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To access the contents, click the chapter and section titles.
Oracle Performance Tuning and Optimization
Tuning MethodologyThis section explains why it is important to follow a structured, goal-oriented methodology in your tuning efforts if you want to achieve optimal results. The methodology I use involves these five steps as shown in Figure 4.1.
The following sections describe each of these steps individually and explain why each step is important to the final outcome. Sometimes, there are situations for which you dont have an answer to the problem or perhaps you dont even know what the problem is. In the long run, however, a little analysis is worth more than a lot of trial and error. Examine the ProblemThe first phase in tuning the system should always be the determination phase. First, see whether you even have a problem. You may just be at the limits of the configuration. To make sure, examine the system, look for problems, and make this determination logically. The determination phase consists of examining the system as it currently is, looking for problems or bottlenecks, and identifying hot spots. Keep in mind that performance problems may not always be obvious. Here is a partial list of some areas you should examine:
I prefer to categorize performance issues into the following three classes:
For the first class of problem, you may have to take drastic action. Tuning may solve the second class of problem. For the third class of problem, you need take no action. Here are some questions to ask yourself when examining the system and searching for problems:
If you answer yes to any of these questions, you may be seeing some performance problems that can be fixed. In some cases, you have reached the limitations of your hardware and should add an additional CPU or perhaps some more disks. If you answer no to all these questions, your system may be running very well. However, you should still periodically monitor the performance of the system to avoid future problems. Determine the ProblemOnce you have decided that there is some sort of problem in the system, make a careful analysis to determine the cause of the problem. At first glance, it is not always obvious what the problem is. You may see excessive disk I/O on a certain table that may lead you to believe you have an I/O problem when, in fact, you have a cache-hit problem or an index problem that is causing excessive I/Os. Take a few minutes to think about the problem. Decide what area you believe the problem to be in. Thinking through the problem can help you avoid a long trial-and-error period in which you randomly try different things without positive results. At this stage, note-taking is a must. By writing down your ideas and thoughts, you can better organize them. If you have to go back and rethink the problem, your notes will be very useful.
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