Re: How can I make it faster.

squid wrote:
>
>
> Can someone be so kind to explain me if the default values for the
> refresh_patern (0 20 4320) violates any HTTP specifications?

From the HTTP spec (1.1 dr.rev 6):

13.2.2 Heuristic Expiration

   Since origin servers do not always provide explicit expiration times,
   HTTP caches typically assign heuristic expiration times, employing
   algorithms that use other header values (such as the Last-Modified
   time) to estimate a plausible expiration time. The HTTP/1.1
   specification does not provide specific algorithms, but does impose
   worst-case constraints on their results. Since heuristic expiration
   times might compromise semantic transparency, they ought to used
   cautiously, and we encourage origin servers to provide explicit
   expiration times as much as possible.

..and..
13.2.4 Expiration Calculations

   In order to decide whether a response is fresh or stale, we need to
   compare its freshness lifetime to its age. The age is calculated as
   described in section 13.2.3; this section describes how to calculate
   the freshness lifetime, and to determine if a response has expired.
   In the discussion below, the values can be represented in any form
   appropriate for arithmetic operations.

   We use the term "expires_value" to denote the value of the Expires
   header. We use the term "max_age_value" to denote an appropriate
   value of the number of seconds carried by the "max-age" directive of
   the Cache-Control header in a response (see section 14.9.3).

   The max-age directive takes priority over Expires, so if max-age is
   present in a response, the calculation is simply:

      freshness_lifetime = max_age_value

   Otherwise, if Expires is present in the response, the calculation is:

      freshness_lifetime = expires_value - date_value

   Note that neither of these calculations is vulnerable to clock skew,
   since all of the information comes from the origin server.

   If none of Expires, Cache-Control: max-age, or Cache-Control: s-
   maxage (see section 14.9.3) appears in the response, and the response
   does not include other restrictions on caching, the cache MAY compute
   a freshness lifetime using a heuristic. The cache MUST attach Warning
   113 to any response whose age is more than 24 hours if such warning
   has not already been added.

   Also, if the response does have a Last-Modified time, the heuristic
   expiration value SHOULD be no more than some fraction of the interval
   since that time. A typical setting of this fraction might be 10%.

   The calculation to determine if a response has expired is quite
   simple:

      response_is_fresh = (freshness_lifetime > current_age)
Received on Wed Mar 17 1999 - 16:43:12 MST