Detect Schema Drift Between Environments
Dump the schema from staging and production and diff them so a missing index or column is caught before deploy.
Task
Apply diff <(pg_dump --schema-only staging) <(pg_dump --schema-only prod) so the schema change is safe, reversible, and does not lock the table during peak traffic.
When to use this
A migration deploys diff <(pg_dump --schema-only staging) <(pg_dump --schema-only prod) during peak hours, takes a 40-second lock, and causes a connection pool exhaustion.
Prerequisites
- A database with migration tooling configured
- A staging environment mirroring production schema
Steps
1. Configure diff <(pg_dump --schema-only staging) <(pg_dump --schema-only prod) in the project configuration file with the recommended defaults.
diff <(pg_dump --schema-only staging) <(pg_dump --schema-only prod)
Expected output: The configuration is accepted and diff <(pg_dump --schema-only staging) <(pg_dump --schema-only prod) runs without errors on the first invocation.
2. Run the check locally to verify diff <(pg_dump --schema-only staging) <(pg_dump --schema-only prod) produces the expected result before pushing.
pnpm test
Expected output: Local run matches CI behavior; no surprises after push.
3. Add the gate to the CI pipeline so diff <(pg_dump --schema-only staging) <(pg_dump --schema-only prod) blocks merge on failure.
- name: Run add schema diff drift detect
run: pnpm test
Expected output: Pull requests with failing diff <(pg_dump --schema-only staging) <(pg_dump --schema-only prod) are blocked from merging.
Troubleshooting
Problem
The check passes locally but fails in CI
Solution
Pin dependency versions and the runtime to match CI exactly; reproduce with the same Docker image or act.
Problem
Configuration is rejected with a schema error
Solution
Check the tool version matches the config schema; older versions may not support newer fields.
Limitations
- The gate only runs on events that trigger the workflow; locally pushed commits bypass it.
- Configuration drift is possible if someone edits settings outside version control.
Make migrations safe
Start by measuring the problem. Dump the schema from staging and production and diff them so a missing index or column is caught before deploy. The most common mistake is adding the gate without first confirming it catches the issue you care about. Run diff <(pg_dump –schema-only staging) <(pg_dump –schema-only prod) against the current codebase and inspect the output before wiring it into CI.
diff <(pg_dump --schema-only staging) <(pg_dump --schema-only prod)Verify and roll back
Once the gate is in place, make failures actionable. A failing diff <(pg_dump –schema-only staging) <(pg_dump –schema-only prod) should point to the exact file and line, not a generic error. Pin the tool version in the lockfile so a upstream release does not silently change behavior. Review the gate output in every pull request just like a test result.