Dinamic aggregation on data with constraint

I want to resolve this general problem but I don't know exactly how. I have some data and an aggregator. (In my project I'm using Hazelcast Jet and Java). I have two device (A,B) monitored and two customer that watch a dashboard. The first can see only A and the second can see A,B. If A goes offline, the first will see 0 device on and the second will see 1 device on.

How Can I Aggregate data, based on customer visibility?

Potentially I could have 10000 devices and 1000 different customer visibility, so doing 1000 or more different query (aggregation) in realtime can be heavy on the system.

Is there a know pattern to manage this situation?

Thanks, Giovanni