Hot on the heals of thinking about information quality, I came across this little gem regarding Spring and JPA configuration:
"Using multiple session factories in a logical transaction imposes challenging issues concerning transaction management... We quickly abandoned [JTA transaction management] due to the potential cost and complexity of an XA protocol with two-phase commit. Since most of the modules of an application share the same data source, the imposed cost and complexity are definitively unnecessary."
The authors then go on to describe how they built a custom solution that causes the same database connection to be used by the modules, removing the need for transaction coordination across multiple connections.
"Extending Spring’s transaction management with SessionFactory swapping and the Shared Transaction Resource pattern was a very challenging task."
That last bit should probably have read "challenging and unnecessary task".
A good JCA will automatically track connections enlisted with a JTA transaction and will reuse the already enlisted connection to satisfy a further dataSource.getConnection() request. Further, even if it does enlist multiple connections, the JTA will use isSameRM to detect that they relate to the same resource manager and thus still maintain the one phase commit optimisation. All of these challenging tasks are taken care of for you by the application server.
You probably should not bother to invent a better mousetrap until you've determined that current mousetraps don't catch your mice. The imposed cost and complexity are definitively unnecessary.