db-migration SKILL.md skillA

This file is byte-identical to the first copy the registry indexed, one of 8 indexed copies. Same content hash, so the same checks give both the same grade.

db-migration from globalmpc/backendskills is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.

mdr add globalmpc/backendskills/db-migration@git:20261105.6131a31

Pins git:20261105.6131a31 in mdr.lock. Pin the fingerprint instead.

Audit grade

A, 17 of 17 checks passed

Kind

SKILL.md skill

Repository

globalmpc/backendskills

Path

bench/results/2026-11-04/checkout-with-1-20261105081443-28376/skills/db-migration/SKILL.md

Versions recorded

1

Latest version

git:20261105.6131a31, committed Nov 5, 2026

Size

4,661 bytes

Repository stars

25

License

MIT

Rules for database schema changes. Use for any new table, column, index, constraint, enum or trigger, any data backfill, and any migration file.

Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.

What the file says

# Schema change

Examples are Postgres. Assume the table is large and the app is live: deploys are rolling, so the previous
version of the app keeps running against the new schema for a few minutes.

## 1. Expand, then contract: never rename or drop in the same deploy

Why: the version still running during the deploy queries the old name and fails until the deploy finishes.

```sql
-- Bad: the running version breaks the moment this migration lands
alter table customers rename column name to full_name;

-- Good, deploy 1: add the new column and fill it. Keep it in sync until every server runs the new code
-- (write both in the app, or use a trigger).
alter table customers add column full_name text;
update customers set full_name = name where full_name is null;  -- batch it on big tables (rule 4)
-- Deploy 2, once nothing reads the old column: drop name.
```

The same applies to dropping a table or column, and to narrowing a type. Adding is safe. Removing waits
for a later deploy.

## 2. Indexes on big tables are built concurrently

Why: a plain `create index` blocks every write to the table until it finishes, which can take minutes.

```sql
-- Bad
…

Read the whole file at its exact version.

How to install

mdr add globalmpc/backendskills/db-migration@sha256:2a1e42884f653478

[![mdr](https://markdownregistry.com/badge/art_hd6mzk7zmzzfg4ah.svg)](https://markdownregistry.com/a/art_hd6mzk7zmzzfg4ah)

Versions

The registry has recorded 1 version of this file, committed on Nov 5, 2026.

Audit of the latest version

Source

API

GET https://markdownregistry.com/api/v1/artifacts/art_hd6mzk7zmzzfg4ah
GET https://markdownregistry.com/api/v1/resolve?ref=globalmpc/backendskills/db-migration
GET https://markdownregistry.com/api/v1/blob/2a1e42884f6534788822c2ceff9275641b85a4003e235f69e86fd07649eff7e9

Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.

Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.

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