This is an area in which I'm proud of Dejavu
The default Unit Server class has a "cache lifetime" value you can set; if a unit is not requested by client code within that period, it gets flushed out of the cache. Deployers can set a sweeper process to run every 5 minutes, every hour, every day, whatever they find is best--AND, can do that either at app startup with a config file, or just do it on the fly (OK, I haven't written the "on the fly" part yet, but it wouldn't be hard).
But the cool part IMO is that you don't have to use the default Server class or its default components. For example, I have a BurnedRecaller that, on the first request (even if its filtered), loads _all_ objects of that Unit class into the cache and keeps them there. You could just as easily make one that does no caching at all.
In other words, I tried to make testing and then using different cache strategies monkey-easy.
