Re: no_cache tag..

Hi Henrik,

Interesting explanation - makes the concept of the refresh pattern
percentage quite easy to understand.

Could you also explain the difference between the minimum and maximum values
for the refresh time? When squid is making a decision about the freshness
of an object, how does it use the two values? Would not one value be enough
to determine freshness since an object is either "fresh" or "stale"?

Thanks,
Reuben

----- Original Message -----
From: "Henrik Nordstrom" <hno@hem.passagen.se>
To: "Marc-Adrian Napoli" <marcadrian@cia.com.au>
Cc: <squid-users@ircache.net>
Sent: Tuesday, February 08, 2000 4:17 AM
Subject: Re: no_cache tag..

> Marc-Adrian Napoli wrote:
>
> > Ahh, so if i have a website that is being cached - and there is a
certain
> > jpg on the site that has been changed, but anyone going through the
proxy
> > gets the old version after X amount of times attempting to refresh -
i'll
> > need to change the refresh_pattern for the jpg mime type?
>
> Or wait for one user to push that reload button (unless you are running
> a accelerator or "transparent proxy", and the user uses IE, in which
> case the reload button won't help).
>
> The algorithm is pretty simple:
>
> * Squid considers the object fresh for X% of the modification age when
> the object was first requested.
>
> So lets say an object was modified at 14:00, a user requested the object
> (not yet in cached) at 16:00, then the objects modification age was 2
> hours. The default configuration then says that an object is considered
> fresh for 20% of it's modification age which is 24 minues, so if another
> request arrives between 16:00 and 16:24 Squid will assume the object
> isn't modified. If a request arrives at 16:25 (or later) then Squid will
> first query the origin server to see if the object has been modified
> (after which this all starts over again, with the object considered
> fresh for 20% of it's modification age, which is a little bit longer
> time if the object hasn't been modified..)
>
> The percentage and upper limit is configured in refresh_pattern.
>
> --
> Henrik Nordstrom
> Squid hacker
Received on Mon Feb 07 2000 - 16:08:02 MST