We are currently running a Perl web application on top of Apache 1.3 (I know this is seriously outdated but there is nothing we can do about it at this time). Throughout the day, as the number of users accessing the application increases, the server becomes less and less responsive until it eventually becomes unavailable. At this point we stop the Apache server until there are no active connections and then the server is restarted. This is far from an ideal solution and doesn't resolve the underlying issue.
What can we do to find the root cause of our problem and what can we do to resolve the issue in the short and long term?