Yes, as written before, memcached is already running on 127.0.0.1 and port 11211. I can confirm this by looking at currently running processes

grep memcached
memcache 22441 0.0 0.0 348996 15408 ? Ssl Feb02 0:20 /usr/bin/memcached -m 512 -p 11211 -u memcache -l 127.0.0.1

So, to quote the link from Denis:

"Since config.php array is merged to the whole config, you can replace any Yii params in the config.php file.

The Yii specific settings are set in the components array..."

This is new to me and now I know that I just place it somewhere in the config.

I will test it right away.

Thanks a lot for helping. It's now working . I got it first wrong and the backend didn't start up, but now as it is fully functioning, I assume memcached is used.

Is there a way to check it to be sure?

Thanks!

Maybe check memory usage ?

serverfault.com/questions/201814/memcached-memory-usage

Or :
github.com/elijaa/phpmemcachedadmin

It says 300MByte, so something must be in there