Earlier versions of our installer may not have configured your system to automatically purge expired Keystone tokens. It is possible that your token table has a large number of expired entries. This can dramatically increase the time it takes to complete the database schema upgrade.
You can alleviate this problem by running the following command before beginning the Keystone database upgrade process:
keystone-manage token_flush
This will flush expired tokens from the database. You should arrange
to run this command periodically (e.g., daily) using cron.