A modern payment gateway must be available to its customers around the clock. Some issues can cause interruption of stable functioning of a payment gateway. In order to prevent such issues several mechanisms are applied. These mechanisms include internal auditing system and so-called transaction velocity tracking. Internal audit can be based on analysis on log files of various subsystems, or on constant pinging of payment gateway components. Transaction velocity tracking includes monitoring of payment gateway behavior in terms of transaction volumes processed through particular MIDs or integrations. If some deviations from traditional behavioral patterns occur, they might signify connection problems, or issues experienced by some clients. MID-based transaction velocity tracking is more appropriate for desktop applications. POS-based velocity tracking is good for large servers in charge of many merchants.
More information about payment gateway monitoring mechanisms is available in the respective article on #Paylosophy.