This month in tech... before that, here's a testimonial for an open source project that you can't beat:
You could've been rich - My mother
Moving on, I heard about a persistence API called Carbonado on the Voldemort forums. It's an open source project from the Amazon guys. It's a no frills (read clean and simple) layer that works with Berkley DB and JDBC. It's even blessed by the BDB guys as a nicer layer on top of BDB.
An interesting thread going on between the Hotspot GC team and a HBase engineer facing some GC problems. Have a look at the new generation sizes they've used for some deployments, it was new to me.
If you want to OD on JVM options, there's a list for that too.
Some folks playing with the userland filesystem in Unix - FUSE. Voldemort, Github and all sorts of funny stuff as Filesystems. Reminds me of GDrive.
NoSQL systems are notorious for not being able to do simple Joins. Their answer is Map-Reduce. For running multi-attribute filtering, there's Merge-Join. Google's App Engine which is like a poor man's data store suggests the same (slide 30). I am skeptical of such queries that run on a cluster of machines, without any indexes, burning CPU on all machines, moving data back and forth. Can't imagine what it does to latency.