An object cache can help speed up database queries by caching the results of those queries in memory. One of the most popular object cache is MemCached. Support for this is included as part of the core WPCloudDeploy plugin. An additional object cache option is REDIS which we also support in core (as of WPCD 5.6)
To enable Redis, the package first needs to be installed at the server level. If you’re running WPCloudDeploy 5.6 or later, all new servers will have it automatically installed. For older servers you can install it as follows:
A popup will appear that will offer periodic feedback as the process progresses. When the process is complete you will get a popup confirmation message and the black ‘terminal” window will show the actions that were taken while attempting to install the package.
Once it’s installed, you can then enable it on a site-by-site basis.
Once Redis has been installed on a server you can activate it for any site on the server.
After a while the screen will refresh – if the operation is successful. If the operation fails, you’ll get a popup confirmation message and the page will refresh.
You can view a full log of the operation under the SSH LOG screen.
To deactivate Redis on a site:
After a while the screen will refresh – if the operation is successful. If the operation fails, you’ll get a popup confirmation message and the page will refresh.
You can view a full log of the operation under the SSH LOG screen.
Warning: Before removing Redis from the server, make sure you deactivate it from all sites on the server. Otherwise, you’ll see heavy delays when you access your site because WordPress will be attempting to connect to a non-existent Redis server.
To remove it:
If this procedure does not work, you can remove it using the command line on the server.
Amazon AWS has an article that outlines some of the differences between REDIS and MEMCACHED. Most of these differences do not matter in WordPress because the REDIS cache plugin doesn’t take advantage of them. MemCached uses a multi-threaded architecture which can be useful on a multi-core VM. But REDIS, in general, is more flexible.
In WordPress, MemCached can only use a max size of 1 MB for an object. Sometimes, WordPress objects in MemCached are larger than 1 MB because the options table is just HUGE. This will cause MemCached to actually SLOW DOWN or TIMEOUT your WP site. Redis is substantially better in theses situations.
Generally, given a choice between REDIS and MEMCACHED, we’ll choose REDIS.
If you do not want REDIS to be automatically enabled for all your new sites there is an option to make that happen:
You can apply a label next to the titles on the SERVER and SITES list that show which object cache (Redis or Memcached) is enabled. To turn this on: