by Ken Task.
I hope you are making the db tweaks with some information from something like MySQLTuner ... sometimes one can get a point where config changes for DB upwards actually begets diminishing returns.
I'll give it another 'guess' ....
Is the 2.2 site still up and can you get to that course there?
If so, reset that course ... that will remove students *and their work* ... quizzes and quiz attempts.
Make no user backup of that reset course - just to make sure nohting of students is contained in the backup.
Since you've learned how to inspect a backup, un-compress and look at the xml flies ... sizes.
Must say that's one large 'quiz'!!!! :\
Something else if the 2.2 site is still up .... can you export the quiz bank?
Am also gonna stick my neck out and say you're only hope might be moosh from command line. Takes browser out of loop ... apache out of loop ... just PHP and DB server then.
Will send a PM with some other strategy to assist.
'spirit of sharing', Ken