Is there any document to describe some answer my question above? 

RHQ database is growing quickly, we still need the measurements (at least some of them) - so we need to have some kind of backup, for case of server disaster.

I guess there should also be a few rules somewhere to set the time , for which the data should be kept in the live database.

Is it enough to backup the postgresql database to be sure I can restore a state, which isn't very old? If I have got a non-empty database, should I install, or upgrade RHQ?

Attila