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Performance problems arrive from many sources, including faulty or insufficient hardware resources, inefficient SQL, contention between multiple sessions, and problems with the shared pool. The following sections in this chapter describe various performance issues and the systematic optimization methods to address those issues. (These methods were described earlier in 9.) We ve chosen four examples to look at: Inefficient SQL: This section begins a look into one of the most common performanceoptimization problems that a DBA faces, that of specific SQL statements that do not perform well. We begin by collecting data, verifying the problem, and determining whether the problem lies in the parse phase or the execution phase. Parse performance issues: Assuming the problem lies in the parsing phase, we look at some ways to further narrow and then resolve the problem. High execution time or fetch time issues: Often the problem with a poorly performing SQL statement is that it takes a long time to execute, to find and fetch the rows that it needs to return. In this section, we delve into this common trouble area, again looking at ways to apply methods from 9 toward finding a solution. Shared pool abuse: We end the chapter by looking at a class of problems resulting from poor management of the shared pool. We look at some possible solutions and at some guidelines for investigating root causes.

operating systems where Oracle is implemented with threads (such as Windows). In the context of this chapter, I use the term process to cover both processes and threads. If you are using an implementation of Oracle that is multiprocess, such as you see on UNIX, the term process is totally appropriate. If you are using a single-process implementation of Oracle, such as you see on Windows, the term process will actually mean thread within the Oracle process. So, for example, when I talk about the DBWn process, the equivalent on Windows is the DBWn thread within the Oracle process.

Now that you have a custom class for passing data in the second parameter of your event handlers, you need a delegate type that uses the new custom class. There are two ways you can do this: The first way is to use the nongeneric method: Create a new custom delegate, using your custom class type, as shown in the following code. Use the new delegate name throughout the four other sections of the event code. Custom delegate name Custom class public delegate void MyTCEventHandler(object sender, MyTCEventArgs e); The second way is new with C# 2.0, and uses the generic delegate EventHandler<>, which is also declared in the namespace System. To use the generic delegate, follow these steps: Place the name of the custom class between the angle brackets. Use the entire string, wherever you would have used the name of your custom delegate type. For example, this is what the event declaration would look like. Generic delegate using custom class public event EventHandler< MyTCEventArgs > Elapsed; Event name Use the custom class and the custom delegate, either nongeneric or generic, in the other four sections of code dealing with the event. For example, the following code updates the MyTimerClass code to use a custom EventArgs class called MyTCEventArgs and the generic EventHandler<> delegate.

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