Sysadmin

What are your strategies when a MySQL/MariaDB database server grows to have too much traffic for a single host to handle, i.e. scaling CPU/RAM is not an option anymore? Do you deploy ProxySQL to start splitting the traffic according to some rule to two different hosts? What would the rule be, and how would you split the data? Has anyone migrated to TiDB? In that case, what was the strategy to detect if the SQL your app uses is fully compatible with TiDB?