migration

A database migration guide covers changes to the structure or data of a live database.

In plain words
What is it for?
It is for planning schema changes, production backfills, reindexing, dual writes, lock impact, and rollback steps.
Why use it?
It helps reduce deployment risks such as long locks, incomplete data changes, and difficult rollbacks.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/hautc-it/cil/migration
Any agent
npx skills add hautc-it/cil --skill migration
Clone the repo
git clone --depth 1 https://github.com/hautc-it/cil

Made for: Claude Code, Codex.

Per session 50 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,181 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00050 $0.01181
Opus 5 $0.00025 $0.00590
Sonnet 5 $0.00010 $0.00236
Haiku 4.5 $0.00005 $0.00118

Measured 2d ago against content hash 5531789c799f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

migration scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

templates/skills/migration/SKILL.md · 94 lines

How it starts

The opening of the file, as written. The whole thing — 94 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Skill: Database Migration

A migration is a deploy event, not a code change. Reason about it that way.

Project Context

Existing project

  1. Read CLAUDE.md — migration rules, DB constraints, or deploy-window requirements take priority.
  2. Identify the database and migration tool — read existing migration files to understand the naming convention, file structure, and execution mechanism already in use.
  3. Check data volume — how many rows are in the affected table? This determines whether the migration is instant or requires a maintenance window and special handling.
  4. Read existing migration patterns — how does this project handle rollbacks? Are down migrations written? Are backfills done inside the migration or via a separate script?
  5. Search memorymemory_search("migration [table] schema") — retrieve prior decisions, known lock patterns, or constraints on this table.
  6. Apply the checklist and patterns below within the project's established approach.

Greenfield project

No schema exists yet — foundational choices here are expensive to undo:

  1. Choose the migration tool — use the standard one for the platform and ORM in use. Prefer a dedicated migration tool over raw SQL files; it gives you history, ordering, and reproducibility.
  2. Establish file naming convention — timestamp prefix (YYYYMMDDHHMMSS_description) is safer than sequential numbers for teams working on parallel branches.
  3. Add audit columns from day onecreated_at, updated_at (and deleted_at if soft-delete is needed) on every table. Retrofitting these later requires locking every table.
  4. Decide rollback strategy upfront — write down migrations from day one, or explicitly document that the project uses forward-only migrations. Changing this policy later is disruptive.
  5. Set the backfill standard — batched (small chunks), idempotent (safe to re-run), throttled (leave headroom for live traffic). Write this into CLAUDE.md.
  6. Store the decision:
    memory_store("decision", "migrations: tool=[x], naming=[timestamp], rollback=[x], audit cols=created_at+updated_at", ["migration", "database", "conventions"])
    

Read the full file on GitHub · 94 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 94 lines · 50 tokens per session scan A 5531789c799f

Subscribe to this mod's changes

migration is a skill published in the GitHub repository hautc-it/cil (1 stars, last pushed 1mo ago), licensed MIT. It adds 50 tokens to every session and 1,181 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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