19.5.2.6 Change and test one area of code at a time

One of my biggest problems when I debug my code is that I am overconfident about my development and debugging skills, so I try to address too many problems at once. I make five or ten changes, rerun my test, and get very unreliable and minimally useful results. I find that my changes cause other problems (a common phenomenon until a program stabilizes, and a sure sign that lots more debugging and testing is needed), that some, but not all, of the original errors are gone, and that I have no idea which changes fixed which errors and which changes caused new errors.

In short, my debugging effort is a mess, and I have to back out of changes until I have a clearer picture of what is happening in my program.

Unless you are making very simple changes, you should fix one problem at a time and then test that fix. The amount of time it takes to compile, generate, and test may increase, but in the long run you will be much more productive.

Another aspect of incremental testing and debugging is performing unit tests on individual modules before you test a program that calls these various modules. If you test the programs separately and determine that they work, when you debug your application as a whole (in a system test), you do not have to worry about whether those modules return correct values or perform the correct actions. Instead, you can concentrate on the code that calls the modules. (See the earlier section Section 19.4 for more on unit testing.)

19.6 Tuning pl/sql Programs

Tuning an Oracle application is a complex process—you need to tune the SQL in your code base, make sure the System Global Area (SGA) is properly configured, optimize algorithms, and so on. Tuning individual PL/SQL programs is a bit less daunting, but still more than enough of a challenge. Before spending lots of time improving the performance of your PL/SQL code, you should first:

Tune access to code and data in the SGA

Before your code can be executed (and perhaps run too slowly), it must be loaded into the SGA of the Oracle instance. This process can benefit from a focused tuning effort, usually performed by a DBA. You will find more information about the SGA and the PL/SQL runtime architecture in Chapter 20.

Optimize your SQL

In virtually any application you write against the Oracle RDBMS, the vast majority of tuning will take place by optimizing the SQL statements executed against your data. The potential inefficiencies of a 16-way join dwarf the usual issues found in a procedural block of code. To put it another way, if you have a program that runs in 20 hours and you need to reduce elapsed time to 30 minutes, virtually your only hope will be to concentrate on the SQL within your code. There are many third-party tools available to both DBAs and developers that perform very sophisticated analyses of SQL within applications and recommend more efficient alternatives.

Once you are confident that the "context" in which your PL/SQL code is run is not obviously inefficient, you should turn your attention to the code base. I suggest the following steps:

Write your application with best practices and standards in mind

While you should not take clearly inefficient approaches to meeting requirements, you also should not obsess about the performance implications of every line in your code.Remember that most of the code you write will never be a bottleneck in your application's performance, so you don't have to optimize it. Instead, get the application done and then . . .

Analyze your application's execution profile

Does it run quickly enough? If it does, great—you don't need to do any tuning (at the moment). If it's too slow, identify which specific elements of the application are causing the problem and then focus directly on those programs (or parts of programs). Once identified, you can then . . .

Tune your algorithms

As a procedural language, PL/SQL is often used to implement complex formulas and algorithms. You can make use of conditional statements, loops, perhaps even GOTOs and (I hope) reusable modules to get the job done. These algorithms can be written in many different ways, some of which perform very badly. How do you tune poorly written algorithms? This is a tough question with no easy answers. Tuning algorithms is much more complex than tuning SQL (which is "structured" and therefore lends itself more easily to automated analysis).

Take advantage of any PL/SQL-specific performance features

Over the years, Oracle has added statements and optimizations that can make a substantial difference to the execution of your code. From the RETURNING clause to FORALL, make sure you aren't "living in the past" and paying the price in application inefficiencies.

It is outside the scope of this book to offer substantial advice on SQL tuning and database/SGA configuration. Even a comprehensive discourse on PL/SQL tuning alone would require multiple chapters. Furthermore, developers often find that many tuning tips have limited or no impact on their particular environments. In the remainder of this chapter, I will present some ideas on how to analyze performance of your code, and then offer a limited amount of tuning advice that will apply to the broadest range of applications.