Cache hit ratio
Fraction of reads served from cache.
Origin
The metric is as old as caching itself. Modern systems target 95%+ as the healthy threshold; below 80% suggests the cache key design is wrong.
Where it shows up in production
- Facebook TAO Documented in their 2013 paper as targeting >99% read hit ratio on the social graph.
- CDN PoPs A cache hit ratio reported per object size; 90%+ for static, 50–70% for highly personalised.
On Semicolony
Sources & further reading
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