Why
Initially, all the Extension (PX or CX) tables were stored in 1 physical table in MySQL and the database engine was not performing well with big amounts of records. As the data was growing, api.find("PX")/api.find("CX") became slower. Also the customer was getting timeouts in the UI. Database operations (like data correction) were almost impossible. Therefore the PX/CX tables were split into several physical database tables depending on the number of columns (for example, PX3, PX6, PX8, PX10, PX20, PX30, PX50). Choosing the right PX/CX size helps you to reduce the size of the physical table, so it is mandatory that you use the appropriate size and not e.g. PX30 for everything.
Currently, this is applicable for dedicated instances only.