cachehitrate

CacheHitRate is a metric that measures how often a cache can serve a requested item without retrieving it from the primary data store. It is the ratio of cache hits to total cache accesses, typically expressed as a percentage: Hit rate = hits / (hits + misses) × 100%.

Cache hit rate is used to evaluate caching effectiveness across a range of systems, including CPU memory hierarchies, web caches, content delivery networks, and database caches. A higher rate generally reduces latency and backend load, but depends on cache size, data access patterns, and policy choices.

Calculation can be performed over a monitoring window or workload trace. It should exclude warm-up if measuring steady-state behavior. Misses include cold-start misses and evictions. Some analyses separate read and write caches or distinguish local versus distributed caches.

Several factors influence hit rate: cache size, data locality, and replacement policy (for example, least recently used, least frequently used, or ARC). Workload characteristics such as temporal locality and data popularity strongly impact the achievable rate. Multi-tier caches may aim for progressively higher cumulative hit rates.

Related metrics include cache miss rate (the complement of the hit rate) and cache latency. While a high hit rate often signals efficiency, it does not capture latency variability; a cache with a high hit rate can still incur long-tail delays for misses.