#System Design

Discuss the thought process behind designing a service for spatial queries. Address concepts such as geospatial indexing, caching, Haversine distance, and scaling for millions of users.

Design a service to identify the n closest restaurants to a user in real time. Explain the system architecture, including geospatial indexing, caching strategies, and considerations for scaling to millions of users.

Design an AdClick Aggregator Service with a focus on multiple design approaches, including Lambda vs Kappa architecture, database schema design, entity relationships, indexing, and the choice between SQL and NoSQL databases. Justify your choices with real use cases and address concerns around scaling, fault tolerance, and observability.

Design a high-level architecture for a Unique ID Generator, discussing its components and potential challenges.

Discuss how to ensure the correctness of a system operating in a concurrent environment, detailing concurrency issues and solutions.