This question evaluates a candidate's competency in large-scale distributed system design, covering scalability, low-latency real-time counter aggregation, consistency models, idempotency and deduplication, data partitioning and indexing, caching and hot-key mitigation, streaming and batch aggregation, multi-region replication, security, and observability. It is commonly asked to probe architectural trade-offs for a high-throughput favorites/counts service under heavy read/write skew and strict SLOs, falls under the System Design domain, and primarily tests practical application of architectural patterns with required conceptual understanding of distributed systems and operational concerns.
Design a backend service that lets users favorite/unfavorite items (e.g., posts, products) and exposes each item's favorite count in near real time. The system must support very high traffic with low latency and strong reliability. Assume clients are web/mobile, traffic is global, and items can be extremely skewed in popularity.
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