Show depth somewhere
After the overview, a strong candidate zooms into one or two of the hardest parts. The deep dive proves you can reason past a diagram. The interviewer wants to see how you handle the part that does not trivially scale.
Finding the bottleneck
- The hot path that every request touches.
- The biggest fan out where one action triggers many.
- The tightest constraint in latency, storage, or consistency.
- The part the interviewer nudges you toward.
Going deep
- Name the constraint clearly, such as write amplification.
- Propose a mechanism like sharding, a queue, or a cache.
- Quantify it with your earlier estimates.
- State the tradeoff the mechanism introduces.
Manage the focus
Do not try to deep dive everything. Choose where depth earns the most credit, usually the component that would fail first under your estimated load. Let the interviewer steer if they have a preference.
Key idea
Pick the component that breaks first under load and dive into a concrete mechanism with its tradeoffs, proving you can reason beyond the boxes.