Chapter 28. Efficiency and Debugging

Topics in This Chapter

• Optimization

• Measuring Performance

• Optimize the Slowest Parts

• When to Store Content in a Database

• Debugging Strategies

• Simulating HTTP Connections

• Output Buffering

• Output Compression

• Avoiding eval

• Don't Load Extensions Dynamically

• Improving Performance of MySQL Queries

• Optimizing Disk-Based Sessions

• Don't Pass by Reference

• Avoid Concatenation of Large Strings

• Avoid Serving Large Files with PHP-Enabled Apache

• Understanding Persistent Database Connections

• Avoid Using exec, Backticks, and system If Possible

• Use php.ini-recommended

• Don't Use Regular Expressions Unless You Must

• Optimizing Loops

• IIS Configuration

This chapter touches upon some issues of efficiency and debugging, which are more art than science. Efficiency should not be your first concern when writing code. You must first write code that works, and hopefully your second concern is keeping the code maintainable.

You will pick up some tactical design issues as you gain more experience in programming. These begin to gel as idioms—repeated structures applied to similar problems. Individuals and organizations tend to develop their own idioms, and you will notice them in code found in magazine articles and code repositories. Once you accept an idiom as your own, you can consider it a solved problem. This consistency saves time when writing code and when reading it later.

In most projects, a tiny minority of code is responsible for most of the execution time. Consequently, it pays to measure first and optimize the slowest section. If performance increases to acceptable levels, stop optimizing.

When a bug appears in your script, the time you spent writing meaningful comments and indenting will pay off. Sometimes just reading over troublesome code reveals its flaws. Most of the time you must print incremental values of variables to understand the problem.

Among the many books on the subject, I can recommend two. The first is Writing Solid Code by Steve Maguire. It's oriented toward writing applications in C, but many of the concepts apply to writing PHP scripts. The other is The Practice of Programming by Brian Kernighan and Rob Pike; Chapter 7 will be of particular interest.