Hardware and performance

Follow up:
I saw that memcached has a lot of API's - including php and mysql.

In my case with two webservers and the single db server;
should I install the memcache alongside eaccelerator on the webservers AND on the DB server?

or should I leave eaccelerator alone on the front-end and install memcache on the backend alone

Thanks for the assistance.

Regards,
-n