auto vacuum

I have a db that stores real time data for a scada system. I've noticed
that when it uses postgres it fills the hard drive with 1GB files
in the data folder. I've tried to set the auto vacuum parameters but it
looks like auto vacuum won't work when the tables
are being accessed. These systems are continuous process control systems
so I can't stop them at any particular time.

I see that I can run a full vacuum manually and that more or less works with
things running so I thought that I would
schedule that. I wanted to write a simple script or batch file but it
requests a password and it doesn't seem to take one
from the command line.

This doesn't seem like such an unusual problem so I was wondering how people
generally deal with this. I would prefer
not to switch to MySql.