[infinispan-dev] Supporting notifications for entries expired while in the cache store - ISPN-694

[Paul Ferraro]

Is it essential?  No - but it would simplify things on my end.
If Infinispan can't implement expiration notifications, then I am forced
to use immortal cache entries and perform expiration myself.  To do
this, I have to store meta information about the cache entry along with
my actual cache values, which normally I would get for free via mortal
cache entries.

So, it would be nice to have.  If I have to wait for 6.0 for this,
that's ok.

On Thu, 2013-05-02 at 17:03 +0200, Galder Zamarreño wrote:
> Hi,
> 
> Re: https://issues.jboss.org/browse/ISPN-694
> 
> We've got a little problem here. Paul requires that entries that might
> have been expired while in the cache store, when loaded, we send
> expiration notifications for them.
> 
> The problem is that expiration checking is currently done in the
> actual cache store implementations, which makes supporting this (even
> outside the purgeExpired business) specific to each cache store. Not
> ideal.
> 
> The alternative would be for CacheLoaderInterceptor to load, do the
> checks and then remove the entries accordingly. The big problem here
> is that you're imposing a way to deal with expiration handling for all
> cache store implementations, and some might be able to do these checks
> and removals in a more efficient way if they were left to do it
> themselves. For example, having to load all entries and then decide
> which are to expire might require a lot of work, instead of
> potentially communicating directly with the cache store (imagine a
> remote cache store…) and asking it to return all the entries filtered
> by those whose expiry has not expired. 
> 
> However, even if a cache store can do that, it would lead to loading
> only those entries not expired, but then how do you send the
> notifications if those expired entries have been filtered out? You
> probably need multiple load methods here...
> 
> @Paul, do you really need this for your use case?
> 
> The simplest thing to do might be to go for option 1, and let each
> cache store send notifications for expired entries for the moment, and
> then in 6.0 revise not only the API for purgeExpired, but also the API
> for load/loadAll() to find a way that, if any expiry listeners are in
> place, a different method can be called on the cache store that
> signals it to return all entries: both expired and non-expired, and
> then let the CacheLoaderInterceptor send notifications from a central
> location.
> 
> Thoughts?
> 
> Cheers,
> --
> Galder Zamarreño
> galder at redhat.com
> twitter.com/galderz
> 
> Project Lead, Escalante
> http://escalante.io
> 
> Engineer, Infinispan
> http://infinispan.org
>