PlanetScale deploys multiple schema changes near-atomically by treating all changes in a branch as a single deployment, ensuring that production database schema remains stable throughout the process and changes are applied almost simultaneously when all changes are ready. This approach allows for cancellable deployments with minimal impact on production, making it easier to manage complex schema changes without disrupting the system. The use of concurrency and dependency resolution techniques, such as schemadiff and Vitess, enables PlanetScale to deploy multiple changes concurrently while maintaining a valid ordering of changes. However, there are limitations to this approach, including resource constraints and potential complexity in deploying large numbers of changes simultaneously. By treating schema changes as deployments and using advanced validation and execution mechanisms, PlanetScale provides a way to manage complex schema changes with greater control and predictability.