There are a couple steps that have large alter table queries (that may take MySQL a while, depending on your server configuration and DB size). If you have a large forum, you may wish to use the CLI upgrade. Otherwise, simply refreshing should be fine.
This is likely caused by an add-on conflict. You may need to restore a backup, remove the offending add-on data from the database, and retry the upgrade. Contact support if you are not sure how to proceed.
My upgrade always falls over at step 10/11. As Mike says there are some intensive ALTER queries running on the posts table. Any sizeable board could easily time out on this step. I Defo recommend the CLI upgrade option..... Its painless.
If the board upgrade message is showing, then the upgrade didn't finish. You need to go back to the upgrade system and pick it up again. (You may want to look at the MySQL process list / server load to determine if the alter is still running; if it is, there's not a lot that can be done until it's finished. You will want to check your MySQL config for the future though.)
I restored the DB and the files. I uninstalled most add-ons, upgraded those that were left and then disabled all of them before running an upgrade. The upgrade script is just stuck on the Upgrading... 1.2.0 Alpha, Step 10 for the last 5 or more hours.
This upgrade is the most frustrating ever in the last 8 years of running a forum.
Alright I checked the mysql processlist and there were no processes running except the one to check the processlist. So I ran the CLI upgrade and it is showing Upgrade completed successfully. I cannot believe my eyes so just want to ask, does that mean everything went fine or will I discover missing tables/columns later?