Backend & systems·Caching and invalidation
you measure what fraction of lookups the cache actually answered and find out it is thirty percent and the cache is buying you almost nothing.
Cache hit rate
Also calledhit ratio, miss rate
The proportion of lookups served from cache rather than the origin. It is the first number to check before adding capacity, because a low hit rate usually means the key space is too wide or the TTL is shorter than the reuse interval, not that the cache is too small. A high hit rate on a cheap query is also worth nothing; weigh hits by what they saved.