow, lock-aware ordering, and reversible-by-default design — into a repeatable procedure your agent follows every single time. No more 2 a.m. incident calls because of a forgotten backfill.

Supported Stacks

Databases: PostgreSQL (default), MySQL / MariaDB, SQLite. Migration tools: Prisma, Drizzle, Knex, TypeORM, Alembic, Flyway, Rails ActiveRecord, raw SQL. Environments: Works with any CI/CD pipeline and any agent that has filesystem and terminal access.

Use Cases

Ship schema changes to high-traffic production databases without downtime. Add a safety review step to every migration in CI before it can merge. Convert legacy "big bang" migrations into safe, reversible, multi-step rollouts. Onboard junior engineers with a guardrail that catches dangerous DDL automatically.

Known Limitations

Lock-time and build-time estimates are heuristics based on row counts and index type; always validate against a production-sized staging snapshot. The skill does not execute migrations against production on its own — it produces the plan, scripts, and rollback; a human approves and runs the deploy.