When do changes to the DNS configuration file take effect?

I was reading around the forum and saw a comment that edits to the DNS config file do not need a restart of the DNS server to take effect. I just wanted to confirm that. I have just a little experience with Unix config files for Apache and Apache needs to be restarted to have configuration changes take effect. Is it correct that the DNS server reads the file each time it responds to a request? Seems a bit inefficient. Nice to have config change take effect with each edit, but it would be a shame if a partial edit to the config file hosed the system.