Memcached Object Cache

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 on at least one server. Note the connection info. The default is 127.0.0.1:11211.

  2. Install the PECL memcache extension

  3. Copy object-cache.php to wp-content

  4. Add the WP_CACHE_KEY_SALT constant to the wp-config.php:

    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

September 12, 2022
Download zip. Upload object-cache.php file (not memcached folder, only object-cache.php) to wp-content folder. Add define('WP_CACHE_KEY_SALT','RANDOM SALT KEY'); to wp-config.php Add $memcached_servers = array( 'default' => array( '127.0.0.1:11211' ) ); to wp-config.php done.
April 1, 2021
Fatal error: Cannot redeclare wp_cache_add() (previously declared in /public_html/wp-includes/cache.php:30) in /public_html/wp-content/plugins/memcached/object-cache.php on line 23. UPD: To plugin author: Please make the "copy the file to wp-content instead of activating it in the backend" message more attractive! Works. The website speed become A BIT faster, but still too slow (WP 5.7, no other cache plugins).
April 1, 2019
Still works like clockwork! Thank you gents. You might want to consider updating the "tested up to". That is all 🙂
June 18, 2017
For my purposes, that assume a default configuration (of 'memcached'), this little plugin just works. And it seems to cache a wide variety of objects by design. It's important to follow the instructions carefully though, as this is a drop-in, the installation of which is not that, of a standard plugin. Dirk
Read all 18 reviews

Contributors & Developers

“Memcached Object Cache” has been translated into 1 locale. Thank you to the translators for their contributions.

Translate “Memcached Object Cache” into your language.

Interested in development?

Browse the code, check out the SVN repository, or subscribe to the development log by 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