Pantheon Advanced Page Cache vs WP Super Cache

For sites wanting fine-grained control over how their responses are represented in their edge cache, Pantheon Advanced Page Cache is the golden ticket. Here’s a high-level overview of how the plugin works: When a response is generated, the plugin uses surrogate keys based on WordPress’ main WP_Query object to “tag” the response with identifers for the data used in the response. See the “Adding Custom Keys” section for including your own surrogate keys. When WordPress data is modified, the plugin triggers a purge request for the data’s corresponding surrogate keys. Because of its surrogate key technology, Pantheon Advanced Page Cache empowers WordPress sites with a significantly more accurate cache purge mechanism, and generally higher cache hit rate. It even works with the WordPress REST API. Go forth and make awesome! And, once you’ve built something great, send us feature requests (or bug reports). How It Works Pantheon Advanced Page Cache makes heavy use of surrogate keys, which enable responses to be “tagged” with identifiers that can then later be used in purge requests. For instance, a home page response might include the Surrogate-Key header with these keys: Surrogate-Key: front home post-43 user-4 post-41 post-9 post-7 post-1 user-1 Similarly, a GET requests to /wp-json/wp/v2/posts might include the Surrogate-Key header with these keys: Surrogate-Key: rest-post-collection rest-post-43 rest-post-43 rest-post-9 rest-post-7 rest-post-1 Because cached responses include metadata describing the data therein, surrogate keys enable more flexible purging behavior like: When a post is updated, clear the cache for the post’s URL, the homepage, any index view the post appears on, and any REST API endpoints the post is present in. When an author changes their name, clear the cache for the author’s archive and any post they’ve authored. There is a limit to the number of surrogate keys in a response, so we’ve optimized them based on a user’s expectation of a normal WordPress site. See the “Emitted Keys” section for full details on which keys are included, and the “Adding Custom Keys” section following for information on how to add your own. Adding Custom Keys By default, Pantheon Advanced Page Cache generates surrogate keys based on an interpretation of the main WP_Query query object. Because WordPress sends headers before the page is rendered, you need to use the pantheon_wp_main_query_surrogate_keys filter to include additional surrogate keys for any data present on the page. For example, to include surrogate keys for a sidebar rendered on the homepage, you can filter the keys using the is_home() template tag: /** * Add surrogate key for the featured content sidebar rendered on the homepage. */ add_filter( 'pantheon_wp_main_query_surrogate_keys', function( $keys ){ if ( is_home() ) { $keys[] = 'sidebar-home-featured'; } return $keys; }); Then, when sidebars are updated, you can use the pantheon_wp_clear_edge_keys() helper function to emit a purge event specific to the surrogate key: /** * Trigger a purge event for the featured content sidebar when widgets are updated. */ add_action( 'update_option_sidebars_widgets', function() { pantheon_wp_clear_edge_keys( array( 'sidebar-home-featured' ) ); }); Similarly, to include surrogate keys for posts queried on the homepage, you can pre-fetch the posts before the page is rendered: /** * An example of pre-fetching a WP_Query to tag the * response with queried data. You'd use `papcx_wp_query()` * a second time within your template to use the data. */ add_filter( 'pantheon_wp_main_query_surrogate_keys', function( $keys ) { if ( is_home() ) { $query = papcx_wp_query( array( 'post_type' => 'page', ) ); foreach( $query->posts as $post ) { $keys[] = 'post-' . $post->ID; } } return $keys; }); /** * Register a 'papc-non-persistent' cache group to cache data * in a non-persistent manner. We only want data in this group * to be cached within the page request. */ add_action( 'init', function(){ wp_cache_add_non_persistent_groups( array( 'papc-non-persistent' ) ); }); /** * Helper function to instantiate a WP_Query object only * once per page request. * * @param array $args Arguments to pass to WP_Query. * @return WP_Query */ function papcx_wp_query( $args = array() ) { $cache_key = md5( serialize( $args ) ); // WP_Query object will be in cache the second time we use the function. $cache_value = wp_cache_get( $cache_key, 'papc-non-persistent' ); if ( false !== $cache_value ) { return $cache_value; } $query = new WP_Query( $args ); wp_cache_set( $cache_key, $query, 'papc-non-persistent' ); return $query; } Because Pantheon Advanced Page Cache already handles WordPress post purge events, there’s no additional call to pantheon_wp_clear_edge_keys(). Lastly, the pantheon_wp_rest_api_surrogate_keys filter lets you filter surrogate keys present in a REST API response. Additional purging by path When a post is published for the first time, the permalink’s path is also purged even if it has no matching keys. This can be further filtered with the pantheon_clear_post_path filter. add_action('pantheon_clear_post_path', function($paths) { // Add or remove paths from $paths return $paths }, 10, 3); Need a bit more power? In addition to pantheon_wp_clear_edge_keys(), there are two additional helper functions you can use: pantheon_wp_clear_edge_paths( $paths = array() ) – Purge cache for one or more paths. pantheon_wp_clear_edge_all() – Warning! With great power comes great responsibility. Purge the entire cache, but do so wisely. Ignoring Specific Post Types By default, Pantheon Advanced Page Cache is pretty aggressive in how it clears its surrogate keys. Specifically, any time wp_insert_post is called (which can include any time a post of any type is added or updated, even private post types), it will purge a variety of keys including home, front, 404 and feed. To bypass or override this behavior, since 1.5.0 we have a filter allowing an array of post types to ignore to be passed before those caches are purged. By default, the revision post type is ignored, but others can be added: /** * Add a custom post type to the ignored post types. * * @param array $ignored_post_types The array of ignored post types. * @return array */ function filter_ignored_posts( $ignored_post_types ) { $ignored_post_types[] = 'my-post-type'; // Ignore my-post-type from cache purges. return $ignored_post_types; } add_filter( 'pantheon_purge_post_type_ignored', 'filter_ignored_posts' ); This will prevent the cache from being purged if the given post type is updated. Setting the Cache Max Age with a filter The cache max age setting is controlled by the Pantheon Page Cache admin page. As of 2.0.0, there are three cache age options by default — 1 week, 1 month, 1 year. Pantheon Advanced Page Cache automatically purges the cache of updated and related posts and pages, but you might want to override the cache max age value and set it programmatically. In this case, you can use the pantheon_cache_default_max_age filter added in Pantheon MU plugin 1.4.0+. For example: add_filter( 'pantheon_cache_default_max_age', function() { return 10 * DAY_IN_SECONDS; } ); When the cache max age is filtered in this way, the admin option is disabled and a notice is displayed. Updating the cache max age based on nonces Nonces created on the front-end, often used to secure forms and other data, have a lifetime, and if the cache max age is longer than the nonce lifetime, the nonce may expire before the cache does. To avoid this, you can use the pantheon_cache_nonce_lifetime action to set the pantheon_cache_default_max_age to less than the nonce lifetime. For example: do_action( 'pantheon_cache_nonce_lifetime' ); It’s important to wrap your do_action in the appropriate conditionals to ensure that the action is only called when necessary and not filtering the cache max age in cases when it’s not necessary. This might mean only running on certain pages or in certain contexts in your code. WP-CLI Commands This plugin implements a variety of WP-CLI commands. All commands are grouped into the wp pantheon cache namespace. $ wp help pantheon cache NAME wp pantheon cache DESCRIPTION Manage the Pantheon Advanced Page Cache. SYNOPSIS wp pantheon cache SUBCOMMANDS purge-all Purge the entire page cache. purge-key Purge one or more surrogate keys from cache. purge-path Purge one or more paths from cache. Use wp help pantheon cache to learn more about each command. Debugging By default, Pantheon’s infrastructure strips out the Surrogate-Key response header before responses are served to clients. The contents of this header can be viewed as Surrogate-Key-Raw by adding on a debugging header to the request. A direct way of inspecting headers is with curl -I. This command will make a request and show just the response headers. Adding -H "Pantheon-Debug:1" will result in Surrogate-Key-Raw being included in the response headers. The complete command looks like this: curl -IH "Pantheon-Debug:1" https://scalewp.io/ Piping to grep will filter the output down to just the Surrogate-Key-Raw header: curl -IH "Pantheon-Debug:1" https://scalewp.io/ | grep -i Surrogate-Key-Raw Tada! Emitted Keys and Purge Events Emitted Keys on Traditional Views Home / Emits surrogate keys: home, front, post- (all posts in main query) Single post /2016/10/14/surrogate-keys/ Emits surrogate keys: single, post- , post-user- , post-term- (all terms assigned to post) Author archive /author/pantheon/ Emits surrogate keys: archive, user- , post- (all posts in main query) Term archive /tag/cdn/ Emits surrogate keys: archive, term- , post- (all posts in main query) Day archive /2016/10/14/ Emits surrogate keys: archive, date, post- (all posts in main query) Month archive /2016/10/ Emits surrogate keys: archive, date, post- (all posts in main query) Year archive /2016/ Emits surrogate keys: archive, date, post- (all posts in main query) Search /?s= Emits surrogate keys: search, either search-results or search-no-results, post- (all posts in main query) Not found (404) Emits surrogate keys: 404 Emitted Keys on REST API Endpoints Posts /wp-json/wp/v2/posts emits surrogate keys: rest-post-collection, rest-post- /wp-json/wp/v2/posts/ emits surrogate keys: rest-post- Pages /wp-json/wp/v2/pages emits surrogate keys: rest-page-collection, rest-post- /wp-json/wp/v2/pages/ emits surrogate keys: rest-post- Categories /wp-json/wp/v2/categories emits surrogate keys: rest-category-collection, rest-term- /wp-json/wp/v2/categories/ emits surrogate keys: rest-term- Tags /wp-json/wp/v2/tags emits surrogate keys: rest-post_tag-collection, rest-term- /wp-json/wp/v2/tags/ emits surrogate keys: rest-term- Comments /wp-json/wp/v2/comments emits surrogate keys: rest-comment-collection, rest-comment-post- , rest-comment- /wp-json/wp/v2/comments/ emits surrogate keys: rest-comment-post- , rest-comment- Users /wp-json/wp/v2/users emits surrogate keys: rest-user-collection, rest-user- /wp-json/wp/v2/users/ emits surrogate keys: rest-user- Settings /wp-json/wp/v2/settings emits surrogate keys: rest-setting- Purge Events Different WordPress actions cause different surrogate keys to be purged, documented here. wp_insert_post / transition_post_status / before_delete_post / delete_attachment Purges surrogate keys: home, front, 404, post- , user- , term- , rest- -collection, rest-comment-post- Affected views: homepage, single post, any page with 404 header, any archive where post displays, author archive, term archive, REST API collection and resource endpoints clean_post_cache Purges surrogate keys: post- , rest-post- Affected views: single post, REST API resource endpoint created_term / edited_term / delete_term Purges surrogate keys: term- , post-term- , rest- -collection Affected views: term archive, any post where the term is assigned, REST API collection and resource endpoints clean_term_cache Purges surrogate keys: term- , rest-term- Affected views: term archive, REST API resource endpoint wp_insert_comment / transition_comment_status Purges surrogate keys: rest-comment-collection, rest-comment- Affected views: REST API collection and resource endpoints clean_comment_cache Purges surrogate keys: rest-comment- Affected views: REST API resource endpoint clean_user_cache Purges surrogate keys: user- , rest-user- Affected views: author archive, any post where the user is the author updated_option Purges surrogate keys: rest-setting- Affected views: REST API resource endpoint Surrogate Keys for taxonomy terms Setting surrogate keys for posts with large numbers of taxonomies (such as WooCommerce products with a large number of global attributes) can suffer from slower queries. Surrogate keys can be skipped for ‘product’ post types’ taxonomy terms (or any other criteria you see fit) with the following filter: function custom_should_add_terms($should_add_terms, $wp_query) { if ( $wp_query->is_singular( 'product' ) ) { return false; } return $should_add_terms; } add_filter('pantheon_should_add_terms', 'custom_should_add_terms', 10, 2); Other Filters pantheon_apc_disable_admin_notices Since 2.0.0, Pantheon Advanced Page Cache displays a number of admin notices about your current cache max age value. You can disable these notices with the pantheon_apc_disable_admin_notices filter. add_filter( 'pantheon_apc_disable_admin_notices', '__return_true' ); Alternately, the function callback is passed into the pantheon_apc_disable_admin_notices filter, allowing you to specify precisely which notice to disable, for example: add_filter( 'pantheon_apc_disable_admin_notices', function( $disable_notices, $callback ) { if ( $callback === '\\Pantheon_Advanced_Page_Cache\\Admin_Interface\\admin_notice_maybe_recommend_higher_max_age' ) { return true; } return $disable_notices; }, 10, 2 ); The above example would disable only the admin notice recommending a higher cache max age. Plugin Integrations Pantheon Advanced Page Cache integrates with WordPress plugins, including: WPGraphQL Contributing See CONTRIBUTING.md for information on contributing.

This plugin generates static html files from your dynamic WordPress blog. After a html file is generated your webserver will serve that file instead of processing the comparatively heavier and more expensive WordPress PHP scripts. The static html files will be served to the vast majority of your users: Users who are not logged in. Users who have not left a comment on your blog. Or users who have not viewed a password protected post. 99% of your visitors will be served static html files. One cached file can be served thousands of times. Other visitors will be served custom cached files tailored to their visit. If they are logged in, or have left comments those details will be displayed and cached for them. The plugin serves cached files in 3 ways (ranked by speed): Expert. The fastest method is by using Apache mod_rewrite (or whatever similar module your web server supports) to serve “supercached” static html files. This completely bypasses PHP and is extremely quick. If your server is hit by a deluge of traffic it is more likely to cope as the requests are “lighter”. This does require the Apache mod_rewrite module (which is probably installed if you have custom permalinks) and a modification of your .htaccess file which is risky and may take down your site if modified incorrectly. Simple. Supercached static files can be served by PHP and this is the recommended way of using the plugin. The plugin will serve a “supercached” file if it exists and it’s almost as fast as the mod_rewrite method. It’s easier to configure as the .htaccess file doesn’t need to be changed. You still need a custom permalink. You can keep portions of your page dynamic in this caching mode. WP-Cache caching. This is mainly used to cache pages for known users, URLs with parameters and feeds. Known users are logged in users, visitors who leave comments or those who should be shown custom per-user data. It’s the most flexible caching method and slightly slower. WP-Cache caching will also cache visits by unknown users if supercaching is disabled. You can have dynamic parts to your page in this mode too. This mode is always enabled but you can disable caching for known users, URLs with parameters, or feeds separately. Set the constant “DISABLE_SUPERCACHE” to 1 in your wp-config.php if you want to only use WP-Cache caching. If you’re not comfortable with editing PHP files then use simple mode. It’s easy to set up and very fast. Recommended Settings Simple caching. Compress pages. Don’t cache pages for known users. Cache rebuild. CDN support. Extra homepage checks. Garbage collection is the act of cleaning up cache files that are out of date and stale. There’s no correct value for the expiry time but a good starting point is 1800 seconds. Consider deleting the contents of the “Rejected User Agents” text box and allow search engines to cache files for you. Preload as many posts as you can and enable “Preload Mode”. Garbage collection of old cached files will be disabled. If you don’t care about sidebar widgets updating often set the preload interval to 2880 minutes (2 days) so all your posts aren’t recached very often. When the preload occurs the cache files for the post being refreshed is deleted and then regenerated. Afterwards a garbage collection of all old files is performed to clean out stale cache files. Even with preload mode enabled cached files will still be deleted when posts are modified or comments made. Development Active development of this plugin is handled on GitHub. Translation of the plugin into different languages is on the translation page. Documentation If you need more information than the following, you can have a look at the wiki or the Developer documentation. Preloading You can generate cached files for the posts, categories and tags of your site by preloading. Preloading will visit each page of your site generating a cached page as it goes along, just like any other visitor to the site. Due to the sequential nature of this function, it can take some time to preload a complete site if there are many posts. To make preloading more effective it can be useful to disable garbage collection so that older cache files are not deleted. This is done by enabling “Preload Mode” in the settings. Be aware however, that pages will go out of date eventually but that updates by submitting comments or editing posts will clear portions of the cache. Garbage Collection Your cache directory fills up over time, which takes up space on your server. If space is limited or billed by capacity, or if you worry that the cached pages of your site will go stale then garbage collection has to be done. Garbage collection happens on a regular basis and deletes old files in the cache directory. On the advanced settings page you can specify: 1. Cache timeout. How long cache files are considered fresh for. After this time they are stale and can be deleted. 2. Scheduler. Setup how often garbage collection should be done. 3. Notification emails. You can be informed on garbage collection job progress. There’s no right or wrong settings for garbage collection. It depends on your own site. If your site gets regular updates, or comments then set the timeout to 1800 seconds, and set the timer to 600 seconds. If your site is mostly static you can disable garbage collection by entering 0 as the timeout, or use a really large timeout value. The cache directory, usually wp-content/cache/ is only for temporary files. Do not ever put important files or symlinks to important files or directories in that directory. They will be deleted if the plugin has write access to them. CDN A Content Delivery Network (CDN) is usually a network of computers situated around the world that will serve the content of your website faster by using servers close to you. Static files like images, Javascript and CSS files can be served through these networks to speed up how fast your site loads. You can also create a “poor man’s CDN” by using a sub domain of your domain to serve static files too. OSSDL CDN off-linker has been integrated into WP Super Cache to provide basic CDN support. It works by rewriting the URLs of files (excluding .php files) in wp-content and wp-includes on your server so they point at a different hostname. Many CDNs support origin pull. This means the CDN will download the file automatically from your server when it’s first requested, and will continue to serve it for a configurable length of time before downloading it again from your server. Configure this on the “CDN” tab of the plugin settings page. This is an advanced technique and requires a basic understanding of how your webserver or CDNs work. Please be sure to clear the file cache after you configure the CDN. REST API There are now REST API endpoints for accessing the settings of this plugin. You’ll need to be authenticated as an admin user with permission to view the settings page to use it. This has not been documented yet but you can find all the code that deals with this in the “rest” directory. Custom Caching It is now possible to hook into the caching process using the add_cacheaction() function. Three hooks are available: ‘wp_cache_get_cookies_values’ – modify the key used by WP Cache. ‘add_cacheaction’ – runs in phase2. Allows a plugin to add WordPress hooks. ‘cache_admin_page’ – runs in the admin page. Use it to modify that page, perhaps by adding new configuration options. There is one regular WordPress filter too. Use the “do_createsupercache” filter to customize the checks made before caching. The filter accepts one parameter. The output of WP-Cache’s wp_cache_get_cookies_values() function. WP Super Cache has its own plugin system, loaded before most of WordPress. Add your own plugin either by putting it in the wp-content/plugins/wp-super-cache-plugins directory, or by calling wpsc_add_plugin( $name ) with the full path to the plugin. The cookies used to identify “known users” can be modified with wpsc_add_cookie( $name ) and wpsc_delete_cookie( $name ). See plugins/searchengine.php as an example. Troubleshooting If things don’t work when you installed the plugin here are a few things to check: Is wp-content writable by the web server? Is there a wp-content/wp-cache-config.php ? If not, copy the file wp-super-cache/wp-cache-config-sample.php to wp-content/wp-cache-config.php and make sure WPCACHEHOME points at the right place. Is there a wp-content/advanced-cache.php ? If not, then you must copy wp-super-cache/advanced-cache.php into wp-content/. You must edit the file and change the path so it points at the wp-super-cache folder. If pages are not cached at all, remove wp-content/advanced-cache.php and recreate it, following the advice above. Make sure the following line is in wp-config.php and it is ABOVE the “require_once(ABSPATH.’wp-settings.php’);” line: define( 'WP_CACHE', true ); Try the Settings->WP Super Cache page again and enable cache. Look in wp-content/cache/supercache/. Are there directories and files there? Anything in your php error_log? If your browser keeps asking you to save the file after the super cache is installed you must disable Super Cache compression. Go to the Settings->WP Super Cache page and disable it there. File locking errors such as “failed to acquire key 0x152b: Permission denied in…” or “Page not cached by WP Super Cache. Could not get mutex lock.” are a sign that you may have to use file locking. Edit wp-content/wp-cache-config.php and uncomment “$use_flock = true” or set $sem_id to a different value. You can also disable file locking from the Admin screen as a last resort. Make sure cache/wp_cache_mutex.lock is writable by the web server if using coarse file locking. The cache folder cannot be put on an NFS or Samba or NAS share. It has to be on a local disk. File locking and deleting expired files will not work properly unless the cache folder is on the local machine. Garbage collection of old cache files won’t work if WordPress can’t find wp-cron.php. Check your access_logs for wp-cron.php entries and that your hostname resolves to the external IP address other servers on the network/Internet use. If old pages are being served to your visitors via the supercache, you may be missing Apache modules (or their equivalents if you don’t use Apache). 3 modules are required: mod_mime, mod_headers and mod_expires. The last two are especially important for making sure browsers load new versions of existing pages on your site. The error message, “WP Super Cache is installed but broken. The path to wp-cache-phase1.php in wp-content/advanced-cache.php must be fixed!” appears at the end of every page. Open the file wp-content/advanced-cache.php in your favourite editor. Is the path to wp-cache-phase1.php correct? This file will normally be in wp-content/plugins/wp-super-cache/. If it is not correct the caching engine will not load. Caching doesn’t work. The timestamp on my blog keeps changing when I reload. Check that the path in your .htaccess rules matches where the supercache directory is. You may have to hardcode it. Try disabling supercache mode. 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); 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. If your blog refuses to load make sure your wp-config.php is correct. Are you missing an opening or closing PHP tag? 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. 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 The error message, “WP Super Cache is installed but broken. The constant WPCACHEHOME must be set in the file wp-config.php and point at the WP Super Cache plugin directory.” appears at the end of every page. You can delete wp-content/advanced-cache.php and reload the plugin settings page or edit wp-config.php and look for WPCACHEHOME and make sure it points at the wp-super-cache folder. This will normally be wp-content/plugins/wp-super-cache/ but you’ll likely need the full path to that file (so it’s easier to let the settings page fix it). If it is not correct the caching engine will not load. If your server is running into trouble because of the number of semaphores used by the plugin it’s because your users are using file locking which is not recommended (but is needed by a small number of users). You can globally disable file locking by defining the constant WPSC_DISABLE_LOCKING, or defining the constant WPSC_REMOVE_SEMAPHORE so that sem_remove() is called after every page is cached but that seems to cause problems for other processes requesting the same semaphore. Best to disable it. Set the variable $htaccess_path in wp-config.php or wp-cache-config.php to the path of your global .htaccess if the plugin is looking for that file in the wrong directory. This might happen if you have WordPress installed in an unusual way.