How is Transaction Processing System affect performance of e-commerce sites?

Transaction Processing System influences performance of e-commerce sites:

Transaction-Processing applications characteristic Online-Transaction Processing Applications (OLTP), also termed as mission-critical applications, comprise order entry, point-of-sale systems and inventory.

This type of mission-critical system should run continuously, when it is unavailable still for a brief instant, the organizations will experience server repercussions.

Illustrations are stock exchange system, airline reservation systems and air traffic control networks.
Within a simple client/server system, several clients issue requests and server responses.