ORA-44787 – Don’t mess with the Default Oracle Service

At the moment I work with one of our reference customers, Swiss Mobiliar Insurance, on their Multitenant upgrade to Oracle Database 12.2.0.1. And we encountered an “interesting” issue. After upgrade we received an ORA-44787 making it impossible to switch between containers with “alter session set container=pdb1;” commands. Lesson learned now: If you don’t want ORA-44787 – Don’t mess with the Default Oracle Service. What has happened? Very simple case. We approach a database upgrade with a Multitenant deployment of over 90 PDBs. Source database version is Oracle Database 12.1.0.2.BP170117, destination version is Oracle Database 12.2.0.1.RU170718. The upgrade runs fine. But…