[squid-users] not caching

[Amos Jeffries]

On 17/03/2016 12:07 a.m., joe wrote:
> that another video same site same refresh that cached 
> 
> HTTP/1.1 200 OK
> Cache-Control: public    <--------------------notice  one cache controle
> public the other have  double public, public
> Content-Length: 18902993
> Content-Type: video/x-flv
> Expires: Sat, 21 May 2016 17:17:15 GMT
> Last-Modified: Sun, 22 Nov 2015 20:53:46 GMT
> Accept-Ranges: bytes
> Server: nginx
> Date: Wed, 16 Mar 2016 11:27:23 GMT
> Age: 313
> X-Cache: HIT from proxy.net
> Connection: keep-alive
> 

Your confusion over HIT vs MISS is probably because you are only looking
at one tiny piece of the situation.


Being cacheable is one property. This property is determined by:
 - request method
 - request Cache-Control header
 - reply status
 - reply Cache-Control, Date, Expires, Last-Modified, Age, ETag and Vary
headers
 - all request headers listed in the reply Vary header (if any)
 - refresh_pattern configuration


Being able to be stored is a second property. This property is
determined by:
 - cache_mem configuration
 - cache_dir configuration
 - refresh_pattern configuration
 - max_stale configuration settings


Being already stored is a third property. This is determined by:
 - the union of the above two properties
 - the order and cacheability of all traffic previously passed through
the proxy
 - the cache replacement algorithms


A response HIT has to be all three of those at once:
 - cacheable, and
 - able to be stored, and
 - currently already stored


Amos