Been in the marked for an embedded Java database technology and have started playing with hsqldb. I’ve gotta say it’s a very nice little tool. Uses JDBC, writes to text files, and the SQL support is way beyond what I expected (including referential integrity!). Comes with a couple of nice little admin tools to boot!
I’ve given it a hammering with JMeter, and whilst it’s nowhere near as performant as MySQL (~200 transactions/minute vs ~12000 transactions a minute on the same hardware with a 10 user load), for embedded apps it’s just awesome. I’m wanting to use it as a scratch database for Unit testing which it will be ideal for. Great job guys!