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From David Van Couvering <David.Vancouver...@Sun.COM>
Subject Re: Multiple systems in same VM -- does this really work?
Date Wed, 04 May 2005 23:11:56 GMT
I think this might be a high-priority issue; I can see that a lot of 
uses of Derby will be within a container-based environment.  Multiple 
systems each with multiple databases could become a common configuration...


Jeremy Boynes wrote:

> David Van Couvering wrote:
>> Hi ,all.  I am getting questions we could use Derby inside a container 
>> such that each application in the container could have its own 
>> separate configuration.  In particular, it would be nice if each 
>> application (which often has its own classloader) could store its 
>> database files in a different location.
>> Based on previous discussions with Dan, my understanding is that 
>> conceptually you can have multiple Derby systems in a VM if you have 
>> each system created by a different classloader.  But since Derby 
>> system -wide properties are set using Java system properties, I don't 
>> think this could actually work.  Isn't it true that any  system-wide 
>> configuration (done either through -D or through System.setProperty) 
>> will apply for all Derby systems in the same VM?  Or does a system 
>> property apply only for the classloader of the class calling 
>> System.setProperty()?
>> Help here would be much appreciated.   I searched the Java SDK source 
>> code, but the method to load properties is a native method, and I 
>> can't find the native method source.  The fact that it *is* a native 
>> method, however, makes me suspect that system properties are VM-wide 
>> and not just classloader-wide.
> We have the same issue embedding Derby in Geronimo. The use of global 
> system properties is a real problem for us, not only because it 
> precludes multiple instances in the same JVM but also because it makes 
> the interface to JMX harder.
> Several people have asked for alternative configuration mechanisms. 
> However, this is a systemic issue for Derby and probably not easy to 
> change.
> -- 
> Jeremy

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