Configuring WordPress to use Memcached

When using WordPress self hosted software it’s generally a good idea to cache as much as possible.  Object Caching allows you store parts of the pages in memory for quicker retrieval, since the server will not need to look as much up from the SQL database.

Installing the needed parts

To start out, you will need to have memcached installed on your server. If your using Fedora, you may install memcached via Yum as follows.

yum -y install memcached php-pecl-memcached perl-Cache-Memcached

Configuring memcached

After installing memcached you need to configure it. If working in Fedora, and using the Yum install as talked about above, you will need to change the memcached confuration by modifying it’s sysconfig file located at /etc/sysconfig/memcached.

A default configuration may look like this.

PORT="11211"
USER="memcached"
MAXCONN="1024"
CACHESIZE="64"
OPTIONS="-l 127.0.0.1"

If you would like to share this memcached server with other webservers, change the address from 127.0.0.1 to the server’s actual address.

To set memcached to start automatically when the server get’s rebooted, run:

chkconfig memcached on

And of course, don’t for get to start it

service memcached start

Configuring WordPress

After memcached is installed, you need to configure the WordPress side.

Next you should install the Memcached Object Cache plugin, but be careful, this is not a normal plugin.  You should not activate this plugin as you would with a normal plugin, but instead download it as you normally would, but then you need to copy the object-cache.php file to your wp-content folder.

From the root of your WordPress install, run the following:

cp wp-content/plugins/memcached/object-cache.php wp-content/

Now we need to configure WordPress to use the memcached server. Add the following near the end of your wp-config.php file.

global $memcached_servers;
$memcached_servers = array('default' => array('127.0.0.1:11211'));

Note that were using the same server and port (127.0.0.1:11211) as was configured above while we were setting up memcached.

Checking in on memcached

Memcached is one of those things that just sort of runs. There’s not much direct feed back, besides the speed difference on your site.

One quick way is memcache-top. memcache-top will show you the current status of your memcached server.

To install, run the following.

wget http://memcache-top.googlecode.com/files/memcache-top-v0.6
chmod +x memcache-top-v0.6
./memcache-top-v0.6

Running ./memcache-top-v0.6 will assumed the default configuration we used here.

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