Cache Control
HTTP defines three basic mechanisms for controlling caches: freshness, validation, and invalidation.
- Freshness allows a response to be used without re-checking it on the origin server, and can be controlled by both the server and the client. For example, the Expires response header gives a date when the document becomes stale, and the Cache-Control: max-age directive tells the cache how many seconds the response is fresh for.
- Validation can be used to check whether a cached response is still good after it becomes stale. For example, if the response has a Last-Modified header, a cache can make a conditional request using the If-Modified-Since header to see if it has changed. The ETag (entity tag) mechanism also allows for both strong and weak validation.
- Invalidation is usually a side effect of another request that passes through the cache. For example, if a URL associated with a cached response subsequently gets a POST, PUT or DELETE request, the cached response will be invalidated.
Read more about this topic: Web Cache
Famous quotes containing the word control:
“The human mind is indeed a cave swarming with strange forms of life, most of them unconscious and unilluminated. Unless we can understand something as to how the motives that issue from this obscurity are generated, we can hardly hope to foresee or control them.”
—Charles Horton Cooley (18641929)
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