asterisk users - Feb 2005 - do i have to reload asterisk every thing i add a neww extension

1.) do I have to keep reloading asterisk every thing I add a new extension 
or a new SIP user.
2.) is there a way to get the SIP users and the Extensions from a database.
3.) what can i do if i connect asterisk to mysql. i have seen this in 
voip-info site.