@Alan_SP
I have added some comments to the specific DevBlog article, please read them for general background information.
However, the DevBlog article is somewhat irrelevant, that is, to some degree.
The php memcached module is already included in the php 5.6.12 version in Plesk 12.5.30, so compiling it (with PECL) is not required: just activate or deactivate via the Contol Panel.
If you want to use the php memcached module in Plesk 12.0.18, just read my comments in the DevBlog article.
With respect to Redis Cache, the following.
In essence, the php redis module is also included in the php 5.6.12 version in Plesk 12.5.30 and activation/deactivation via the Control Panel will suffice.
Note that you have to install the Redis server and also note that it is adviceable to uninstall a Memcached server (if any is present), before installing Redis server. This will certainly prevent some problems that can occur when both the php memcached and the php redis module are activated at the same time.
As a final note, the activation of the php memcached and/or php redis modules does not imply that the cache gets used (i.e. "hit" is the proper term).
The before mentioned modules simply allow the usage of a particular caching mechanism.
It is up to the "programmer/developer" to specify whether and in what way the cache will be used.
For vBulletin, a implementation of the memcached caching mechanism is already defined.
In contrast, the implementation of the Redis caching mechanism for vBulletin is barely existing.
However, one should be able "to borrow" some of the Redis implementations for WordPress, even though one has to be very careful in doing so.
But why does one want to experiment with Redis for vBulletin, if memory caching and/or memcached caching is already available?
A set of simple reasons: Redis is
- in-memory AND out-of-memory (i.e. disk-based), with optimal algorithms for distributing cache over memory and disk,
- much more flexible than Memcache(d),
- very, very much faster than Memcache(d).
Nevertheless, vBulletin + Redis seems to be something for the future.
In conclusion, try to get the php memcache module working first.....
Regards....