i_ReservationRequiredThreshold
The purpose of promotion code reservations is to ensure a good shopper experience when the number of promotion codes available is limited. This prevents a situation where a shopper enters a promotion code, sees the system accept it, but then the promotion code becomes unavailable at checkout time due to the promotion code limit being reached. However, reservations demand increased database writes and are not required for unlimited usage promotion codes or when the number of promotion codes available is large enough to support all concurrent shoppers. When the number of promotion codes available for a given limited usage promotion code falls below this threshold limit, the system starts enforcing reservations for that promotion code. While the number of codes remaining available for use is greater than this number, no reservation is granted for the promotion code. If you are having difficulty defining a value for this setting, choose a number that approximates the peak number of shoppers on the site at any given time. You can disable promotion code reservations by setting this value to zero, but we do not recommend this action.
The default value is 100 codes; there is no upper limit. If you provide a negative number, the default value is used.