/migration-safe

Catch dangerous migrations before they hit production.

Usage

What it checks

Locking

• ALTER TABLE ADD COLUMN with default → table rewrite on Postgres < 11
• ADD CONSTRAINT NOT NULL without NOT VALID first
• Long-running indexes without CONCURRENTLY
• ALTER COLUMN TYPE that requires full rewrite

Backward compat

• Renaming or dropping columns still referenced by old app code
• Type changes that break existing queries
• Reordering enums (Postgres allows but ORMs often don't)

Data integrity

• Missing NOT NULL defaults → rows with NULL after backfill
• Foreign key cascades that could nuke unrelated data
• Triggers that aren't transactional

Reversibility

• Missing down migration
• Down migration that loses data silently

Output

For each issue:

• Severity (will break prod / risky / inefficient / minor)
• What goes wrong (concrete: "5min downtime on tables > 1M rows")
• Safe alternative (e.g. expand-and-contract pattern)

Rules

• Adapt to the DB engine (Postgres / MySQL / SQLite — different gotchas)
• For Postgres, prefer CREATE INDEX CONCURRENTLY, SET NOT NULL ... NOT VALID + VALIDATE
• Suggest a multi-step rollout if a migration can't be safe in one shot