What is the relationship between a SPID and a Connection in SQL server?

Question

Can a SPID be used by two connections, while both connections are open?

If a connection is returned to a connection pool, will it hold on to the SPID?

Answer 1

Can a SPID be used by two connections, while both connections are open?

No, each open connection will have its own SPID.

If a connection is returned to a connection pool, will it hold on to the SPID?

Yes, as long as the connection is open, it will be associated with one SPID.

You can test this yourself by querying sys.sysprocesses. Rebooting a client machine should clear its connection pool.