Killing active users

Hi:

I have a system where I have 2 DBs. The first is available to the users
for general interaction. The second gets reloaded with new data once
per night and is then "renamed" to the active one if/when the reload
went successfully, preserving the old DB as a standby. Here's a
snapshot of that process.

alter database maindb rename to temp;

alter database standby rename to maindb

alter database temp rename to standby

The problem is that sometimes the rename fails because there are active
users on the available DB... DBD::Pg::db do failed: ERROR: database
"maindb" is being accessed by other users . Because the reload takes
place in the wee hours, I feel it's OK to kill any existing user
connections in order to prevent this if I have to.

Q: Is there a way to kill all active users on a DB without having to
reboot the DB?

Q: Or is my problem moot in that there is a way to leave those
connections alone and attached to the now renamed DB?

Thanks in Advance for any help

-dave