With the release of SlimServer versions 6.5.0, the MySQL database has become the default storage engine that the application uses to hold all information about the user's music library and playlists. MySQL offers a number of performance improvements over SQLLite, particularly in the query engine.
MySQL is a high performance, robust and reliable database server that is used by millions of users worldwide, and is behind applications including Wikipedia and Google. So - you can rely on it to keep track of your music library!
When you install a SlimServer version 6.5.0 to version 7.6.0 you will also be installing an embedded version of MySQL that will only be used by SlimServer. You will not have to perform any administration tasks with this server directly and to all intents and purposes it's hidden from view and will look after itself.
If, however, you have an existing MySQL installation running on your machine (for example, you may have other applications that already use it), you can optionally ask SlimServer to use your instance rather than starting its own and save some system resources. See the ExistingMySQLInstance page for further details on this process. Note that this is entirely optional - SlimServer's MySQL instance will happily run alongside your existing MySQL installation without interference.