Live Blog of “WordPress Caching” by Brandon Savage

From WordCamp Mid-Atlantic 2009 #wordcampmidatl

(slides per @brandonsavage)

• What is caching?
• Why we need caching?
• Improving your code’s performance
• Improving the content’s performance
• Building your own caching plugin

Things that you cache…

• code (HTML, sidebar)
• login status (sessions, username)
• content (MySQL queries)

Things you don’t want to cache…

• dynamic content
• user permissions
• passwords
• security settings

Why is caching important?

• Caching improves the speed of the page load.
• Caching reduces server load.
• 9,829 function calls to load WordPress!

WordPress by itself is extremely inefficient!

WordPress Performance Benchmarks:

• WordPress by itself (with plugins):  almost 6 seconds
• APC enabled (without WP-Cache):  about 2 seconds

Caching the code

• Opcode cache

1. PHP is not a complied language; code is compiled and executed at run time.
2. Compiling code takes extra time, extra CPU, and extra resources.

• Benefits of Opcode Cache
• Drawback of Opcode Cache

1. Still must invoke PHP (which requires resources)
2. Executes “expensive” stat() calls.
3. Doesn’t play nice with some WordPress caching systems (e.g. WP-Cache)

Bottom Line:  You’re crazy if you don’t have an Opcode cache!

Caching the content

Why cache content?

• Most blogs don’t have content changes that often.
• Cached content reduces server load and increases delivery.
• When high traffic shows up, you’ll be ready.

Typical WordPress process

• WordPress loads the plugins, then the theme, then the content and returns the page to the user.

With WP-Cache

• Checks for a cached file.
• If found, it serves the cached file and terminates WordPress.
• If not, it continues on with typical process and caches.

WP-Cache is a file-based cache.

File based caches:

• Write directly to the disk, and read directly from the disk.
• This can be slow, as a disk read is required.
• This can be more reliable, as the files persist after Apache or MySQL start.

Drawbacks of WP-Cache

• File based cache (slower)
• Might have thousands of files
• WP-Cache still required the PHP parser
• WP-Cache evaluated the file before it serves it

Preparing for the Digg Effect

• WP-Super-Cache

1. Uses same code as WP-Cache
2. Replaces dynamic page hyperlinks with static HTML page hyperlinks
3. Removes the need for PHP parser

The rule of web servers: Static always beats dynamic.

Warning! If you used WP-Cache, it created a symlink for advanced-cache.php.

Words of caution…

• WordPress has not initialized a databse connection or the WordPress framework at the cache execution time.