Presently, I receive the following the warning on the Administration / Overview page:
No memory cache has been configured. To enhance performance, please configure a memcache, if available. Further information can be found in the documentation.
The referenced manual page includes the following:
There are two types of caches to use: a PHP opcode cache, which is commonly called opcache , and data caching for your Web server.
In the local PHP instance, OPcache is enabled. I find no other requirements given in the documentation for the application using caching.
What further configuration is required to remove the warning in the administration page?
Reading the document you referenced, the same that I quoted earlier, during a second sitting, I now begin to understand the intention to express that use of opcode and memory caching are separate decisions, either or both being active or inactive in some deployment.
Simple changes to the structure of the page would help clarify this relationship, for example, moving the discussion of opcode caching to a separate section at the same level as the much larger discussion about memory caching.
Keep in mind that the sequence of events in this case is that the user visits the settings pane in the application, reads the warning text, and then follows the reference given in that text. The user is given no explicit indication that the reference describes any type a caching unrelated to the reference, and is instead primed to consider the entire discussion as directly relevant to the warning.