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WordPress Tutorial: Using WP-Cache on Windows / IIS

Is your blog starting to bog down? Getting nasty emails from your ISP about overloading the database server? Since most blogs are read far more often than they are updated, caching your pages can result in a real performance improvement.

Wordpress has some very basic object caching, but you really need to be able to cache whole pages to see a big benefit. Luckily there is a very good page-caching plugin, WP-Cache.

If you are on a Linux or Unix host, installation is pretty straightforward.

Now, what if you are on a Windows/ IIS host and using 'date and name based', almost-pretty permalinks? No sweat. Okay, a little bit of sweat.

The code for WP-Cache makes a few assumptions about the environment it's running in which don't work out so well in Windows. My first major step in getting it to work was a great blog post on CPUIdle. Since that blog seems to be down, I'll quote their steps here:

"1. Download WP-Cache zip file (current version as of writing is 2.0.17) and unzip into wp-content/plugins folder.

2. Copy wp-content/plugins/wp-cache/wp-cache-phase1.php to wp-content/advanced-cache.php (not really sure why this isn’t simplified by the author).

3. Open the standard wp-config.php file and add define('WP_CACHE', true);

4. Now comes the tricky part:

open wp-content/plugins/wp-cache/wp-cache.php in your favourite text editor. Search for the wp_cache_add_pages function and change the function code like this:

add_options_page('WP-Cache Manager', 'WP-Cache', 5, 'wp_cache/wp_cache.php', 'wp_cache_manager');

Reason the original code doesn’ work is that the original __FILE__ resolves to wp_cache\wp_cache.php which some browser eat and convert to wp_cachewp_cache.php- which doesn’t exist.

5. Second problem is that WP-Cache checks for installation step 2) in a windows-incompatible manner. Search for the wp_cache_check_link function. Change the first three lines after the variable declaration in this way:

# if ( basename(@readlink($wp_cache_link)) != basename($wp_cache_file)) {

# @unlink($wp_cache_link);

# if (!@symlink ($wp_cache_file, $wp_cache_link)) {

if (!file_exists($wp_cache_link)) { {

6. Finally, open wp-content/plugins/wp-cache/wp-cache-phase2.php and search for ob_end_clean(); and replace with ob_end_flush();. Without this change the cached page contents are not written back when the page is initially cached. It’s unclear to me if that works under *nix, I assume it couldn’t.

7. That’s it- you’re done. No goto Options/WP-Cache and turn caching on."

Unfortunately, if you are set up like we are, using the “index.php� style permalinks, there's one last step you're going to have to do. In Windows / IIS, $_SERVER['REQUEST_URI'] is blank. You need to use $_SERVER['SCRIPT_NAME'].$_SERVER['PATH_INFO'] instead. If you don't, WP-Cache will happily cache your index.php file, but it will also think your /index.php/category/cheese/ page and your /index.php/2006/01/01/I-am-very-interesting/ page are the same as index.php.

In wp-cache-phase1.php (and also advance-cache.php) look for this line:

$key = md5(preg_replace('/#.*$/', '', $_SERVER['REQUEST_URI']) . wp_cache_get_cookies_values());

and change it to this:

$key = md5(preg_replace('/#.*$/', '', $_SERVER['SCRIPT_NAME'].$_SERVER['PATH_INFO']) . wp_cache_get_cookies_values());

By the way, one nice thing about step 6 above is that it also fixes a blank-page bug that some people have run into.

Finally, what if you want to use both WP-Cache and gzip? Here's how.