Memcached is a service that allows entire database tables to be stored in memory, drastically speeding up queries to those tables and alleviating database load. In Drupal, the Memcached module allows you to store all cache tables in memory.
We've covered how to install Memcached before on Debian and on Mac OS X. But server software can vary significantly between sites, and this guide can be used to set up Red Hat Enterprise Linux (RHEL) or CentOS, which are architecturally the same.
Install memcached through RPM
The easiest way to install Memcached is through a package manager such as yum or apt. However, Memcached is not available from the default collection of packages, so the first thing we need to do is add a new RPM (Red Hat Package Manager) server so that we can install Memcached through yum.
One of the best 3rd-party RPM servers is provided by Dag Wieers, which will provide us with up-to-date packages that are not provided by Red Hat directly. The one tricky part of setting up an RPM server is making sure you get the repository that matches your server version and architecture (32-bit or 64-bit). So we need to collect that information first.
From a shell prompt, get the CentOS/RedHat version number:

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