Hi,
It's done automatically by digiKam. The internal server want mean a stanalone instance of mariadb or mysql storing database in local, and queried through a local socket. The server is not available outside of course. It's "internal".
So typically it's a replacement of sqlite for huge collection, even if sqlite work better and better in this case, since it used everywhere for local database. LightRoom for ex, use sqlite...
And this is a problem for LightRoom which cannot be used through the network, due to technical limitation of sqlite in this context.
Gilles Caulier