thanks for your input and tips! I´m always interested to see how other people set up large scale monitoring with cacti.
I did check out multiserver but it doesn´t really work across WAN-links when you have 2 seperate RRD-Caches.
Our setup has roughly 1.2k hosts and about 20k DSs but so far I´ve never run across DB-Perfomance issues tbh.
I avoided the boost plugin so far since we were able to put all RRDs into RAM-drive, so polling cycles are about
9-20s (including all sorts of scripts like WMI). The only tweaks I applied are some DB-synchronisations between my 2 Cacti-Servers (hosts, tree, etc.).
If we ever run into DB issues I´ll be sure to revisit your entry