I activate the mysql query loggin to see exactly what mysql is doing.
I made it on a test server which has a backup of a database and no zabbix server runnig.
I create a test screen which as no elements on it.
When I open it, then i look at the query log.
36425 query logged
34965 query like : Select * from host where hostid=10xxx"
It may be a little bit havy no ????