Tiered Caching
Tiered caching is a CDN architecture where edge locations check a regional upper-tier cache before contacting the origin. When one edge misses, the upper tier may already hold the response from another edge, dramatically reducing requests that reach the origin server or upstream API.
Technical Architecture & Deep-Dive
Without tiering, each of hundreds of edge locations independently fetches content from the origin on a miss. With tiering, edges forward misses to a smaller set of regional caches, which consolidate requests and share cached responses.
For rate-limited third-party APIs, tiered caching prevents a global traffic burst from multiplying into hundreds of identical upstream calls, protecting quotas and improving consistency.
Key Architectural Benefits
Implement Tiered Caching at the Edge
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Frequently Asked Questions
Q:Does tiered caching add latency?
On a full miss it adds a hop to the upper tier, but far more requests are served from cache overall, which lowers average latency.
Related Architecture Concepts
Cache hit ratio is the percentage of requests served directly from a cache rather than forwarded to the origin. It is calculated as cache hits divided by total requests. A higher ratio means lower latency, less origin load, and fewer billable third-party API calls.
A Content Delivery Network (CDN) is a globally distributed network of servers that caches and serves content from locations close to users. By answering requests from a nearby point of presence instead of a distant origin, a CDN reduces latency, offloads origin traffic, and absorbs traffic spikes.
Request coalescing, also called request collapsing, is a caching technique where many simultaneous requests for the same uncached resource are combined into a single upstream request. The first request fetches from the origin while the others wait and receive the same response.