System design interview — the loop, the rubric, the primitives.
Passing system design is less about knowing architectures and more about narrating tradeoffs. This pillar breaks down the 45-minute loop into talkable segments, lists the 6 primitives every L5+ candidate should command, and surfaces the ML-systems variant the industry under-teaches.
Interview guide
How the 45-minute loop is scored, what to say in minutes 0–5, 5–25, 25–40.
ML systems
Retrieval, eval harnesses, model serving, and LLM-system tradeoffs.
Primitive — cache
Read-through, write-through, write-back, invalidation, and hot-key mitigation.
Primitive — queue
At-least-once, exactly-once, dead letter, backpressure, and ordering guarantees.
Primitive — shard
Consistent hashing, resharding, hot-shard mitigation, and cross-shard queries.
Frequently asked questions
- What is a system design interview?
- A 45–60 minute whiteboard session where the candidate designs a scalable service (e.g., a URL shortener, a news feed) end-to-end. Scoring emphasizes tradeoff reasoning, not memorized diagrams.
- How do I prepare for a system design interview?
- Three layers: (1) master 6–8 primitives (cache, queue, shard, replication, consensus, rate-limit); (2) memorize two reference architectures; (3) practice talking through tradeoffs on a clock in 4–6 mocks.
- What's the difference between L5 and L6 system design?
- L5 is one service with clear requirements. L6 adds scope: multi-team coordination, consistency/availability tradeoffs at scale, and explicit estimation of capacity and cost.
- Does Alpha Code cover ML system design?
- Yes. /system-design/ml-systems covers retrieval pipelines, eval harnesses, model-serving tradeoffs, and LLM-system design — coverage most competitors treat as an upsell.
- How is Alpha Code different from SystemsExpert?
- SystemsExpert is a separate product sold on top of AlgoExpert. Alpha Code's system-design track is included in the $19/mo subscription alongside coding, behavioral, and mock interviews.
Run a system design mock.
45-minute peer session with a transcript and scoring rubric. Included in the $19/mo subscription.