Cachen

Cachen, or caching, is the process of storing copies of data in a faster storage layer closer to the user to speed up subsequent requests. Serving data from the cache reduces latency and load on slower back-end resources. Caching is used across hardware and software, in networks and applications. The central challenge is maintaining data freshness: cached data may become stale if the original source changes.

Caches use eviction policies to make room for newer data, such as least recently used (LRU) or time-to-live (TTL) rules. Cache invalidation strategies include explicit invalidation on writes, TTL expiration, and validation with the origin via headers like ETag or Last-Modified in HTTP.

Caches exist in many forms. CPU caches (L1/L2/L3) store instructions and data close to the processor. The operating system maintains a page cache to speed disk I/O. Web caches (browsers, reverse proxies, content delivery networks) store web resources to serve users quickly. Application-level caches use in-memory stores such as Memcached or Redis to cache results of expensive computations or database queries. Database systems may also implement query caches or plan results.

Benefits include lower latency, higher throughput, and reduced database or disk contention. Drawbacks include the risk of serving stale data, increased memory usage, and the complexity of cache coherence in multi-layer architectures.

Design choices include cache size, eviction policy, data granularity, and consistency requirements. See also caching policies, HTTP caching, cache coherence, memoization.