Design Top-K System — Section 7: Non-Functional Requirement (NFR) Review

Goal of this section: Explicitly map non-functional requirements to architectural decisions and show how the system meets Staff/Principal-level expectations.

1. Scalability

Requirement

• Support millions of reads per second
• Support millions of events per second
• Scale independently for reads and writes

Design Choices

• Separate ingestion, computation, and serving planes
• Partition by scope_key
• Precompute and materialize Top-K lists
• Cache hot scopes aggressively

Result

• Linear horizontal scaling
• No single bottleneck on hot read paths