Possible hacking attempt. How to tell if my db has been compromised

Something (probably a bot) is scanning your web server for those pages, which do not exist since they are receiving 404 errors. The scanning is very common -- usually scripts are looking for vulnerabilities.

We can't tell if your database has been compromised. Although the log contents you posted do not indicate that you have been compromised, just scanned.

This is a common attempt at finding out if there is an administrative web interface installed at the site. It's normal for any web site to receive such attempts from time to time.

If this is a traffic log, this particular attempt rendered no success at all as all requests resulted in a HTTP 404. If this is just a report of error messages, you should look at the traffic log to see if any request from that IP resulted in a non-404 response.

Still, just because such an attemt would find a web interface it was looking for doesn't mean that it has been hacked. It only means that someone knows what web interface you are using, and could try to find a security weakness in it. Generally there is very little risk for that if the system is properly updated and patched.