[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[dist-obj] Fw: [dist-obj] Why use Application Servers?

Anne writes...
> If you are concerned about scalability, then I recommend that you get an
> application server that supports share object caching -- this technology
> (essentially using an in-memory object database in the middle tier) will
> allow an application server to support hundreds of thousands of concurrent
> users. Examples are Secant Extreme, Persistence PowerTier, GemStone/J, and
> application servers that support eXcelon Javlin and Versant Enterprise
> Container.

I think caching in the middle tier could work if it was done correctly, but
to the best of my knowledge, none of the major EJB vendors do it correctly.
In other words
- they don't notify the cache if an outside application updates the database
- they don't have a mechanism for cross machine middle tier cache coherency
(between the same EJB vendor working on two machines)
- they don't have a mechanism for cross EJB cache coherency (between two
different EJB  vendors)
Without such mechanisms, I see object caches as creating a high risk of
database corruption. If people are interested in this issue, I discussed it
in the ObjectWatch Newsletter #24 www.objectwatch.com/issue_24.htm

By the way, Microsoft had a similary type of middle tier data cache in the
Beta version of COM+, but fortunately they removed it before product
shipment. It had all the flaws of the EJB object caches, and I was opposed
to it for the same reasons I am opposed to the EJB caches. It was called
IMDB (In Memory DataBase). Their future plan is to integrate this into
SQLServer, where, in my opinion, it belongs. Caching is a database issue,
not a Component Oriented Middleware (EJB, COM+, etc) issue.

Best wishes to all,
Roger
---------------
Roger Sessions
President, ObjectWatch, Inc.
Training in Web Commerce Development
512/258-4922 roger@objectwatch.com http://www.objectwatch.com


==========================================================================
To manage your subscription, mailto:dist-obj-help@distributedcoalition.org 
Archives, FAQ, etc.     http://www.distributedcoalition.org/mailing_lists/