Always make migrations backwards-compatible. Deploy the code that works with both old and new schema first, then run the migration, then clean up the old code path.
Strong answers cover: replication strategies, automated backups with tested restores, connection pooling, migration strategies (expand-contract pattern, backwards-compatible changes), monitoring query performance, and failover procedures. Best candidates discuss the specific challenges of schema changes on large, active tables.
Advanced operational skill. Database outages are some of the most impactful incidents. Candidates who have managed production database migrations safely demonstrate mature operational thinking.