System Design Card 413 — Consistency Models / Structure
Concern
Consistency choices shape correctness guarantees, latency, and user-visible behavior. A ledger, a chat app, and an analytics dashboard can tolerate different forms of staleness or reconciliation.
What Structure means for this concern
In BASIC, the Structure step is where you turn the chosen trade-offs into a clear high-level architecture and request flow. For Consistency Models, 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 make the plan visible before full execution. 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 saying 'eventual consistency' or 'strong consistency' without connecting it to the user-facing requirement. 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 Structure stage, how does Consistency Models change the architecture, the trade-offs, or the review checklist?”