Database Internals and Architecture Questions

Focuses on how database engines work internally and how internal architecture affects performance, correctness, and scalability. Key concepts include index data structures and properties such as B trees, transaction mechanisms and isolation levels and their effects on phenomena like dirty reads and phantom reads, multi version concurrency control, write ahead logging and recovery, locking strategies and concurrency control, storage layouts including row oriented and column oriented formats, partitioning and sharding strategies, query execution engines and optimization techniques, and design trade offs between different database technologies. Candidates should be able to read and reason about explain plans and map internals to observable performance characteristics and failure modes.