Localdb !full! -

LocalDB subverts this model by introducing "user instances." When a developer connects to a LocalDB database, the engine starts up on demand. It spins up the sqlservr.exe process, attaches the database files ( .mdf and .ldf ), and executes the query. Crucially, when the connection is closed and a timeout expires, the process shuts down. This ephemeral nature transforms the database from a permanent infrastructure fixture into a temporary tool—closer to a text editor than a web server.