Work out cache hit ratio instantly with clear inputs, formula shown and shareable results.
Effective latency is the hit ratio weighted average of hit and miss latency, which shows why the last few percentage points of hit ratio matter so much: at 84 percent hits with a 40-fold latency gap, the misses still contribute most of the average. Origin load reduction equals the hit ratio directly, which is usually the stronger justification for the cache.
Cache effectiveness
hit ratio = hits / (hits + misses); effective latency = ratio x hit latency + (1 - ratio) x miss latency
It does improve, but the remaining misses dominate. Going from 90 to 99 percent hits cuts the miss contribution tenfold, which is often a bigger win than it appears.
Per request for latency purposes, and per key to find cache-unfriendly access patterns. A few hot keys can produce a high request hit ratio while most keys never hit.