Our PRTG environment has 12,000 sensors of various kinds running on a Windows Server 2012 R2 VM with 6 cores and 12 GB of memory.
We've just upgraded the PRTG installation from v184.108.40.2062+ to 220.127.116.119 and it's taking quite a long time for all of our sensors to instantiate. Nearly all of them went green initially, then slowly dropped into an unknown state with a counter of 500+ "cache calculation" background tasks pending, and PRTG has been sitting in this state for quite some time now.
My understanding is that this happens because PRTG needs to recalculate its historical data cache every time it is updated or otherwise restarted. However, I'm not really clear on whether this is normal behavior or how long this recalculation is supposed to take for a given environment size. It seems somewhat unlikely that it's normal for PRTG to take literally hours to bring all of its sensors up after every restart - so I assume it's more likely that there's something out of place with our installation. We are already looking at decreasing historical data retention periods and lowering our average sensor polling intervals. Is there anything else we should be looking at?
I've read a few other KB articles on this question, but none of them have provided the kind of answer I'm looking for.