Rudder

Server group are dynamics, and so for a given group, we have to process some query, what can take a lot of time, to know the list of server in that group.
But we often need to know the list of group a given server belong to (without processing ALL group)

So, basically, it's adding a cache (ie a preprocess data) somewhere, and add some logic to update / invalidate it when needed.
There is two entry point (I think):
- in group query entries, add "list of matching server"
- in server entries, add "list of matching target".
In each case, the list is updated when a server is modified (added/updated/deleted) or when the query is modified.