WordPress.org

Why is WP-Super-Cache better than WP-Cache?

This plugin is based on the excellent WP-Cache plugin and therefore brings all the benefits of that plugin to WordPress. On top of that it creates copies of every page that is accessed on a blog in a form that is quickly served by the web server. It's almost as quick as if the you had saved a page in your browser and uploaded it to replace your homepage.

Will comments and other dynamic parts of my blog update immediately?

Comments will show as soon as they are moderated, depending on the comment policy of the blog owner. Other dynamic elements on a page may not update unless they are written in Javascript, Flash, Java or another client side browser language. The plugin really produces static html pages. No PHP is executed when those pages are served. "Popularity Contest" is one such plugin that will not work.

Why are there two expiry times?

WP Super Cache stores it's cached files in a different way to WP Cache that lets it work better even when there are very many cached files. That is why the Super Cache expiry time is so much longer by default. If your site starts to slow down and there are too many cached files reduce these times and change the garbage collection number too.

Will the Super Cache compression slow down my server?

No, it will do the opposite in fact. Super Cache files are compressed and stored that way so the heavy compression is done only once. These files are generally much smaller and are sent to a visitor's browser much more quickly than uncompressed html. As a result, your server spends less time talking over the network which saves CPU time and bandwidth, and can also serve the next request much more quickly.

How do I uninstall WP Super Cache?

1. Clear the cache in the backend page and then deactivate it on the plugins page.
2. Remove the Super Cache mod_rewrite rules from your .htaccess file.
3. Remove the WP_CACHE define from wp-config.php
4. Remove the files wp-content/advanced-cache.php and wp-content/wp-cache-config.php
5. Remove the directory wp-content/cache/
6. Remove the directory wp-super-cache from your plugins directory.

Troubleshooting

If things don't work when you installed the plugin here are a few things to check:

1. Is wp-content writable by the web server?
2. Is there a wp-content/wp-cache-config.php ? If not, copy the file wp-super-cache/wp-cache-config-sample.php to wp-content/wp-cache-config.php and make sure WPCACHEHOME points at the right place. "plugins" should be "mu-plugins" if you're using WordPress MU.

3. Is there a wp-content/advanced-cache.php ? If not, then you must symlink wp-super-cache/wp-cache-phase1.php to it with this command while in the wp-content folder.

   ln -s plugins/wp-super-cache/wp-cache-phase1.php advanced-cache.php
   

   If you can't do that, then copy the file. That will work too.

4. If pages are not cached at all, remove wp-content/advanced-cache.php and recreate it, following the advice above.

5. Make sure the following line is in wp-config.php and it is ABOVE the "require_once(ABSPATH.'wp-settings.php');" line:

   define( 'WP_CACHE', true );
   

6. Try the Options->WP Super Cache page again and enable cache.
7. Look in wp-content/cache/supercache/. Are there directories and files there?
8. Anything in your php error_log?
9. If your browser keeps asking you to save the file after the super cache is installed you must disable Super Cache compression. Go to the Options->WP Super Cache page and disable it there.
10. The plugin does not work very well when PHP's safe mode is active. This must be disabled by your administrator.
11. If pages are randomly super cached and sometimes not, your blog can probably be viewed with and without the "www" prefix on the URL. You should choose one way and install the Enforce www preference plugin.
12. Private Server users at Dreamhost should edit wp-content/wp-cache-config.php and set the cache dir to "/tmp/" if they are getting errors about increasing CPU usage. See this discussion for more.
13. semacquire() errors such as "failed to acquire key 0x152b: Permission denied in..." are a sign that you must use file locking. Edit wp-content/wp-cache-config.php and uncomment "$useflock = true" or set $sem_id to a different value.