Re: no_cache tag..

Hi Henrik,

At Tuesday 11:16 AM 8/02/2000 +0100, Henrik Nordstrom wrote:
>Reuben Farrelly wrote:
>
> > Thanks for the explanation. The idea of the min and max age being
> > "boundaries" centred around the % figure helps understand the concept. The
> > squid.conf comments don't explain too well how the min and max are
> > essentially "boundaries" that the percentage freshness value cannot exceed.
> > I had the idea that they were independent values and not related to the
> > percent (obviously I was wrong).
>
>Now that you remind me I have to admit that I was partially wrong.

If _you_ made a mistake here then it must be very difficult for a beginner
to grasp the concepts without getting confused!

>The min age is a lot trickier. The exact meaning of it depends on what
>other options you have in the refresh_pattern.
>
>The default meaning (without any options) is to act as a default
>freshness TTL if the reply does not contain any other freshness related
>information. This is also why it breaks dynamic applications.

This sort of thing should be documented clearer in the Squid FAQ - since
it's quite important when it comes to ensuring that clients connecting to
the cache are seeing fresh pages. I'd like to see your explanations in the
FAQ since they are much clearer than the mathematical descriptions which
are currently at http://www.squid-cache.org/Doc/FAQ/FAQ-12.html#ss12.20

>Then there are two options which makes the min age even more aggressive:
>
>override-expire causes the min age to override any expiry information
>sent by the origin server. DON'T USE THIS UNLESS YOU KNOW WHAT YOU ARE
>DOING!
>
>override-lastmod causes the min age to be used as the lower limit for
>the % based LMT calculation.
>
>Squid should probably be changed to by default have the min age act as
>only the lower limit for LMT calculations, and options for using it as a
>default TTL or not override LMT.

Agreed. Splitting the options up may make it more involved to configure
(although with sensible defaults probably not much more) however if they
are easier to follow they may be set more intelligently by the cache
administrator. I'm no Squid guru nor am I an idiot, but the implementation
of refresh patterns has been harder to grasp than I think it should be,
given the importance of these values. One wonders how many people who set
up squid have even a clue as to what these refresh pattern values do or
even bother setting them up...

Keep up the good work on this mailing list too, Henrik. I am sure many
people would be quite lost without your advice and help.

Reuben

---------------------------------------------------------------
._/=11#####^####]-----] Reuben Farrelly reuben@reub.net
[___11________________] West Ryde, NSW 2114 Australia
+/O-O-O [ ] O-O-O\+ Trains. Music. Internet. Not a geek.
Received on Tue Feb 08 2000 - 06:42:44 MST