>
> yes, the "broken connection" scenario is that what I want. If
> you say that it
> doesn't really fit into the caching source, what do you
> propose instead?
It does fit in the current caching source without touching the caching source I
think :-)
> Writing
> another source wrapping source for this purpose only? (Could
> be easier than to
> refactor the existing one ...)
IMO, it is quite simple to implement this in the current code, without touching
anything. I think step-by-step this needs to be done, and I can help if you want
1) you define a new source-factory in cocoon.xconf:
<component-instance
class="org.apache.cocoon.components.source.impl.CachingSourceFactory"
logger="core.source.caching" name="cached">
<parameter name="cache-role"
value="org.apache.cocoon.caching.Cache/ExpiresAware"/>
</component-instance>
if you want to prefix you source-factory for the expires cron gets different
change "cached" into "expires-aware" or something
2) A new class, ExpiresAwareCacheImpl with role
<role default-class="org.apache.cocoon.caching.impl.ExpiresAwareCacheImpl"
name="org.apache.cocoon.caching.Cache/ExpiresAware" shorthand="expires-aware"/>
3) <expires-aware logger="core.cache.expires">
<parameter name="store" value="org.apache.excalibur.store.Store"/>
<parameter name="expiresregistry"
value="org.apache.cocoon.caching.ExpiresRegistry"/>
</expires-aware>
Now, like the EvantAwareCacheImpl, your ExpiresAwareCacheImpl examines a
cachedresponse before actually storing it in the cache, and checks for expires
validities. If found, store this like the eventRegistry in a registry, based on
some multi value maps: [expiresvalue,{key1,key2,key3}] (by the way, you have
to store the uri of the source also ofcourse)
Now, there runs a cron job, checking this ExpiresRegistry, and if expired
values found, do a refetch: if refetch succesfull: clear the cached entry and
store new cached response and register new expires time.
OTH, relying havely on this mechanism might result it naste registry behavior
resulting in OOM. Therefor, I changed the event registry we use and use
WeakReferencesRegistry instead of the AbstractDoubleMapEventRegistry, but this
for obscure reasons did not work with EHCache which did not seem to honor my
WeakReferences of cachekeys when overflowing cached objects to disk (I have
tried to reproduce without cocoon, but did not succeed), and therefor, I moved
to JCSCache, which does work quite a bit better IMO, though it has an insane
complex configuration (at least, I found it complex :-) )....but, all this is
only when you have high traffic sites in combination with *many* event
validities like we have, because of the changed cachingsource impl, returning
an eventValidity instead of timestampvalidity (though, if you have OOM
bothering you with eventcache, let me know....or if somebody is interested in
the whole story, let me know. I haven't discussed it yet on this list, because
I do not have the idea others have this problem as serious as I have had (sites
having OOM every 2 days because of the eventRegistry) and because it would
imply not using the EHCache, and some more minor changes..but again, if
somebody is interested, i would be glad to share the code and my ideas, for
example about this whole StoreJanitor idea :-) )
Anyway, Reinhard, I hope you where able to follow how I would attack the
problem, and if I can help, let me know. We might want to discuss the
"registry" OOM problems in this context as well, because with the
ExpiresRegistry analogues to the EventRegistry in combination of a cache which
is configured to have a time2live and time2idle of not eternal, you might run
into similar problems
Regards Ard
>
> >> I would like to add this
> >> feature in a
> >> transparent way and provide a configuration parameter to
> >> switch it off if you
> >> _don't_ want this behaviour but I'm not sure if I duplicate
> >> something that
> >> already exists.
> >>
> >> I can think of setting the expires parameter to -1 and using a
> >> background-refresher but this seems to be overly complex for
> >> this simple task.
> >
> > The documentation says:
> >
> > * <p>The value of the expires parameter holds some
> additional semantics.
> > * Specifying <code>-1</code> will yield the cached
> response to be considered valid
> > * always. Value <code>0</code> can be used to achieve the
> exact opposite. That is to say,
> > * the cached contents will be thrown out and updated
> immediately and unconditionally.<p>
> >
> > You want to change the -1 expires behavior, into something
> that after the expires of eg 5 minutes you have a background
> fetch (and have this in a cron job or something?)
>
> no, no, I don't want to change the behaviour of -1. I tried
> to explain that I
> *could* use it together with a background fetcher to reach my
> goal but this is
> overly complex for such a simple thing.
>
> --
> Reinhard Pötz Independent Consultant, Trainer & (IT)-Coach
>
> {Software Engineering, Open Source, Web Applications, Apache Cocoon}
>
> web(log): http://www.poetz.cc
> --------------------------------------------------------------------
>
