Web Database Applications with PHP, and MySQL

When to Use Sessions

So far in this chapter we have described how to implement stateful applications using sessions, but we have not discussed when they should or should not be used. Sessions allow some kinds of applications to be developed that otherwise would be difficult to implement on the Web. However, because HTTP is a stateless protocol, building a stateful application can present problems and restrictions. Avoiding the need to maintain state information is often a desirable goal. In this section we list some reasons sessions are used and some reasons to avoid them.

Reasons to Use Sessions

Sessions can be used in web database applications for several reasons. Many traditional database applications use sessions to help control user interaction, while other applications use sessions to reduce server processing.

Performance

In a stateless environment, an application may need to repeat an expensive operation. An example might be a financial calculation that requires many SQL statements and calls to mathematics libraries before displaying the results on several web pages. An application that uses a session variable to remember the result exposes the user, and the server, to the cost of the calculation only once.

Sequence of interaction

Often a database application—or indeed any application—needs to present a series of screens in a controlled order. One style of application—known as a wizard —guides a user through what would otherwise be a complex task with a series of screens. Wizards ...