Cache vs CDN: Distinct layers required for sub-millisecond streaming performance
This technical explanation distinguishes between database caches for reducing backend computational work and CDNs for reducing physical network latency. It serves as a foundational guide for engineers on how these two distinct caching strategies are combined to optimize streaming platform performance.
Key Takeaways
- Caches (Redis/Memcached) sit adjacent to databases to eliminate repetitive computational work and enable sub-millisecond response times for dynamic, per-user data.
- CDNs use a global network of edge servers to minimize geographical latency, serving static assets like video segments from nodes physically close to the end user.
- Cache layers do not reduce network distance; a user in Tokyo accessing a Frankfurt-based cache still incurs hundreds of milliseconds of round-trip latency.
- CDNs offload origin bandwidth but are generally ineffective for highly personalized or rapidly changing dashboard data that cannot be cached at the edge.
Why It Matters
Distinguishing between these layers is critical for infrastructure teams as streaming platforms scale globally. Relying solely on a database cache fails to solve for last-mile delivery lag, while a CDN alone cannot protect the origin from expensive, personalized database queries. As interactive streaming and real-time commerce demand tighter latency budgets, engineers must implement a hybrid approach—CDN at the edge for delivery and in-memory caches at the backend for state management. Watch for a shift toward 'edge-compute' services that attempt to merge these functions by bringing dynamic KV-stores directly into the CDN PoP.
Additional Context
The 2026 delivery landscape is increasingly defined by third-generation CDN systems that collapse the boundary between backend caching and edge delivery. According to Precedence Research, the global edge computing market is projected to reach $554 billion by 2025, driven by the need for sub-20ms latency in streaming and AI applications (per YouWare, February 2026). Providers like Cloudflare and Fastly now offer programmable edge logic and persistent key-value storage directly at the network edge, allowing some dynamic workloads to migrate out of the central origin entirely (per BlazingCDN, May 2026).
Infrastructure choices are also personalizing around specific performance trade-offs. While Redis remains the industry default for its rich data structures, multi-threaded alternatives like Memcached are seeing renewed interest for simple key-value workloads that hit single-core bottlenecks at scales exceeding 150,000 requests per second (per DevGenius, March 2026). This is particularly relevant for high-concurrency events where tail latency consistency determines viewer retention.
Furthermore, the push for profitability over raw growth has led 65% of enterprise CDN users to adopt multi-CDN strategies (per WorldMetrics, June 2026). By utilizing multiple delivery partners, platforms can optimize for regional ISP penetration and avoid the 'cold-cache stampedes' that occur when a single provider's node lacks requested content. This architectural complexity mirrors the rise of hybrid cloud models, where predictable workloads are brought back to private infrastructure while using global CDNs for burst capacity (per Broadpeak, February 2026).
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