I have encountered this problem before (I had to reinstall a previous build from opmanger to restore our latest back-up and upgrade again) and the support engineer  (Tim Woods) stated the following:

".... It seems that the RAW data stored is very huge, it will take time to delete all the raw data entry. So, please allow the updatemanager to run, once it complete the upgrade steps start the OpManager service. Please do not  kill the process in between."

But there is not as much data as it was then

He looked at a file to check if it was still proceeding, but I can't remember which file anymore. How can I see if it is still upgrading or if it stalling?

Regards,

Raymond