What exactly is stored in the DB?
How often is the DB written to?
Is there a paper that explains why the DB is needed exactly, and what it stores?

Any good links available? I'm having trouble finding data - maybe my search terms are not working well!

In relation to another question posted about HA.
If I can figure out how often the DB is used, I can decide how to provide redundancy across sites. If there isn't much data written, but more read, then there isn't too much of a problem for me.