I've written a couple of data layers for small apps, they're rough at the edges, but fine for the apps.
I'm looking at adding to the code with a view to scaling them, for example using transactions that will be robust across multiple databases.
Also of great interest to me is concurrent access / updates, and the sorts of defences that can be implemented. I can think of at least two further models for achieving such defences (one that holds a connection open during and one that doesn't), and want to compare my thinking against the thinking of others.
I did some searches on google, and looked through the Sun documentation for patterns. All I seem to be able to find are countless examples of data layers that deal JUST WITH RETRIEVING DATA.
To be honest they're all good and well but this helps little with the harder problems posed by administering data.
Does anyone have any good practical (i.e. with example code) sources for data layer designs / patterns?