Pandora FMS infrastructure allows to have multiple servers both data and network to distribute the load and be able to manage the monitoring of more agents.
It is very important to optimize the MySQL to manage the available memory well and to have a MySQL with appropriated dimension to support the load.
There is also the option of setting up a MySQL cluster for both high availability and load sharing. See the documentation for more information:
https://pandorafms.com/manual/en/documentation/05_big_environments/06_ha