Tag Archives: WordPress

WP Super Cache is a page caching plugin for WordPress that will significantly speed up your website.

If you’re not interested in the changes, simply grab the latest version of the plugin and copy the files into your plugin folder. It’ll work, but if you’re upgrading, you should read on.

Major changes in this release:

1. Generate a semaphore id based on hostname and cache path to avoid problems on shared hosts, props Tigertech.
2. If you run WordPress from a different directory to where it’s installed, supercached files weren’t deleted when a post was made or updated. That is now fixed. Thanks Viper007Bond for all your help on that.
3. Paged archives, category pages, and tag pages are now cleared when a post is edited or comment approved. This replicates what WP Cache did all along so you should hopefully see supercached static files updating more often.
4. If your .htaccess is read-only, the mod_rewrite rules are displayed on the admin page. Thanks Matt for the patch.
5. Updated mod_rewrite rules won’t serve static html files if there’s a “=” in the url. Should catch all sorts of problems with plugins and attachments. You’ll have to manually edit your root .htaccess to match the new rules.
6. Set cache control and expiry headers of supercached files. They are cached for 5 minutes, but with a “must-revalidate” header. Delete wp-content/cache/.htaccess for the new rules to be updated.
7. Check for WordPress MU because it can’t update the .htaccess file.
8. Write supercache html to temporary files and rename. The old way opened the correct file for writing, did some work and wrote the file. In the fraction of a second it took to write the file, someone might request it and get an incomplete page.
9. The Supercache expiry time has been removed. There can be only one.

Edit: 0.8.1 has just been released. This addresses the following:

• The “forbidden files” problems some users had is fixed.
• Supercache files were being removed needlessly when a moderated comment was made.
• I added a “Clear cached files when post is edited” checkbox.
• I added a “Delete Cache” link next to the Dashboard link on the dashboard.
• Tigertech found that when a file is renamed and the new filename is already used, the old remains.
• Updated readme.txt.

WordPress.org user, “definitelynot” discovered a bug in the WordPress plugin, WP Super Cache that could expose blogs to duplicate content penalties. Unfortunately this affects every blog that uses the plugin in “ON” or full “Super Cache” mode, and has URLs that end with the “/” (forward slash) character. If the plugin is on “half on” mode, you’ll be fine.

The problem is that an anonymous user might visit a legitimate URL, ending with a slash, the plugin then creates a static file out of that page, which is then used when people visit the same URL. Unfortunately if someone links to that URL without the ending slash, a visiting browser or search engine bot won’t be redirected to the proper URL, they’ll be served the static html file.

For example:

1. John visits the URL /2007/05/23/why-the-nurses-cant-go-on-strike/ on my site. WP Super Cache creates a html file of that page.
2. In his enthusiasm for that post, John publishes a post about those zany doctors, but he forgets the ending “/”.
3. Googlebot, seeing fresh content on John’s site, crawls it and sees the link, visits my site eventually and wonders why it’s seeing the exact same page at two different URLs.

To be fair, Google is pretty good at figuring out where duplicate content is supposed to go but it’s better to avoid the issue completely. It also only matters if there are links to your site without the ending slash. The most common will probably be to your homepage as it’s likely internal URLs will be copy/pasted.

How to Fix
You should update to version 0.7 of the plugin which checks if your blog is affected by this problem. It also has instructions for updating the mod_rewrite rules in your .htaccess. It’s fairly easy to fix. Thank you “andylav” for the mod rewrite magic!

1. Edit the .htaccess in the root of your WordPress install.
2. You’ll see two groups of rules that look like this:
   

   RewriteCond %{REQUEST_METHOD} !=POST
   RewriteCond %{QUERY_STRING} !.*s=.*
   RewriteCond %{QUERY_STRING} !.*wp-subscription-manager=.*
   RewriteCond %{QUERY_STRING} !.*attachment_id=.*
   RewriteCond %{HTTP:Cookie} !^.*(comment_author_|wordpress|wp-postpass_).*$
   RewriteCond %{HTTP:Accept-Encoding} .*gzip.*
   RewriteCond %{DOCUMENT_ROOT}/wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html.gz -f
   RewriteRule ^(.*) /wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html.gz [L]
   
   RewriteCond %{REQUEST_METHOD} !=POST
   RewriteCond %{QUERY_STRING} !.*s=.*
   RewriteCond %{QUERY_STRING} !.*wp-subscription-manager=.*
   RewriteCond %{QUERY_STRING} !.*attachment_id=.*
   RewriteCond %{HTTP:Cookie} !^.*(comment_author_|wordpress|wp-postpass_).*$
   RewriteCond %{DOCUMENT_ROOT}/wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html -f
   RewriteRule ^(.*) /wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html [L]
   
   

3. You need to add the following 2 rules above each block of “RewriteCond” lines:
   

   RewriteCond %{REQUEST_URI} !^.*[^/]$
   RewriteCond %{REQUEST_URI} !^.*//.*$
   
   

4. The rules should eventually look like this:
   

   RewriteCond %{REQUEST_URI} !^.*[^/]$
   RewriteCond %{REQUEST_URI} !^.*//.*$
   RewriteCond %{REQUEST_METHOD} !=POST
   RewriteCond %{QUERY_STRING} !.*s=.*
   RewriteCond %{QUERY_STRING} !.*wp-subscription-manager=.*
   RewriteCond %{QUERY_STRING} !.*attachment_id=.*
   RewriteCond %{HTTP:Cookie} !^.*(comment_author_|wordpress|wp-postpass_).*$
   RewriteCond %{HTTP:Accept-Encoding} .*gzip.*
   RewriteCond %{DOCUMENT_ROOT}/wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html.gz -f
   RewriteRule ^(.*) /wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html.gz [L]
   
   RewriteCond %{REQUEST_URI} !^.*[^/]$
   RewriteCond %{REQUEST_URI} !^.*//.*$
   RewriteCond %{REQUEST_METHOD} !=POST
   RewriteCond %{QUERY_STRING} !.*s=.*
   RewriteCond %{QUERY_STRING} !.*wp-subscription-manager=.*
   RewriteCond %{QUERY_STRING} !.*attachment_id=.*
   RewriteCond %{HTTP:Cookie} !^.*(comment_author_|wordpress|wp-postpass_).*$
   RewriteCond %{DOCUMENT_ROOT}/wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html -f
   RewriteRule ^(.*) /wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html [L]
   

5. Or you could just delete those rules and let the plugin regenerate them for you again.

PS. Thanks also to Lloyd for noticing the “enable the plugin” link was pointing at the wrong URL, and to Ryan who spotted a minor problem with the admin page and was kind enough to send me a Tweet about it.
PPS. I’ve just tagged 0.7.1 to fix some problems with the updating of the .htaccess, mainly for new users. If 0.7 of the plugin works for you, there’s no need to upgrade!