Why is database connection expensive to create ? Like what finite resource (bandwidth/network round trip/cpu) exactly is it consuming ?
Typically expensive to create means it is consuming some resource like cpu/disk/io, but in case of connection i can only think of the time it takes for Sync/Ack etc.
You didn't say what database you are asking about, so this answer is pretty generic.
Database connections are much more than just a TCP/IP socket. Each connection consumes memory that associates the user with various resources in the database. It will likely use up some memory blocks from a shared memory pool, etc. Just authorizing the connection will run several queries, depending on the connection string. First the user will be authenticated. If an "initial-catalog" is specified, then an authorization will be performed as well. And if there is some sort of auditing going on, then the connection will be logged somewhere.
