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Explain DB concurrency, debugging slowness, DDD and CQRS

RevolutSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenSoftware Engineering Fundamentals

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This question evaluates understanding of database concurrency control and isolation anomalies, backend performance investigation and diagnostic skills, and knowledge of architectural concepts DDD and CQRS, testing competencies in transaction semantics, operational troubleshooting signals, and architectural trade-offs.

Backend fundamentals: concurrency, performance investigation, and architecture terms

Answer the following backend questions:

  1. How do databases handle concurrency?
  • What mechanisms prevent lost updates and ensure isolation?
  • How do isolation levels relate to anomalies (dirty read, non-repeatable read, phantom read)?
  1. If users report the service is slower than usual, how do you investigate?
  • What signals do you check first?
  • How do you narrow down whether the bottleneck is CPU, DB, network, dependencies, or code changes?
  1. What are DDD and CQRS?
  • Define each term.
  • When would you use them, and what are common pitfalls?