When upgrading WordPress:

  1. Make backups.
  2. Deactivate the plugins.
  3. Make another backups by a different methods in case the first backup is bad.
  4. If something goes wrong, make sure plugins are deactivated.
  5. Hey, it's cheap. Make yet another backup.
  6. Make sure plugins are up-to-date.
  7. Aw heck, make one more backup.

You might notice that over a year of UnSpace is now missing. I:

  1. Made a backup.
  2. Didn't deactivate the plugin.
  3. Didn't make a second backup.
  4. When something went wrong, I didn't make sure the plugins were deactivated.
  5. I do have a damaged file that MySQL won't open because it's damaged.
  6. A plugin wasn't up-to-date, and that was causing the problem.
  7. My next earlier backup was from July of last year.

I might be able to salvage the posts and comments if I can find some way of opening a damaged MySQL file.

Live and learn.