If you choose "Mod Rewrite caching", mod_rewrite rules will be inserted into your .htaccess file. Look in your web root directory for this file. It should look similar to this:
-----------------.htaccess-----------------
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_METHOD} !=POST
RewriteCond %{QUERY_STRING} !.*=.*
RewriteCond %{HTTP_COOKIE} !^.*(comment_author_|wordpress|wp-postpass_).*$
RewriteCond %{HTTP:Accept-Encoding} gzip
RewriteCond %{HTTP_USER_AGENT} !^.*(2.0\ MMP|240x320|400X240|AvantGo|BlackBerry|Blazer|Cellphone|Danger|DoCoMo|Elaine/3.0|EudoraWeb|Googlebot-Mobile|hiptop|IEMobile|KYOCERA/WX310K|LG/U990|MIDP-2.|MMEF20|MOT-V|NetFront|Newt|Nintendo\ Wii|Nitro|Nokia|Opera\ Mini|Palm|PlayStation\ Portable|portalmmm|Proxinet|ProxiNet|SHARP-TQ-GX10|SHG-i900|Small|SonyEricsson|Symbian\ OS|SymbianOS|TS21i-10|UP.Browser|UP.Link|webOS|Windows\ CE|WinWAP|YahooSeeker/M1A1-R2D2|iPhone|iPod|Android|BlackBerry9530|LG-TU915\ Obigo|LGE\ VX|webOS|Nokia5800).*
RewriteCond %{DOCUMENT_ROOT}/wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html.gz -f
RewriteRule ^(.*) /wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html.gz [L]
RewriteCond %{REQUEST_METHOD} !=POST
RewriteCond %{QUERY_STRING} !.*=.*
RewriteCond %{QUERY_STRING} !.*attachment_id=.*
RewriteCond %{HTTP_COOKIE} !^.*(comment_author_|wordpress|wp-postpass_).*$
RewriteCond %{HTTP_USER_AGENT} !^.*(2.0\ MMP|240x320|400X240|AvantGo|BlackBerry|Blazer|Cellphone|Danger|DoCoMo|Elaine/3.0|EudoraWeb|Googlebot-Mobile|hiptop|IEMobile|KYOCERA/WX310K|LG/U990|MIDP-2.|MMEF20|MOT-V|NetFront|Newt|Nintendo\ Wii|Nitro|Nokia|Opera\ Mini|Palm|PlayStation\ Portable|portalmmm|Proxinet|ProxiNet|SHARP-TQ-GX10|SHG-i900|Small|SonyEricsson|Symbian\ OS|SymbianOS|TS21i-10|UP.Browser|UP.Link|webOS|Windows\ CE|WinWAP|YahooSeeker/M1A1-R2D2|iPhone|iPod|Android|BlackBerry9530|LG-TU915\ Obigo|LGE\ VX|webOS|Nokia5800).*
RewriteCond %{DOCUMENT_ROOT}/wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html -f
RewriteRule ^(.*) /wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
-----------------.htaccess-----------------
After you have enabled the plugin, look for the file "wp-content/cache/.htaccess". If it's not there you must create it. It should read:
# BEGIN supercache
<IfModule mod_mime.c>
<FilesMatch "\.html\.gz$">
ForceType text/html
FileETag None
</FilesMatch>
AddEncoding gzip .gz
AddType text/html .gz
</IfModule>
<IfModule mod_deflate.c>
SetEnvIfNoCase Request_URI \.gz$ no-gzip
</IfModule>
<IfModule mod_headers.c>
Header set Cache-Control 'max-age=3, must-revalidate'
</IfModule>
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType text/html A3
</IfModule>
``
# END supercache
Apache must be configured to allow the modules above. If you receive a "500 internal error" when serving requests to anonymous users you need to dig into your Apache configuration. This configuration in my virtual host works for me:
<Directory /home/www/>
AllowOverride All
</Directory>
Enable debugging in the plugin settings page and load the log file in a new browser tab. Then view your blog while logged in and logged out. You should see activity in the log. View the source of any page on your site. When a page is first created, you'll see the text "Dynamic page generated in XXXX seconds." and "Cached page generated by WP-Super-Cache on YYYY-MM-DD HH:MM:SS" at the end of the source code. On reload, a cached page will show the same timestamp so wait a few seconds before checking. In legacy caching mode, if you have compression enabled, the text "Compression = gzip" will be added. If compression is disabled and the page is served as a static html file, the text "super cache" will be added. The only other way to check if your cached file was served by PHP script or from the static cache is by looking at the HTTP headers. PHP cached pages will have the header "WP-Super-Cache: Served supercache file from PHP". Legacy cached files will have the header, "WP-Super-Cache: Served legacy cache file". I used the Live HTTP Headers extension for Firefox to examine the headers. You should also check your cache directory in wp-content/cache/supercache/hostname/ for static cache files. If the plugin rules are missing from your .htaccess file, the plugin will attempt to serve the super cached page if it's found. The header "WP-Super-Cache: Served supercache file from PHP" if this happens.
WP-Cache files are stored in wp-content/cache/ (or on MU sites in a blogs sub directory) and are named wp-cache-XXXXXXXXXXXXXXXXX.html. Associated meta files are stored in a meta sub directory. Those files contain information about the cached file. These files are generated by the "legacy caching" code in the plugin. Supercache files are stored in wp-content/cache/supercache/HOSTNAME/ where HOSTNAME is your domain name. The files are stored in directories matching your site's permalink structure.
This plugin is based on the excellent WP-Cache plugin. Besides the caching WP-Cache did this plugin 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 html page in your browser and uploaded it to replace your homepage.
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.
No, it will do the opposite. 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.
There are 2 ways of doing this. You can use Javascript to draw the part of the page you want to keep dynamic. That's what Google Adsense and many widgets from external sites do. Or you can use a WP Super Cache tag to do the job but you can't use mod_rewrite mode caching. You have to switch to PHP or legacy caching.
There are a few ways to do this, you can have functions that stay dynamic or you can include other files on every page load. To execute PHP code on every page load you can use either the "dynamic-cached-content", "mfunc", or "mclude" tags. The "dynamic-cached-content" tag is easier to use but the other tags can still be used. Make sure you duplicate the PHP code when using these tags. The first code is executed when the page is cached, while the second chunk of code is executed when the cached page is served to the next visitor. To execute WordPress functions you must define $wp_super_cache_late_init in your config file.
This code will include the file adverts.php and will execute the functions "print_sidebar_ad()" and "do_more_stuff()". Make sure there's no space before or after the PHP tags.
<!--dynamic-cached-content--><?php
include_once( ABSPATH . '/scripts/adverts.php' );
print_sidebar_ad();
do_more_stuff();
?><!--
include_once( ABSPATH . '/scripts/adverts.php' );
print_sidebar_ad();
do_more_stuff();
--><!--/dynamic-cached-content-->
To execute the function "function_name()":
<!--mfunc function_name( 'parameter', 'another_parameter' ) -->
<?php function_name( 'parameter', 'another_parameter' ) ?>
<!--/mfunc-->
To include another file:
<!--mclude file.php-->
<?php include_once( ABSPATH . 'file.php' ); ?>
<!--/mclude-->
That will include file.php under the ABSPATH directory, which is the same as where your wp-config.php file is located.
Example:
<!--mfunc date( 'Y-m-d H:i:s' ) -->
<?php date( 'Y-m-d H:i:s' ) ?>
<!--/mfunc-->
See the next qestion, you have to load WordPress before the cached file is served.
Cached files are served before almost all of WordPress is loaded. While that's great for performance it's a pain when you want to extend the plugin using a core part of WordPress. Set $wp_super_cache_late_init to "1" in wp-content/wp-cache-config.php and cached files will be served when "init" fires. WordPress and it's plugins will be loaded now. This is very useful when you are using the mfunc tag in your theme.
This plugin caches entire pages but some plugins think they can run PHP code every time a page loads. To fix this, the plugin needs to use Javascript/AJAX methods or the dynamic-cached-content/mfunc/mclude code described in the previous answer to update or display dynamic information.
When a visitor leaves a comment the cached file for that page is deleted and the next visitor recreates the cached page. A page takes time to load so what happens if it receives 100 visitors during this time? There won't be a cached page so WordPress will serve a fresh page for each user and the plugin will try to create a cached page for each of those 100 visitors causing a huge load on your server. This feature stops this happening. The cached page is not cleared when a comment is left. It is marked for rebuilding instead. The next visitor will regenerate the cached page while the old page is served to the other 99 visitors. The page is eventually loaded by the first visitor and the cached page updated. See this post for more.
Those bots usually only visit each page once and if the page is not popular there's no point creating a cache file that will sit idle on your server. However if you're not using legacy caching you can allow these visits to be cached by removing the list of bots from "Rejected User Agents" on the Advanced settings page.
A tiny proportion of websites will have problems with the following configuration:
Sometimes a category page is cached as the homepage of the site instead of the static page. I can't replicate the problem but a simple solution is to switch the plugin to PHP mode. For normal traffic you will see no difference in the speed of your site. You can also enable "Extra homepage checks" on the Advanced Settings page.
"Your blog doesn't support client caching (no 304 response to If-modified-since)." "Your feed doesn't support caching (no 304 response to If-modified-since)"
Supercache doesn't support 304 header checks in mod_rewrite mode but does support it in PHP mode. This is caching done by your browser, not the server. It is a check your browser does to ask the server if an updated version of the current page is available. If not, it doesn't download the old version again. The page is still cached by your server, just not by your visitors' browsers. Try the Cacheability Engine at http://www.ircache.net/cgi-bin/cacheability.py or http://redbot.org/ for further analysis.
That tracking adds a query string to each url linked from various sources like Twitter and feedreaders. Unfortunately it stops pages being supercached. See Joost's comment here for how to turn it into an anchor tag which can be supercached.
It's not good when the web server can write to these directories but sometimes shared hosting accounts are set up in this way to make administration easier. Use chmod 755 directory to fix the permissions or find the permissions section of your ftp client. This Google search will lead you to more information on this topic and there's also this codex page too. Unfortunately some hosts require that those directories be writable. If that's the case just ignore this warning.
Load your desktop ftp client and connect to your site. Navigate to the root (or the directory below it) of your site where you'll find wp-config.php. Download that file and edit it in a text editor. Delete the line define( 'WP_CACHE', true ); and save the file. Now upload it, overwriting the wp-config.php on your server.
Load your desktop ftp client and connect to your site. You may need to enable "Show hidden files" in the preferences of the ftp client. Navigate to the root of your site where you'll find the .htaccess file. Download that file and edit it in a text editor. Delete the lines between "# BEGIN WPSuperCache" and "# END WPSuperCache" and save the file. Now upload it, overwriting the .htaccess file on your server.
This page on the WordPress Codex explains everything you need to know about file permissions on your server and various ways of changing them.
You may have the "clear all cached files when new posts are made" option set. Clearing those files can take time plus your visitors will now be visiting uncached pages. Are you using Google Analytics campaign tracking with utm_source in the url? Those pages aren't cached. See the question, "How should I best use the utm_source tracking tools in Google Analytics with this plugin" above for how to use them properly. Cached pages have to be refreshed when posts are made. Perhaps your server just isn't up to the job of serving the amount of traffic you get. Enable the "cache rebuild" feature as that may help.
The only real limit are limits defined by your server. For example, EXT2 and EXT3 allow a maximum of 31,999 sub directories so if you have a flat permalink structure (like /%POSTNAME%/) and more than 32,000 posts you may run into problems. Likewise, if you run a multisite network and have more than 31,999 sites (blogs) you won't be able to cache all of them. Realistically if you had that many active sites you wouldn't be running on one server.
You'll have to use a separate mobile plugin to render a page formatted for those visitors. The following plugins have been tested but YMMV depending on mobile client. * [WPTouch] (http://wordpress.org/extend/plugins/wptouch/) * [WordPress Mobile Edition] (http://wordpress.org/extend/plugins/wordpress-mobile-edition/) * [WordPress Mobile Pack] (http://wordpress.org/extend/plugins/wordpress-mobile-pack/) (can't have "Don't cache pages for known users." enabled)
If things don't work when you installed the plugin here are a few things to check:
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 );
Garbage collection of old cache files won't work if WordPress can't find wp-cron.php. If your hostname resolves to 127.0.0.1 it could be preventing the garbage collection from working. Check your access_logs for wp-cron.php entries. Do they return a 404 (file not found) or 200 code? If it's 404 or you don't see wp-cron.php anywhere WordPress may be looking for that script in the wrong place. You should speak to your server administator to correct this or edit /etc/hosts on Unix servers and remove the following line. Your hostname must resolve to the external IP address other servers on the network/Internet use. See http://yoast.com/wp-cron-issues/ for more.
127.0.0.1 myhostname.com
A line like "127.0.0.1 localhost localhost.localdomain" is ok.
If supercache cache files are generated but not served, check the permissions on all your wp-content/cache/supercache folders (and each of wp-content cache and supercache folders) and wp-content/cache/.htaccess. If your PHP runs as a different user to Apache and permissions are strict Apache may not be able to read the PHP generated cache files. To fix you must add the following line to your wp-config.php (Add it above the WP_CACHE define.) Then clear your cache.
umask( 0022 );
If you see garbage in your browser after enabling compression in the plugin, compression may already be enabled in your web server. In Apache you must disable mod_deflate, or in PHP zlib compression may be enabled. You can disable that in three ways. If you have root access, edit your php.ini and find the zlib.output_compression setting and make sure it's "Off" or add this line to your .htaccess:
php_flag zlib.output_compression off
If that doesn't work, add this line to your wp-config.php:
`ini_set('zlib.output_compression', 0);`
22. The "white screen of death" or a blank page when you visit your site is almost always caused by a PHP error but it may also be caused by APC. Disable that PHP extension if you have trouble and replace with eAccelerator or Xcache. 23. After uninstalling, your permalinks may break if you remove the WordPress mod_rewrite rules too. Regenerate those rules by visiting the Settings->Permalink page and saving that form again. 24. If your blog refuses to load make sure your wp-config.php is correct. Are you missing an opening or closing PHP tag? 25. Your front page is ok but posts and pages give a 404? Go to Settings->permalinks and click "Save" once you've selected a custom permalink structure. You may need to manually update your .htaccess file. 26. If certain characters do not appear correctly on your website your server may not be configured correctly. You need to tell visitors what character set is used. Go to Settings->Reading and copy the 'Encoding for pages and feeds' value. Edit the .htaccess file with all your Supercache and WordPress rewrite rules and add this at the top, replacing CHARSET with the copied value. (for example, 'UTF-8')
`AddDefaultCharset CHARSET`