# Safe Database Migrations

> >-

- **Type:** Skill
- **Install:** `agentstack add skill-alisinadevelo-md-files-safe-database-migrations`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [AlisinaDevelo](https://agentstack.voostack.com/s/alisinadevelo)
- **Installs:** 0
- **Category:** [Databases](https://agentstack.voostack.com/c/databases)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [AlisinaDevelo](https://github.com/AlisinaDevelo)
- **Source:** https://github.com/AlisinaDevelo/md-files/tree/main/plugins/forge/skills/safe-database-migrations

## Install

```sh
agentstack add skill-alisinadevelo-md-files-safe-database-migrations
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Safe Database Migrations

A migration runs against live data with live traffic. The goals: no downtime, no data
loss, and a way back if it goes wrong. Schema changes are the highest-risk routine
operation most teams perform — treat them with care.

## The expand/contract pattern

Never make a breaking schema change in one step. Split it across deploys so old and new
code both work at every point:

1. **Expand** — add the new structure, backward-compatible. New nullable column, new
   table, new index (built concurrently). Old code ignores it.
2. **Migrate** — backfill data in **batches** (not one giant `UPDATE`), and deploy code
   that writes to both old and new (dual-write) while still reading old.
3. **Switch** — deploy code that reads from the new structure.
4. **Contract** — once nothing references the old structure, add constraints
   (NOT NULL after backfill) and drop the old column/table in a later deploy.

Each step is independently deployable and reversible.

## Avoid long locks

- Adding a NOT NULL column with a default can rewrite the whole table on some engines —
  add nullable, backfill, then set the constraint.
- Build indexes concurrently / online where the engine supports it.
- Backfill in bounded batches with a short pause; a single large transaction holds locks
  and bloats replication lag.
- Know your engine's locking semantics for each DDL operation before you run it.

## Always have a rollback

Every forward migration needs a tested `down`, or an explicit, documented reason it's
irreversible (and then: backup first). A dropped column or table is not reversible —
treat destructive steps as one-way doors and gate them behind a verified, idle period.

## Before running on production

- Test on a copy with **realistic data volume** — a migration that's instant on 100 rows
  can lock a table for minutes on 100M.
- Estimate lock duration and replication impact.
- Make data migrations idempotent and resumable so a mid-run failure can be retried.
- Separate schema changes from data changes from code deploys where possible.

## Red flags in review

A single `UPDATE` over a huge table · `ALTER TABLE` that rewrites in place under load ·
NOT NULL added before backfill · a `down` migration that loses data silently · no batch
size on a backfill · dropping a column in the same deploy that stops using it.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [AlisinaDevelo](https://github.com/AlisinaDevelo)
- **Source:** [AlisinaDevelo/md-files](https://github.com/AlisinaDevelo/md-files)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-alisinadevelo-md-files-safe-database-migrations
- Seller: https://agentstack.voostack.com/s/alisinadevelo
- Browse the marketplace: https://agentstack.voostack.com/browse

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Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.