Postgres migration safety
Field guides for the changes that fail differently in production.
Five focused reviews with risky SQL, staged alternatives, operational evidence, and rollback boundaries.
Add NOT NULL without downtime
Expand, backfill, validate, enforce.
Build an index concurrently
Transaction boundaries, retries, progress.
Add a foreign key safely
NOT VALID, validation, both-table locks.
Change a column type
Prove metadata-only or expand-contract.
Rename or drop a column
Preserve rolling-deploy and rollback compatibility.