The behaviour of these functions is affected by settings in
Table 7.46 Mysqlnd_memcache Configure Options
|mysqlnd_memcache.enable||1||Available since 1.0.0|
Here's a short explanation of the configuration directives.
This option is mainly used by developers to build this extension statically into PHP. General users are encouraged to build this extension as a shared object, and to unload it completely when it is not needed.