asterisk users - Jan 2007 - Recompiled app_xyz.so and Asterisk Dynamic Loader

Hi,
 I would like to know what is "Asterisk Dynamic Loader". Let me
explain what I'm about to ask.

I have three Asterisk servers running my in-house built app_xyz.so
application. Now what I do to save time is compile application on one
server and scp app_xyz.so on rest of servers. All servers have same
OS, H/W specs. Today I checked the logs and observed that at the time
when app_xyz.so was copied on Server-1,2, asterisk restarted. The last
line before restart was Asterisk dynamic loader sort of debug message.
and show uptime was give exact restart time since reloaded.

Now my concern is
1. What about the running sessions at that time,  they were hunged up
by asterisk forcefully ? Because I didn't see the logs of that session
afterwards.
2. Do I really need to restart asterisk gracefully to reload new
modified app_xyz.so application to make changes effective on
production?

Thanks!
-ag