Tim Hunt

File copy tools like FTP can sometime screw up like this. That is actually a good arguemnt for using git to adminster your Moodle site if you can. It can verify that the files on your server exactly match what should be there. See http://docs.moodle.org/23/en/Git_for_Administrators

1. I am hoping that MDL-34399 will greatly improve quiz performance in Moodle 2.4+

2. You probably could make a plug-in to implement your idea. See http://docs.moodle.org/dev/Quiz_access_rules.

3. I had another idea recently. Start attempt is much more expensive than continue-attempt, so it would be cool if you could pre-generate the new attempt for each student in advance, and then when the student clicks the "Start attempt" button we would only have to retrieve the existing attempted and fill in the start time. Coding that would be a bit harder, and would require changes to the core quiz code, but if anyone gets really desparate for high numbers of concurrent quiz attempts, then this is probably doable. (But it does not solve the problem with lots of simultaneous "Submit all and finish"es to process when time expires, if you have a time limit.)