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From Daniel John Debrunner <...@debrunners.com>
Subject Re: multiple systems in same VM?
Date Thu, 07 Oct 2004 01:25:20 GMT
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.

Derby also supports (or will support once the first release with new
features is available) "soft-upgrade", allowing an application to use a
newer version of the engine without upgrade. Thus if two Derby
applications are running in a single JVM, one intended to run against
10.0 and one against 10.5, then the JVM can use the single 10.5 Derby
engine for both databases and applications.

Since Derby is just a jar file in embedded mode, it is like two
applications trying to use two different versions of a jar.


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