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Date: Wed, 23 Nov 2005 12:01:15 -0800
From: "David W. Van Couvering" <David.Vancouvering@Sun.COM>
Subject: Support multiple Derby systems in one VM
To: Derby Development <derby-dev@db.apache.org>
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I also wanted to share an idea to help move us towards the larger 
problem supporting multiple Derby systems within the same VM (currently 
that's not possible).

The idea is that we have a new public class called DerbySystem that's in 
it's own package.  This is basically a data source factory for a given 
Derby system, each with its own classloader.  So in the same VM I could 
do something like

// Note the properties could be loaded from a config file rather
// than hardcoded in the source
Properties propsA = new Properties();
propsA.setProperty("derby.system.home", "/path/to/system/a");
propsA.setProperty("derby.system.classpath",
"/home/derby/10.1/derby.jar");
DerbySystem systemA = new DerbySystem(propsA);

Properties propsB = new Properties();
propsB.setProperty("derby.system.home", "/path/to/system/b");
propsA.setProperty("derby.system.classpath", "/home/derby/10.2/derby.jar");
DerbySystem systemB = new DerbySystem(propsB);

DataSource dsA = systemA.getDataSource("jdbc:derby:wombat;create=true");
DataSource dsB = systemB.getDataSource("jdbc:derby:wombat;create=true");

Connection connA = dsA.getConnection();
Connection connB = dsB.getConnection();

Note that for this to really work we need to fix Derby so that there are 
no hardcoded uses of system properties, but instead all code uses a 
service to obtain configuration properties for a given system.

David

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