Test migrations on a copy of production data before running them in production. A migration that takes 2 seconds on test data might take 2 hours on production data and lock tables the entire time.
Strong answers cover: testing migrations in CI with realistic data volumes, verifying data integrity constraints, testing stored procedures with edge cases, monitoring query performance with representative data, and testing rollback procedures. Best candidates discuss the challenges of testing stateful operations and the importance of testing migrations on production-scale data.
Advanced testing skill. Database issues can cause the most impactful production incidents. Candidates who test database operations thoroughly prevent a category of high-severity outages.