memcached != memcache

does it mean memcached interexchanged with memcache ? otherwise speaking are you trying to say that memcached=memcache ? I think what are u r saying is memcached can not be quantified  memcache  as they are different. 

So, will the following in setting.php solve 

You need PHP extension php-memcached and memcached server only.

In Elgg settings.php use:

$CONFIG->memcache = true;

$CONFIG->memcache_servers = array (
    array('localhost', 11211),
);

// Namespace prefix means some name if you use multiple sites on your server​
$CONFIG->memcache_namespace_prefix = 'site_name';

Please, read how to install PHP 7 with memcached.

And Elgg docs also.

are you trying to say that memcached=memcache ?

These are different extensions (modules).

!= means NOT