During a SonarQube upgrade, Tables may be copied entirely (that speed up the migration process, to benefit from sequential write).
The effect is that in the worst-case scenario, the database could double the used disk space.
Users need to be mindful about this, and make sure in advance they have plenty of free disk space on their database before starting a migration.
As a rule of thumb, the database disk usage should be below 50%, to allow all tables to be temporary duplicated.
The disk space is then free at the end of the migration.