Top Essentials Cache and Multiple Application Servers

Hello,
I'm developing a new servlets/services application in Java using tomcat and playing around with toplink essentials. Is it possible, when using multiple servers, to expire cached objects? Eg I update user account info on server 1, but 2 and 3 still have old data. The documentation and blogs I have read seem to indicate you either have to force a refresh of the object or set up readAllQueries to go direct to the db (which rather defeats the purpose of having a cache?) - for fresh data. Though I agree there are some places where up to the moment data is not always required, building a system to scale with expiry caching across multiple app servers seems like something toplink essentials SHOULD be able to do.
Also, is there any work on when the new rev of Toplink Essentials would be out? I see posts about the 11G preview but that's regular toplink.
Thanks in advance!

There are several caching options in TopLink Essentials to handle stale data.

Some of the settings are available through properties in the persistence.xml, but for most you will need to use a DescriptorCustomizer or SessionCustomizer and use the API of ClassDescriptor (refer to JavaDocs for additional info).

Caching options include:
- Cache Type : (weak, hard, soft, none), a weak cache will decrease stale data.
- Isolated (shared) : You can set the descriptor to be isolated or cache not shared to avoid caching the class.
- Refresh : You can enable refreshing at the class or query level.

A ClassDescriptor does have an invalidation policy, but the policies for invalidating based on a time-to-live or time-of-day were not ported from TopLink to TopLink Essentials, however you could write your own pretty easily.

If you upgrade to using TopLink 11g (preview), which you can download and use under the Oracle OTN license, then you have support for using cache invalidation and cache coordination. This functionality is also available in the Eclipse EclipseLink project currently in incubation.

---
James Sutherland

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