How to handle Performance Optimization in Clean Architecture?

Optimize at the Adapter layer (caching, database indexing) and keep the Domain layer lean.

Because CA adds layers (Mappers, DTOs), there is a tiny overhead. To optimize, use caching in the Interface Adapter (Repository) layer. If a Use Case is slow due to 'N+1' queries, solve it by creating a specialized 'Query' adapter rather than compromising the Entity design.