## page was renamed from squid-not-cached
## page was renamed from squid-cacheable
squid FAQ
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How come some objects do not get cached?
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To determine whether a given object may be cached, Squid takes many things into consideration.
The current algorithm (for Squid-2) goes something like this:
    * Responses with Cache-Control: Private are NOT cachable.
    * Responses with Cache-Control: No-Cache are NOT cachable.
    * Responses with Cache-Control: No-Store are NOT cachable.
    * Responses for requests with an Authorization header are cachable ONLY if the reponse includes     
    Cache-Control: Public.
    * The following HTTP status codes are cachable:
          o 200 OK
          o 203 Non-Authoritative Information
          o 300 Multiple Choices
          o 301 Moved Permanently
          o 410 Gone 

However, if Squid receives one of these responses from a neighbor cache, it will NOT be cached if ALL of the Date, Last-Modified, and Expires reply headers are missing.
This prevents such objects from bouncing back-and-forth between siblings forever.

A 302 Moved Temporarily response is cachable ONLY if the response also includes an Expires header.

The following HTTP status codes are "negatively cached" for a short amount of time (configurable):
    * 204 No Content
    * 305 Use Proxy
    * 400 Bad Request
    * 403 Forbidden
    * 404 Not Found
    * 405 Method Not Allowed
    * 414 Request-URI Too Large
    * 500 Internal Server Error
    * 501 Not Implemented
    * 502 Bad Gateway
    * 503 Service Unavailable
    * 504 Gateway Time-out