webcaching

WebCaching refers to techniques for storing copies of web resources at various points along the path between a user and a web server to serve subsequent requests more quickly. By reducing latency, bandwidth usage, and origin server load, caching improves performance and scalability. Caching is implemented at multiple levels, including web browsers, intermediary proxies, and content delivery networks.

HTTP caching relies on responses being marked as cacheable and on validators and freshness information. Key concepts include the Cache-Control directive, Expires header, Last-Modified and ETag validators, and the use of 304 Not Modified responses. A resource is considered fresh for a period defined by its headers; when stale, validators may be used to revalidate with the origin server. Public caches can store responses that are marked as cacheable, while private caches are limited to a single user.

Cache architectures include browser caches, transparent proxy caches, reverse proxies, and content delivery networks. CDNs maintain edge caches close to users to decrease latency and balance load. Cache keys can incorporate vary factors such as Vary headers, Accept-Language, Accept-Encoding, and cookies, influencing when a cached copy is reused.

Dynamic content, personalized pages, and content gated by authentication pose caching challenges. Techniques include cache busting via versioned URLs, selective invalidation, and appropriate Cache-Control policies. Sensitive data should not be cached in shared contexts; HTTPS caches and privacy concerns require careful configuration. While caching yields significant performance gains, it can lead to stale content if not properly managed.