Operations

Database Migration Plan Prompt

Ship a schema change without downtime or data loss — an expand-migrate-contract migration plan with backward compatibility, ordering, and a reversal path.

Overview

A schema change deployed naively locks tables, breaks the running version, or loses data on rollback. This prompt plans a safe migration using the expand/contract pattern: the backward-compatible expand step, the data backfill, the cutover, and the later contract — each ordered so the old and new code can both run during deploy, with a reversal path at every stage.

Why This Works

Expand/contract keeps both code versions working through the deploy
Putting drops in a later deploy makes the change reversible when it matters
Calling out locking steps prevents the migration that takes the site down

Best for

Schema changes on tables with live traffic and real data
Deploys where the migration and code ship together
Large tables where a naive ALTER would lock

Not for

Designing the schema in the first place — use a database design workflow
Tuning a slow query — use a SQL optimization prompt

Use cases

Planning a zero-downtime schema change
Sequencing a migration so old and new code coexist
De-risking a destructive column or table change

Customize This Resource

Opens this resource in the related tool with the fields pre-filled. Customize role, tone, and behavior rules — then generate your prompt.

Prompt Template

ROLE
You are planning a database migration that must deploy without downtime or data loss, while old and new code run simultaneously.

INPUT
The schema change:
[Current schema, desired schema, and the data involved]

PRODUCE A MIGRATION PLAN (expand / migrate / contract)
1. EXPAND: the additive, backward-compatible schema change that lets the OLD code keep working (new nullable columns, new tables, no drops).
2. BACKFILL: how existing data is migrated to the new shape — batched, resumable, non-locking.
3. DUAL-WRITE / CUTOVER: how the app writes during the transition and when reads switch to the new shape.
4. CONTRACT: the cleanup (drop old columns/tables) that runs only AFTER all code uses the new shape.
5. REVERSIBILITY: for each step, whether it's reversible and the reversal action; for irreversible ones, the safeguard (backup, dual-write window).
6. LOCK & PERFORMANCE: any step that could lock a large table, and how to avoid it.

RULES
- Old and new code must both work during the deploy window — no breaking step.
- Destructive steps (drops) come last, in a separate deploy.

OUTPUT
The ordered migration steps grouped expand → migrate → contract, each with its reversal/safeguard.

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