There are several modes to stop the server, depending on the level of urgency. We'll do a comparison in view of the effects in each mode.
You can issue a database server
stop command using fast mode, as follows:
pg_ctl -D datadir -m fast stop
You must use
-m fast if you wish to shut down as soon as possible. Normal shutdown means "wait for all users to finish before we exit". That can take a very long time, though all the while new connections are refused.
On Debian/Ubuntu systems, this command can be as follows:
pg_ctlcluster 9.0 main stop --force
When you do a fast stop, all users have their transactions aborted and all connections are disconnected. This is not very polite to users, ...