Title: Memcached Object Cache Author: Mark Jaquith Published: December 19, 2005 Last modified: November 8, 2022 --- Search plugins This plugin **hasn’t been tested with the latest 3 major releases of WordPress**. It may no longer be maintained or supported and may have compatibility issues when used with more recent versions of WordPress. ![](https://s.w.org/plugins/geopattern-icon/memcached.svg) # Memcached Object Cache By [Mark Jaquith](https://profiles.wordpress.org/markjaquith/) [Download](https://downloads.wordpress.org/plugin/memcached.4.0.0.zip) * [Details](https://pcd.wordpress.org/plugins/memcached/#description) * [Reviews](https://pcd.wordpress.org/plugins/memcached/#reviews) * [Installation](https://pcd.wordpress.org/plugins/memcached/#installation) * [Development](https://pcd.wordpress.org/plugins/memcached/#developers) [Support](https://wordpress.org/support/plugin/memcached/) ## Description Memcached Object Cache provides a persistent backend for the WordPress object cache. A memcached server and the PECL memcache extension are required. ## Installation 1. Install [memcached](http://danga.com/memcached) on at least one server. Note the connection info. The default is `127.0.0.1:11211`. 2. Install the [PECL memcache extension](http://pecl.php.net/package/memcache) 3. Copy object-cache.php to wp-content 4. Add the `WP_CACHE_KEY_SALT` constant to the `wp-config.php`: 5. `php define( 'WP_CACHE_KEY_SALT', '...long random string...' ); This helps prevent cache pollution when multiplte WordPress installs are using the same Memcached server. The value must be unique for each WordPress install. ## FAQ ### How can I manually specify the memcached server(s)? Add something similar to the following to wp-config.php above `/* That's all, stop editing! Happy blogging. */`: ``` $memcached_servers = array( 'default' => array( '10.10.10.20:11211', '10.10.10.30:11211' ) ); ``` The top level array keys, are cache groups, where ‘default’ corresponds to any cache group that is not explicitly defined. This allows for specifying memcached servers that only handle certain cache groups. The most common use is only specifying ‘default’. Possible cache groups are: ``` {$taxonomy}_relationships {$meta_type}_meta {$taxonomy}_relationships blog-details blog-id-cache blog-lookup bookmark calendar category comment counts general global-posts options plugins post_ancestors post_meta posts rss site-lookup site-options site-transient terms themes timeinfo transient user_meta useremail userlogins usermeta users userslugs widget ``` ## Reviews ![](https://secure.gravatar.com/avatar/9610e77b9c1acfe8436ce0afe252d9536b6b4b4f23aa97a10ebc24cba9bbd76f? s=60&d=retro&r=g) ### 󠀁[Amazing performance improvement!](https://wordpress.org/support/topic/amazing-performance-improvement/)󠁿 [rambillo](https://profiles.wordpress.org/rambillo/) October 21, 2023 Install is not like other plugins — and in fact if you do upload it to plugins and then activate it, it’ll bring your site down in many cases. You can upload it (but don’t activate!) and then use the server side to move the plugin file manually into wp-content (and then delete the uploaded plugin folder and readme.txt). But that’s not enough to make the whole thing work! You also need memcached running on your server and properly configured, and the pecl memcache extension compiled on the server side in your php configuration, too. Make sure to use a unique salt as well. Once it’s all there, the speed improvement is significant! Happy to try and help those that respond to this thread if you need — or at least try to get you pointed in the right direction. Thanks for the plugin, devs! Appreciate as you update and keep current as well! ![](https://secure.gravatar.com/avatar/a15ec539baae35aa862ff604b11ba327a6a990d0ff7372d55314217f7099ab5f? s=60&d=retro&r=g) ### 󠀁[Can t install the plugin](https://wordpress.org/support/topic/can-t-install-the-plugin/)󠁿 [kalagan80](https://profiles.wordpress.org/kalagan80/) September 4, 2023 Unable to install the plugin : application not recognized. ![](https://secure.gravatar.com/avatar/ee94e283f9e6a17442a8670a40c2ffb025339b527d26d76f75d4d54ec3232ea8? s=60&d=retro&r=g) ### 󠀁[@terrykernan I get critical error when moving](https://wordpress.org/support/topic/terrykernan-i-get-critical-error-when-moving/)󠁿 [markleeuw](https://profiles.wordpress.org/markleeuw/) July 8, 2023 @terrykernan I moved like you said but then i get ciritcal error and can enter the Admin section of wordpress, when i remove it from WP-Content everything works again. I installed the plugin only because i have Redis on my host ![](https://secure.gravatar.com/avatar/fb5ab2d835f31b7bac4b4df4d061d4bf782071e55329e792b2e0ef25c61da290? s=60&d=retro&r=g) ### 󠀁[Cannot redeclare wp_cache_add](https://wordpress.org/support/topic/cannot-redeclare-wp_cache_add-4/)󠁿 [terrykernan](https://profiles.wordpress.org/terrykernan/) May 17, 2023 1 reply Tip for others here, if you are getting this error: “Cannot redeclare wp_cache_add” It probably means you have the object-cache.php file in the wrong directory, it should not be in the plugins/memcached/ folder, it should be moved to the wp-content folder! ![](https://secure.gravatar.com/avatar/374ea40afb714496967ecdd047f26a4c48c9b2b6acac65646e08bf27b7ad8806? s=60&d=retro&r=g) ### 󠀁[FATAL ERROR PHP](https://wordpress.org/support/topic/fatal-error-php-9/)󠁿 [legarsfred](https://profiles.wordpress.org/legarsfred/) April 5, 2023 1 reply Fatal error: Cannot redeclare wp_cache_add() (previously declared in /htdocs/wp- includes/cache.php:41) in /htdocs/wp-content/plugins/memcached/object-cache.php on line 19 ![](https://secure.gravatar.com/avatar/93083231f4567aaebde042533a0a3b62f0a7da89cf857125fa58a5c7f71f665d? s=60&d=retro&r=g) ### 󠀁[Works great!](https://wordpress.org/support/topic/works-great-8687/)󠁿 [Miguel](https://profiles.wordpress.org/miguelgilmartinez/) February 16, 2023 It works well even with WPRocket Cache plugin. If you get fatal errors don’t forget to install PECL memcache module to PHP. [ Read all 30 reviews ](https://wordpress.org/support/plugin/memcached/reviews/) ## Contributors & Developers “Memcached Object Cache” is open source software. The following people have contributed to this plugin. Contributors * [ Mark Jaquith ](https://profiles.wordpress.org/markjaquith/) * [ Ryan Boren ](https://profiles.wordpress.org/ryan/) * [ Matt Martz ](https://profiles.wordpress.org/sivel/) * [ Andy Skelton ](https://profiles.wordpress.org/andy/) * [ Andrew Nacin ](https://profiles.wordpress.org/nacin/) * [ Barry ](https://profiles.wordpress.org/barry/) * [ Erick Hitter ](https://profiles.wordpress.org/ethitter/) * [ nickdaugherty ](https://profiles.wordpress.org/nickdaugherty/) * [ Mohammad Jangda ](https://profiles.wordpress.org/batmoo/) * [ Simon Wheatley ](https://profiles.wordpress.org/simonwheatley/) * [ jenkoian ](https://profiles.wordpress.org/jenkoian/) * [ Boro Sitnikovski ](https://profiles.wordpress.org/bor0/) * [ Andrija Vučinić ](https://profiles.wordpress.org/aidvu/) “Memcached Object Cache” has been translated into 6 locales. Thank you to [the translators](https://translate.wordpress.org/projects/wp-plugins/memcached/contributors) for their contributions. [Translate “Memcached Object Cache” into your language.](https://translate.wordpress.org/projects/wp-plugins/memcached) ### Interested in development? [Browse the code](https://plugins.trac.wordpress.org/browser/memcached/), check out the [SVN repository](https://plugins.svn.wordpress.org/memcached/), or subscribe to the [development log](https://plugins.trac.wordpress.org/log/memcached/) by [RSS](https://plugins.trac.wordpress.org/log/memcached/?limit=100&mode=stop_on_copy&format=rss). ## Changelog #### 4.0.0 * Add preemptive filter pre_wp_cache_get * Add flush_number replication to prevent accidental flush due to flush_number eviction, server rotation, etc. #### 3.2.2 * Remove filter, and base key stripping on presence of `key_salt` #### 3.2.1 * Fix bug allowing **slow-ops** entries to have the same key, so toggling doesn’t work #### 3.2.0 * Better stats(). Now shows cache group/individual calls with size of the payload and timings. * PHP 5.6.20 is now required * Fix **get_multi** to show per group calls * Added filter **(memcached_strip_keys)** to bypass memcached key stripping * Special group for **slow-ops** ( > 5ms ) with backtrace #### 3.1.0 * Add **wp_cache_get_multi** * Add support for the **$found** parameter * Set a variable for $max_expiration to 30 days * Code style changes * Different coloring for unknown stats group * Store host/port on failure_callback * Default stats counts #### 3.0.2 * Better output of HTML #### 3.0.1 * Fix key generation error in switch_to_blog() #### 3.0.0 * Flush site cache by rotating keys * Flush global cache when flushing main site #### 2.0.6 * Flush the local cache on wp_cache_flush() #### 2.0.5 * Fix missing global in switch_to_blog #### 2.0.4 * Remove deprecated constructor #### 2.0.3 * Support for unix sockets #### 2.0.2 * Break references by cloning objects * Keep local cache in sync with memcached when using incr and decr * Handle limited environments where is_multisite() is not defined * Fix setting and getting 0 * PHP 5.2.4 is now required * Use the WP_CACHE_KEY_SALT constant if available to guarantee uniqueness of keys ## Meta * Version **4.0.0** * Last updated **3 years ago** * Active installations **20+** * WordPress version ** 5.3 or higher ** * Tested up to **6.1.10** * PHP version ** 5.6.20 or higher ** * Languages * [Chinese (China)](https://cn.wordpress.org/plugins/memcached/), [Dutch (Belgium)](https://nl-be.wordpress.org/plugins/memcached/), [English (UK)](https://en-gb.wordpress.org/plugins/memcached/), [English (US)](https://wordpress.org/plugins/memcached/), [German](https://de.wordpress.org/plugins/memcached/), [Polish](https://pl.wordpress.org/plugins/memcached/), and [Russian](https://ru.wordpress.org/plugins/memcached/). * [Translate into your language](https://translate.wordpress.org/projects/wp-plugins/memcached) * Tags * [cache](https://pcd.wordpress.org/plugins/tags/cache/)[memcached](https://pcd.wordpress.org/plugins/tags/memcached/) * [Advanced View](https://pcd.wordpress.org/plugins/memcached/advanced/) ## Ratings 3.8 out of 5 stars. * [ 19 5-star reviews ](https://wordpress.org/support/plugin/memcached/reviews/?filter=5) * [ 1 4-star review ](https://wordpress.org/support/plugin/memcached/reviews/?filter=4) * [ 1 3-star review ](https://wordpress.org/support/plugin/memcached/reviews/?filter=3) * [ 0 2-star reviews ](https://wordpress.org/support/plugin/memcached/reviews/?filter=2) * [ 8 1-star reviews ](https://wordpress.org/support/plugin/memcached/reviews/?filter=1) [Add my review](https://wordpress.org/support/plugin/memcached/reviews/#new-post) [See all reviews](https://wordpress.org/support/plugin/memcached/reviews/) ## Contributors * [ Mark Jaquith ](https://profiles.wordpress.org/markjaquith/) * [ Ryan Boren ](https://profiles.wordpress.org/ryan/) * [ Matt Martz ](https://profiles.wordpress.org/sivel/) * [ Andy Skelton ](https://profiles.wordpress.org/andy/) * [ Andrew Nacin ](https://profiles.wordpress.org/nacin/) * [ Barry ](https://profiles.wordpress.org/barry/) * [ Erick Hitter ](https://profiles.wordpress.org/ethitter/) * [ nickdaugherty ](https://profiles.wordpress.org/nickdaugherty/) * [ Mohammad Jangda ](https://profiles.wordpress.org/batmoo/) * [ Simon Wheatley ](https://profiles.wordpress.org/simonwheatley/) * [ jenkoian ](https://profiles.wordpress.org/jenkoian/) * [ Boro Sitnikovski ](https://profiles.wordpress.org/bor0/) * [ Andrija Vučinić ](https://profiles.wordpress.org/aidvu/) ## Support Got something to say? Need help? [View support forum](https://wordpress.org/support/plugin/memcached/)