System Design Card 395 — Caching / Check
Concern
Caching can remove load from the hot path, but only if keys, invalidation, and staleness are acceptable. Caching short-link lookups or popular feed fragments can change capacity needs dramatically.
What Check means for this concern
In BASIC, the Check step is where you review the design for bottlenecks, failure modes, security gaps, observability, and cost. For Caching, that means the candidate should make this concern visible at the right moment instead of bolting it on at the end.
Design move
A good move is to review and stress-test before you hand the answer over. Tie the concern back to the user flow, the workload, and the dominant trade-off. That keeps the design grounded and makes it easier for the interviewer to follow why a cache, queue, replica, partition, or rate limiter is actually necessary.
Common miss
The miss is adding a cache as decoration without clarifying what is cached and how it expires. BASIC helps because the staged flow keeps this concern proportional to the prompt and connected to the rest of the architecture.
BASIC prompt
“When I reach the Check stage, how does Caching change the architecture, the trade-offs, or the review checklist?”