Summary:
Ref T12987. I was focused on the RefCursor table and overlooked that we need some care on this key.
It's currently possible to run `bin/storage upgrade --no-adjust`, then start Phabricator, and end up with duplicate records in this table. If you try to run `bin/storage adjust` later, it will try to add the unique key but fail. This is unusual for normal installs (they usually do not use `--no-adjust`) but we do it in the cluster and I did this exact thing on `secure`.
Normally, to avoid this, when a new table with a unique key is introduced, we also add a migration to explicitly add that key.
This is mostly harmless in this case. Fix this mistake (force the table to contain only unique rows; add the key) and try using `LOCK TABLES` to make this atomic. If this doesn't cause problems we can use this in similar situations in the future.
The "alter table may unlock things" warning comes from here:
https://dev.mysql.com/doc/refman/5.7/en/lock-tables.html
It seems like it's fine to issue `UNLOCK TABLES` even if you don't have any locks, so I think this script should always do the right thing now, regardless of ALTER TABLE unlocking or not unlocking tables.
Test Plan: Ran `bin/storage upgrade -f`, saw table end up in the right state. I'll also check this on `secure`, where the starting state is a little messier.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T12987
Differential Revision: https://secure.phabricator.com/D18623
