Self-adjusting Tiered Caching System for CDN Traffic Optimization
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Solution Overview
Problem
Content delivery networks face a challenge in optimizing end user performance and origin traffic offload due to the tension between implementing the Stale-While-Revalidate (SWR) HTTP Cache-Control extension, which enhances performance but reduces origin traffic offload.
Innovation Solution
A self-adjusting tiered caching system is implemented, where the SWR is automatically set based on request rates at edge servers and set to 0 at gateway servers, using a heuristic to dynamically compute the SWR percentage as a function of the request rate, optimizing both performance and origin traffic offload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If SWR is implemented at edge servers to enhance end user performance, then response time is improved, but origin traffic offload is reduced
Solution Approach 1:
The system segments the SWR implementation across different cache tiers: edge servers use SWR with dynamically computed percentages to serve users quickly, while parent servers use SWR with 0% to maximize origin offload. This segmentation allows each tier to optimize for its specific function without compromising the other goal.
Solution Approach 2:
The edge server SWR percentage is made dynamic rather than static, computed on-the-fly based on the current request rate. When request rate is high, SWR percentage increases to improve response time; when request rate is low, SWR percentage decreases to improve origin offload. This dynamic adjustment resolves the contradiction by adapting to real-time conditions.
2Loss of time
If SWR percentage is increased at edge servers to improve response time, then end user performance is enhanced, but CDN internal traffic increases
Solution Approach 1:
The SWR percentage at edge servers is dynamically computed based on request rate using the formula: SWR percentage = 100 / (TTL × request rate). This dynamic computation ensures that SWR is only increased when request rate is high enough to justify the additional internal traffic, automatically balancing response time improvement against CDN internal traffic costs.
Solution Approach 2:
The system changes the SWR percentage parameter based on the request rate parameter. By making SWR a function of request rate rather than a fixed value, the system automatically adjusts the balance between response time and internal traffic based on actual workload conditions.
Data Source
AI summary
A tiered caching system (e.g., in an overlay network such as CDN) wherein SWR at an edge server therein is automatically set (preferably based on request rate), while SWR at a parent server therein has its SWR set at or near 0. Collectively, these SWR settings provide for a self-adjusting tiered caching system that optimizes both end user performance and the origin traffic offload.