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Oracle Performance Tuning and Optimization
The GUI/Server ModelThe next major step in the evolution of computing came when application vendors started to develop Graphical User Interfaces (GUIs) for their applications (see Figure 33.3). Although some people call this kind of computing client/server, I do not. I think that for a system to be considered a client, it must have more than just presentation services.
Many of these GUI/server applications do nothing more than their terminal counterparts didthey just added a pretty border or the ability to pull down menus with the mouse rather than with a keystroke. In fact, many graphical applications have a terminal-based or character-based version that has the exact same functionality. Many early GUI development tools were notorious for building a pretty screen but generating horrible SQL code. The SQL statements they generated were very inefficient and often generated much unnecessary CPU and network processing. Much of the problem was caused by the fact that the development tool generated code that was interpreted by another application that ran on the client. This arrangement was very inefficient and slow. It was not uncommon for complaints from users to result in the discovery that a 10-second response time was caused by 2 seconds in the RDBMS and 8 seconds in the GUI. Fortunately, todays tools are much more efficient. The addition of the GUI to applications changed the way people looked at applications but was not a great leap in technology. The real revolution occurred when these client machines started to do more than just present the data to the user. The Client/Server ModelThe client/server came of age when the client actually started doing work. Allowing the client to offload work from the server does help somewhat, but the real benefit of client/server computing is the addition of new functionality that was impossible in the past. The client/server machine allows many new and traditional functions to be performed on the client machine (see Figure 33.4).
In general, these client functions have very little to do with the actual display of the data (in contrast to the GUI/server model, which affected only the display of data). These additional functions have more to do with processing the data to be displayed, validating input values, performing local table lookups, and so on. Here is a list of some of the functions that the client in a client/server environment can perform:
When comparing client/server systems to GUI/server systems, consider the functionality of the client. By offloading work to increasingly more powerful clients, the performance of the entire system can be improved. As you see later in this chapter, it is also possible to offload the power of the server to a second-tier system.
Two-Tiered and Three-Tiered ModelsFrom the client/server computing model have evolved two different types of computing models: the two-tiered model and the three-tiered model. The two-tiered model is more like the traditional client/server model; the three-tiered model adds a level of processing known as the application server, which handles some of the functions of the client as well as some of the functions of the server. Two-Tiered SystemThe two-tiered system is the traditional client/server system described earlier in this chapter. This system consists of one or more servers and a client. The client system runs part or all of the application; the server provides the RDBMS functionality. This traditional client/server system is shown in Figure 33.5. In this manner, the client and the server work together to provide the needed functionality to the user community.
This model is typical for most client/server configurations today. However, I believe that many new client/server applications will soon move to the three-tiered model, described in the following section.
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