Re: [squid-users] Tool for calculating the object-freshness

From: Amos Jeffries <>
Date: Tue, 20 Dec 2011 22:13:55 +1300

On 20/12/2011 7:40 p.m., Tom Tux wrote:
> Hi
> I have found the following web-based tool to calculate the objects freshness:
> If it's useful for others too, can a site-admin publish this url on
> "" (perhaps 'Related Software')?
> Thanks and regards,
> Tom

Nice tool. Although if you use it I recommend also using the
tool to see problems with other details which affect caching service.

  * it displays what it calls "header contents" dates in a format which
is invalid for HTTP.
  * it omits several of the age limit directives Squid considers for the
algorithm (max_stale, and refresh_pattern max-stale=N)
  * it omits about half of the cache-control directives which Squid uses
to adjust the algorithm (max-stale, stale-if-error,
stale-while-revalidate, must-revalidate, no-cache)
  * it does not permit HTTP/1.1 server cache-control header contents to
be entered for consideration, this may drastically alter the algorithm
  * it crashes the script if you put some very common invalid header
values into the input fields.
  * it assumes ETag: and Vary: are identical on the client request, but
does not state that anywhere for the script user to be aware of the

It may have worked well for Squid-2.5 and early 2.6/3.0 responses but
newer Squid as you can see from the above, have quite a few more
protocol details and config settings involved with the calculation.

Side Note:
   we are working upstream on JavaScript extensions to the cache manager
reports. If anyone feels interest towards creating a JS script which can
take cached object headers and config details and produce a little
service-state report like that tools output please contact kinkie via
the squid-dev mailing list about it.

Received on Tue Dec 20 2011 - 09:14:03 MST

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