In the past two days, I've seen two references to Practical PHP Programming, an online book that serves both as an introduction to programming with PHP5 and MySQL as well as a good advanced reference with many good tips.

This evening, I was browsing through the Performance chapter (chapter 18), and found a number of cool things, both for PHP and MySQL. Many were common sense things that I've been doing for a while, but which I've also seen and shaken my head at in code I've seen from others (calculating loop invariables at every iteration, not using variables passed to a function, not returning a value from a function, not using a return value from a function). Others were new and gave me pause for thought (string concatenation with the '.' operator is expensive, especially when done more than once in an operation; echo can take a comma separated list).

Some PHP myths were also dispelled, some of which I've been wondering about for awhile. For instance, the amount of comments and whitespace in PHP are not a factor in performance (and PHP caching systems will often strip them out anyways); double quotes are not more expensive than single quotes unless variable interpolation occurs.

It also has some good advice for SQL optimization, and, more importantly, MySQL server optimization. For instance, the author suggests running OPTIMIZE TABLE table; on any table that has been added/updated/deleted from to any large extent since creation; this will defrag the table and give it better performance. Use CHAR() versus VARCHAR(); VARCHAR() saves on space, but MySQL has to calculate how much space was used each time it queries in order to determine where the next field or record starts. However, if you have any variable length fields, you may as well use as many as you need — or split off variable length fields (such as a TEXT() field) into a different table in order to speed up searching. When performing JOINs, compare on numeric fields instead of character fields, and always JOIN on rows that are indexed.

I haven't read the entire book, but glancing through the TOC, there are some potential downfalls to its content:

• It doesn't cover PhpDoc It doesn't appear to cover unit testing Limited
• coverage of templating solutions (though they are mentioned) Limited usage of
• PEAR. The author does mention PEAR a number of times, and often indicates that use of certain PEAR modules is preferable to using the corresponding low-level PHP calls (e.g., Mail and Mail_MIME, DB), but in the examples rarely uses them.
• PHP-HTML-PHP… The examples I browsed all created self-contained scripts that did all HTML output. While I can appreciate this to a degree, I'd still like to see a book that shows OOP development in PHP and which creates re-usable web components in doing so. For instance, instead of creating a message board script, create a message board class that can be called from anywhere with metadata specifying the database and templates to use.

All told, there's plenty of meat in this book — I wish it were in dead tree format already so I could browse through it at my leisure, instead of in front of the computer.