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

[Mircea Markus]

On 2 May 2013, at 16:03, 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. 
agreed. moving the logic in the CacheLoaderInterceptor would make expiry inefficient for many cache stores.
> 
> 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...
Another way would be for CacheStore.purgeExpired to return a Set of keys that were expired. This is still too intrusive at this stage of 5.3 IMO.

> 
> @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.

+1. Paul do you use a custom CacheStore or you use one that's ships with Infinispan? If later then we should also update that specific store to trigger notifications.

Cheers,
-- 
Mircea Markus
Infinispan lead (www.infinispan.org)