First of all you should check the monitoring package for OpenACS 4. It includes cassandracle and watchdog and has *not* been ported to PG, unfortunately. I think you could take standalone ports of those tool and easily drop them into the OpenACS 4 framework, giving folks the option of running them within a site or standalone.
Cassandracle can't really be fully ported to PostgreSQL because it doesn't keep track of all the necessary stats. I think PG 7.2 adds to the stats kept, though, and since our "next" (not 4.5) release of OpenACS 4 will be based on PG 7.2, I think you could do your work assuming PG 7.2's available.
Also ... talk to Roberto, just yesterday he was asking about the aD server architecture and the documents. I think he'll be excited to hear that you've begun work on what could be the basis for an OpenACS Server Architecture.
