Re: squid never check against the source object

assa wrote:

> Is there any other configuration we can use to make squid 'never
> validate/check' the object when it's already in the cache until it was
> expired or Reload/Refresh button is hit from www browser ?

Squid does not validate an object if it has a known expiry time.

For objects without a known expiry time refresh patterns are used to
determine when the objects needs to be revalidated.

Examples:

1: Known expiry time
Expires: Tue, 30 Mar 1999 23:30:58 GMT
Not validated until set expiry time.

2: No known expiry time, but last modification time is known
Last-Modified: Thu, 31 Dec 1998 00:22:53 GMT
Here your refresh pattern determines how long the object is fresh. The
LMT factor is percentage of the time since the object was last modified
the object is considered fresh, at most max age.

3: No expiry related time known at all
When no expiry information is known Squid uses the min age of the
matching refresh rule.

Many servers have most HTML pages generated using server-side-includes
or ASP and thus does not provide any expiry information (matching case
3). However most images should be cached by rule 2 above even if the
HTML contents aren't. Very few sites provide an explicit expiry time.

Be careful when designing refresh patterns with a min age other than 0.
You can easily break dynamic or CGI applications not designed for
caching.

Also if you are on a low-bandwidth connection then it might be useful to
look into the reload-into-ims and override-lastmod refresh_pattern
options. reload-into-ims changes shift-reloads into forcing a
revalidation of the cache rather than requesting a complete fresh
object. override-lastmod enforces the min age even when last
modification time is close to now.

---
Henrik Nordstrom
Spare time Squid hacker