Your question is Zero-Downtime Database Migrations. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Explain how you would handle database migrations for a high-traffic production database with zero downtime.
Discuss the migration sequence, backward compatibility, online schema changes, application deployment coordination, validation, observability, rollback, and recovery from partial failure. Treat the response as a practical production design rather than a discussion of a specific database vendor.