I've setup up a Utilization Memory graph in zabbix. This graph has 2 items: total memory and used memory. The total memory item type is zabbix agent and used memory is a calculated item that results of the calculation of total memory minus free memory. Zabbix frontend is very slow to load this kind of graph comparing with all my other graphs with no calculated items in them. I've made other tests with other graphs with and without calculated items and the conclusion is the same. It could be a database issue? Maybe an index missing?