CodeSignal Technical Assessment System Design and Architecture 2

Question 1

A payment service must guarantee that a transaction is processed exactly once even if retries occur. Which pattern best addresses this?

Accepted Answer

Idempotency keys stored server-side

Answer

Optimistic locking with version fields

Answer

Two-phase commit across all services

Answer

Read-your-writes consistency

Question 2

You need to fan out a single event to 10,000 subscribers with low latency. Which messaging topology is most appropriate?

Accepted Answer

Pub/sub topic with push delivery

Answer

Point-to-point queue

Answer

Request-response RPC

Answer

Polling-based job queue

Question 3

Which consistency model allows reads to see stale data but guarantees eventual convergence across replicas?

Accepted Answer

Eventual consistency

Answer

Linearizability

Answer

Sequential consistency

Answer

Strict serializability

Question 4

A microservice architecture experiences cascading failures when a downstream service is slow. Which pattern prevents this?

Accepted Answer

Circuit breaker

Answer

Retry with exponential backoff only

Answer

Synchronous chaining

Answer

Database connection pooling

Question 5

You are designing a URL shortener expected to handle 10,000 writes/sec. What is the primary bottleneck to address first?

Accepted Answer

Unique ID generation at scale

Answer

Application server CPU

Answer

DNS resolution latency

Answer

TLS handshake overhead

Question 6

Which storage engine characteristic makes LSM trees preferable over B-trees for write-heavy workloads?

Accepted Answer

LSM trees write sequentially to memory then flush to disk

Answer

Reads are always faster with LSM trees

Answer

LSM trees require no compaction

Answer

LSM trees store data in sorted order on first write

Question 7

A CDN serves static assets globally. A user in Tokyo requests an asset cached in Singapore. What metric describes the extra delay from that geographic distance?

Accepted Answer

Network latency (propagation delay)

Answer

Throughput degradation

Answer

Cache miss penalty

Answer

Bandwidth throttling