[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [dist-obj] Fw: [dist-obj] Why use Application Servers?
on 3/22/00 7:51 PM, Kevin Dick at kevin@dick.org wrote:
>> Roger Sessions wrote:
>> [snip]
>> 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
>
> Your knowledge may be somewhat out of date with regards to the EJB
> vendors. I know that both Persistence and GemStone have cross machine
> cache coherency. I believe Persistence also has a framework for
> updating the cache in the face of outside database updates based on
> triggers and TIB/Rendezvous. GemStone may well have something similar,
> but I don't know for sure.
Here's my understanding... If you're using an RDBMS with GemStone, you'll
have to write your own way to detect & propagate those changes to the gs
repository. This may change in v 4.0, but I'm not sure. So, for multiple
applications on the same gs repository, everything is peachy... though
unfortunately not widely useful when most legacy applications talk to
RDBMS'...
If you have a distributed Gemstone system, it will keep coherency between
the shared page caches on the different nodes. (This seems to satisfy
Roger's second requirement.)
Persistence does seem to have a more advanced mechanism. I believe there
are public bindings available if you don't want to use TIB/Rendezvous as the
the communication bus.
Stu
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