Act as a Senior Solutions Architect. Design a microservices architecture for a global e-commerce platform expecting 100k concurrent users. Address the following: 1) Define service boundaries for User, Inventory, Order, and Payment services. 2) Select and justify communication patterns (Sync vs Async) between these services. 3) Design a strategy for handling data consistency across distributed transactions (e.g., Saga pattern). 4) Propose a caching layer strategy to reduce database load. 5) Explain how the system handles partial failures and circuit breaking. Provide a high-level diagram description and pseudocode for the Saga orchestration logic.