Having a play around with Hibernate 3.2.0 and the second level caching.

My question is:

How "intelligent" is this caching?

I don't mean smart caching as in it know of the majority of the cache hits, etc. I'm after something like Hibernate being able to detect changes made on the database and then update the cache accordingly.

Typical scenario would be reporting apps refering to a web services built with Hibernate for the integration service layer.

If Hibernate only just caches in the data, is there any framework out there that adds the intelligence? If failing that, how about a development guideline?

Thanks in advance.


Shah.

Shah,

The second level cache architecture in hibernate3 is simply that, a "cache." It is limited in the fact that it can only expire objects in the cache based on a timeout. Also, according to the cache documentation it CANNOT detect changes made to the database by other applications or processes.

As for adding intellegence to the cache you might consider writing your own cache plugin coupled with some auxillary support classes to add an intellegent cache to hibernate.

Take a look at the JavaDoc for org.hibernate.cache !

Hope this helps.

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Nathan

It is unclear from the original post what exacly you expect the cache to perform, and how it should be used. Does it only detect outside changes? What about addition/removal of objects?

Okay. As I've guessed from the first response that the 2nd level cache mechanism used in Hibernate just does straightforward caching. Many thanks for the response.

This means I'll have to implement the "intelligence" myself.

I just wanted the cache to be slightly intelligent to be able to monitor data changes on the database. If so, then the cached data would then be set to stale, indicating that the cache needs to be updated. I guess this can then be automated by instantiating the update process via a Thread.

Perhaps the above can be implemented, but I was wondering if Hibernate would have this *special feature*.

I'm not sure if there is an alternative library out there that perhaps does this?

Thanks for the input guys.


Shah.

In my project, I have created a small mechanism to periodically refresh my objects, ON DEMAND, that is: I only refresh specific objects that my app was instructed to refresh (such commands reach the app via some networking component). This is because changes are relatively rare in my case, so there is no point in refreshing entire object graphs...

A third mechanism is to provide user with a button to refresh the cached data on demand and direct. But this way, users would have to wait for the process to complete. So I guess updating the cache periodically helps for the user experience.

So that makes it three ideas (one being bad):

1) Periodically update specific cached objects when instructed via the app.

2) Periodically check the database for changes (i.e. timestamp check) and update the cache accordingly.

3) Provide user interface to allow users to update cache on demand (can lead to long waits :-( ).

Anyone open to other suggestions/ideas?

BTW, does hibernate allow for CRON type scheduling when using EHCACHE? I know OSCACHE has this feature built in, but just wondering if this can be configured under Hibernate and/or Spring.

Thanks for the mega quick response!


Shah.

hibernate doesn't care what the specific second level cache does as long as it obeys the Cache and CacheProvider API.

So "detection of external changes and refresh" is perfectly fine (its event the intent) to do on the actual specific cache and/or just use the Hibernate API to evict stuff from the cache.

hibernate doesn't care what the specific second level cache does as long as it obeys the Cache and CacheProvider API.

So "detection of external changes and refresh" is perfectly fine (its event the intent) to do on the actual specific cache and/or just use the Hibernate API to evict stuff from the cache.