Database Performance and Query Optimization Questions

Evaluate ability to identify and remediate database performance bottlenecks including the N plus one query problem and expensive queries. Candidates should explain how to discover problematic queries through query plan inspection and profiling, and propose remedies such as appropriate indexing, query rewriting to use set based operations or joins, request batching and eager loading, pagination strategies, caching and denormalization when appropriate, and trade offs of read replicas or sharding. Interviewers expect discussion of measurement, monitoring, and the operational costs and consistency trade offs introduced by each optimization.