Online non-stop software update using replicated execution blocks

Software updating is an inevitable process in the lifetime of a computer system. Numerous update mechanisms have been applied to software products. However, only little attention has been devoted to online nonstop software updating. Traditional update utilities typically require programs to stop execution during modifications, and this decreases the availability of the systems. For e-commerce (electronic commerce) companies, improving system availability implies increasing opportunities for greater business profit. Therefore, minimizing the system maintenance time for necessary software updates becomes a critical issue. This paper describes an approach to nonstop software updating. The approach composes a program using two replicated execution blocks. By switching between the execution blocks, the program can be modified without terminating its service. The paper also discusses the system environments that are required in order to support the approach