aaron wrote:
>
> for example, in discussion software you have a very clear moment when you
> want to invalidate specific pages: when a message arrives. now i don't want
> squid or any other cache to even check w/ every request. i know darn well
> when the cache is no longer valid!
I've been mulling over ways to better coordinate between a cache and the
back end web server(s) so that the staleness heuristics aren't needed.
I want a way to affect the state (fresh/stale/deleted) of cached resources.
I've been considering a couple of approaches, here's one I'm fairly happy
with.
Enable the cache to accept POST requests containing commands to expire or
refresh certain items, like so:
## Let's mark a few things as STALE
expire //http_perl/index.html ## a single item
expire //http_doc/images/* ## all resources in a directory
expire //http_doc/images/** ## all resources in a directory tree
expire ** if mime-type =~ image/* ## all images in all locations
expire ** if last-modified > now-1day ## Anything too old.
## Let's modify the Expires: time for a few things (like renewing
## a library book the cache has checked out)
expire //http_perl/maps/** at 2000/07/31 11:59:59
## Let's mark a few things stale and cause an immediate flurry
## of if-modified-since requests.
refresh ** if mime-type =~ image/*
refresh //*/~** if last-modified > now-1day
## Let's mark a few things stale and cause an immediate flurry
## of plain old GET requests. Not sure why you'd want to do this,
## but hey...
reload ** if mime-type =~ image/*
reload //*/~** if last-modified > now-1day
This would allow me to have a database trigger, file upload or form
mod_perl handler (hey! this might even be on-topic :-), File::Find cron
job, cvs/perforce/... trigger, rsync script, etc. notify the cache that
it might have stale entries. In many applications it would be better
than setting Expires headers in mod_perl-land.
Wildcards would only match URIs currently in the cache. Explicit URLs
would (or atleast could) allow cache pre-loading.
Is there anything like this out there?
This is perhaps a bit off-topic for the mod_perl list, but let's say I
implement it as a perl module that cooperates with mod_cache. Certainly
pieces of it could be used from mod_perl, and perhaps existing caching
systems written for mod_perl might be able to implement it. Or something.
- Barrie
