Of course one does not simply rewrite an existing system, but for what it's worth, you could still make that fast to query by doing xml or json queries with sub

Of course one does not simply rewrite an existing system, but for what it's worth, you could still make that fast to query by doing xml or json queries with subselects. Some testing I've done with that technique with a mock social-media use-case hit ~15k requests/second end-to-end on pretty weak hardware (4 cores) needing to query 8 tables to construct a profile with 1M profiles in the database. I don't have the exact results saved, but IIRC it was a ~10 ms response time under load.