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From: Andrus Adamchik <andrus@objectstyle.org>
Subject: Derby as desktop database 
Date: Thu, 29 Jun 2006 10:45:07 +0100
To: derby-dev@db.apache.org

I've been looking for some time for a good embedded database that  
would work for desktop applications. Derby is ideal for that and I am  
starting to use it more and more in various examples and tutorials  
that I am writing for Cayenne. But there is one feature that I am  
missing in Derby (or any other database for that matter) - an ability  
to share the same database between multiple desktop applications (or  
multiple VM instances of the same Java application).

I asked this question the Derby folks from Sun at ApacheCon in Dublin  
the other day and the answer was basically - run the network server.  
In other words db sharing and embedded mode are not compatible. So I  
wonder what it would take to make it compatible?

Since we are talking desktop apps, the following conditions are at play:

(a) all apps run on the same machine (but in different VMs)
(b) usually only one instance at a time would work with the database,  
but other instances can occasionally access the db in the background  
(no need to deal with massive concurrency)
(c) usually the database is small-to-medium size.

Any ideas? One possible solution is cloning the DB for each instance  
and using multicast for peer-to-peer synchronization.

Another (more promising) is to do collaborative peer-to-peer  
connection pool (DataSource), so that when a client needs a local  
Derby connection it sends a multicast so that current lock owner in a  
different VM can finish its thing, shutdown Derby and release the  
lock. I wonder if anyone has done that already?

Andrus

------------------------------
Andrus (aka Andrei) Adamchik
Cayenne Persistence Framework
Creator, Committer
http://incubator.apache.org/projects/cayenne.html