cache empties itself?

[Michael S. Fischer]

On Thu, Apr 3, 2008 at 11:53 AM, Ricardo Newbery <ric at digitalmarbles.com> wrote:
 >  On Apr 3, 2008, at 11:04 AM, Michael S. Fischer wrote:
> > On Thu, Apr 3, 2008 at 10:58 AM, Sascha Ottolski <ottolski at web.de> wrote:
> >
> > > and I don't wan't upstream caches or browsers to cache that long, only
> > > varnish, so setting headers doesn't seem to fit.
> > >
> >
> > Why not?  Just curious.   If it's truly cachable content, it seems as
> > though it would make sense (both for your performance and your
> > bandwidth outlays) to let browsers cache.
>
>  Can't speak for the OP but a common use case is where you want an
> aggressive cache but still need to retain the ability to purge the cache
> when content changes.  As far as I know, there are only two ways to do this
> without contaminating downstream caches with potentially stale content...
> via special treatment in the varnish config (which is what the OP is trying
> to do) or using a special header that only your varnish instance will
> recognize (like Surrogate-Control, which as far as I know Varnish does not
> support out-of-the-box but Squid3 does).

Seems to me that this is rather brittle and error-prone.

- If a particular resource is truly dynamic, then it should not be
cachable at all.
- If a particular resource can be considered static (i.e. cachable),
yet updateable, then it is *far* safer to version your URLs, as you
have zero control over intermediate proxies.

--Michael