When scaling a high traffic site running drupal the underlying problem is often to serve the same content to numerous users or at least to behave as if one need to have the whole database and content potentially accessible by requests triggered by numerous users.
Now what would be the relevant solution when each user need mainly to interact with his own content ? Think for example to a personal note taking site with large number of users.
One could think of having multiple servers each one devoted to a different set of users. Each server would be running independently the same full LAMP+ drupal and each would have only the database portion corresponding to its set of users. Scaling would mean then essentially adding a new server instance for new group of users and "balancing" users on the relevant server.
Is there any known tools for implementing things that way ? is it viable ?