Database Migration Plan

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name: database-migration-plan
description: "Write a safe, zero-downtime database migration plan for a schema change. Use when asked to plan a database migration, design a zero-downtime schema change, document an expand/contract migration, produce a rollback procedure for a database change, or coordinate a database schema update with a deployment. Produces a structured migration plan covering migration objectives, backward compatibility analysis, expand/contract phase breakdown, exact SQL, rollback steps per phase, data validation queries, and a deployment runbook."
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# Database Migration Plan Skill

Produce a complete, safe database migration plan for a schema change. A migration plan is not just the SQL — it is a coordinated sequence of steps that ensures the application stays available, data stays consistent, and every step can be rolled back independently.

The expand/contract pattern is the default approach: expand the schema to support both old and new states, migrate the application, then contract to remove the old state. Never combine schema changes and data backfills in a single migration that runs during deployment.

## Required Inputs

Ask for these if not already provided:
- **Current schema state** — the DDL or description of the table(s) as they are now
- **Target schema state** — the DDL or description of what the table(s) should look like after migration
- **Migration reason** — why this change is being made (new feature, performance fix, normalization, compliance)
- **Database engine** — PostgreSQL, MySQL, SQLite, CockroachDB, etc.
- **Estimated data volume** — approximate number of rows in affected tables
- **Deployment constraints** — is any downtime allowed? What is the expected traffic level during migration? Are there multiple app instances running?
- **Rollback window** — how long after deploy can the team roll back before the migration becomes irreversible?

## Output Format

---… load the full skill through Skill Me