Hi Sebastian,
But the most important thing for me is, if I get any trouble if both radius servers will write their accounting records into the same database.
I'm not running postgres, but the concepts are the same. I set up a mysql replication (every dbms is slave of the other one) and one virtual ip which i configured in FR. When one server goes down the other takes the virtual ip address and continues to respond to radius requests. Accounting is consistent since both databases replicate each other. Uniqueness of accounting entry (remember that we have an auto_increment field in the radacct table) is guaranteed using different step increment values for the two dbms: the first server starts at 1 and increments two units (so: 1, 3, 5, ...), while the second server starts at 2 and increments two units (so: 2, 4, 6, ...).
Sebastian
I hope this helps, Sorry for my poor english, Francesco Cristofori.