I find from the ISPConfig 3.1 manual, the installation includes php-memcached opcache apc. All of them are able to be cache of php. Is it possible to disable some of them in order to increase the free memory and without decreasing the php performance?
They are all for different purposes: php-memcached is the PHP driver that allows PHP to connect to a memcache daemon, so this is not a PHP cache. Opcache is the standard PHP binary cache in recent PHP versions. APCu is a extension for Opcache which simulates APC so some older software that uses APC specific caching functions is able to connect to Opcache. If yur software does not use memcache, then remove the memcache driver. If your software does not use APC functions, then disable APCu.
