MemcacheD Is Your Friend is an object caching plugin for WordPress that offers faster access to cached objects, especially if your database happens to reside on a different host. The problem this time around is that it scopes some of its members as private, and as a result, is incompatible with some plugins. I’ve run into this before when trying to import data into WordPress.
This time, I was trying to get Elasticpress working on a site where the Memcached object cache was already set up. Thankfully, someone on a Github support thread helpfully pointed to a fork they made of the long-neglected Memcached Is Your Friend plugin. I haven’t had a chance to try it yet but wanted at least a placeholder here to it in case it comes up again.