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From "Khin, Gerald" <G.K...@ids-scheer.de>
Subject RE: multiple systems in same VM?
Date Thu, 07 Oct 2004 08:32:48 GMT
Hi! 

> -----Original Message-----
> From: Daniel John Debrunner [mailto:djd@debrunners.com] 
> Sent: Donnerstag, 7. Oktober 2004 03:25
> To: Derby Development
> Subject: Re: multiple systems in same VM?
> 
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Khin, Gerald wrote:
> >
> > Is it planned to support multiple systems in the same VM? 
> Think of two 
> > or more java libraries from different companies each using derby as 
> > embedded database. I guess that they will hamper each other.
> 
> Technically derby supports a single system, which can 
> comprise of multiple databases, per class loader in a single 
> JVM. Typically the Derby libraries are on the class path and 
> thus are loaded by the system class loader leading to a 
> single system per JVM. Database instances can only be loaded 
> by one Derby system.
> 

What I meant to say is, that if two or more software supplier of some
nice java libraries decide to use Derby as an embedded database for some
internal reasons so that the user of these libraries should not be aware
of the existence of Derby usage, the conflicts will arise if the user of
the libraries uses them in a common application. And the more popular
Derby becomes (where I have no doubt at all), the higher the probability
that such a situation occurs.

The only resort I come up with is that a well behaving library, that
wants to use embedded Derby, must not try to hide its usage, or has to
do some classloader things. I think, the most convenient solution from
the Derby using developers point of view would be if Derby would provide
a concept that extends its current system concept to support multiple
systems.

> (snip)
> Dan.

Gerald
 

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