Designing And Coding Scalable Applications - MACROMEDIA COLDFUSION 4.5-ADMINISTRING COLDFUSION SERVER Manual

Chapter 6: Creating Scalable and Highly Available Web Sites
dependencies between related but heterogeneous technologies. This section describes
some of the major issues affecting successful scalability implementations.
Note
This section discusses the following topics:

Designing and coding scalable applications

Avoiding common bottlenecks
DNS effects on Web site performance and availability
Load testing your Web applications
Designing and coding scalable applications
Application architects must create designs that are inherently flexible by relying upon
open standards that don't restrict the application's construction and implementation
to vendor-specific interfaces and tools. Similarly, the Web developers that construct
the designed application must be aware that they can significantly impact the
application's scalability in the way in which they write their code, build their SQL
queries, invoke thread management, access databases, and partition the application.
This section discusses the following topics to consider when designing and building a
Web application:
Application session and state management
Single threaded vs. multi-threaded application connections
Database locking and concurrency issues
Application partitioning
Application session and state management
As you create Web applications, you will likely create specific variables that you intend
to carry across multiple interactions between a user's browser and a site's Web
server(s). Using client variables that get stored in a shared state repository or session
variables that get stored in memory of a specific server are popular approaches for
accomplishing this. The latter approach, however, introduces a significant challenge
for a Web site that is supported by multiple servers. Once a user has begun a session
and variables are stored on a specific server, the user must return to that server for the
life of the session to maintain correct state information.
A good example that illustrates this concept is an e-commerce application that uses
shopping carts. With this type of application, as a customer accumulates items in his
or her cart, there must be a mechanism that ensures that the user can see the items as
they are added. One approach is to store these items in session variables on a specific
Web server. However, if you use this approach, there must also be a way to ensure that
Although your immediate role and responsibilities as an administrator
may not encompass all of the areas and issues described in this section,
you can share the information with relevant members of your
organization to help ensure successful development efforts.
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