Cache in dnn can be done in memory , Data base and Memory that i have read Memory Cache is the best . dnn implement Cache in page level and module level

now i have some question in mind :

1- if page output cache is enabled and set to 1800 sec , and one module in page set output cache to 1200 sec , which one has Priority ?

2- if out put cache for page that has query string is enabled , pages show same data for all query . 

 for example : http://abc.com/page/ should be cached but http://abc.com/page/Queryone/Querytwo ( or other ) should not be cached .

how it implemented in dnn?

3- i am using dnn 9.0.1 . i think that cache working better in dnn8 . in new dnn cpu load is high and query SQL with all Request . how can i found what is going wrong and why dnn query database with each request ?

- I have enabled page output cache in memory but i think that again data are fetch from database. how can i know that output is cached or fetch from database ?

i see this error in log file :

2017-02-22 00:15:50,446 [WIN-MA182KN2LA7][Thread:30][ERROR] DotNetNuke.Services.Exceptions.Exceptions - System.NullReferenceException: Object reference not set to an instance of an object.

   at DotNetNuke.UI.Modules.ModuleHost.TryLoadCached()