I'm not clear on the difference between reload and restart as in :
apachectl restart | reload | stop | start

From my reading of the scripts, it looks like reload kills all processes but the parent and restart kills everything before starting.

Is that correct. Is there anything else? I'm particularly interested in knowing what happens to existing sessions, for example, a user in the middle of a multi-page signup process.

i am not sure but i guess restart is used to restart the daemon and reload is used so that daemon re reads the configuration file.

That was my assumption at first too, but I think there is more to it than just re-reading the config file.

man apachectl

on my system (apache 2.2.9) I do not have a reload. Typically in start up scripts, reload is the same as restart.

I do however have
restart and graceful

the man file says that graceful will not terminate open connections and the logfile will not be closed immediately. I would only assume that a regular restart would forcefully stop everything.

I think reload won't stop the daemon but reread the data from configuration files

am I correct?

I think 'reload' might be a misnomer. After reading the init scripts that call it, I see this:
reload() {
echo -n $"Reloading $prog: "
if ! LANG=$HTTPD_LANG $httpd $OPTIONS -t >&/dev/null; then
RETVAL=$?
echo $"not reloading due to configuration syntax error"
failure $"not reloading $httpd due to configuration syntax error"
else
killproc $httpd -HUP
RETVAL=$?
fi
echo
}



The function killproc is located in /etc/init.d/functions (this is a Centos system). It appears to me that killproc is a more feature-rich version of kill.
My shell script abilities are less-than-expert but it appears to me that 'reload' is not much different than 'restart'. If you want to minimize the affect on users, then 'graceful' seems to be the correct way.