Upgrading the PDB$SEED takes always longer than any other container.
What is the reason for an upgrade of the PDB$SEED taking so much longer in a real world environment?
How does an upgrade with Oracle Multitenant work?
I have written several blog posts in the past about the different techniques to upgrade an Oracle Multitenant environment:
The interesting case happens in the “Everything At Once“. The PDB$SEED takes significantly longer to upgrade than any other container.
Upgrading the PDB$SEED takes always longer?
Quick recap: The PDB$SEED is the (I call it) blueprint PDB which gets used to provision a new PDB quickly as a clone of the PDB$SEED with some additions. It is (for users) always READ ONLY and UNTOUCHABLE. This means, as a user you are not allowed to touch or change or modify or manipulate it. If you still do so, you’ll hit “unsupported” territory.
Here you’ll find a complete example for an Everything At Once upgrade:
As the PDB$SEED is read only and untouchable, a design decision has been taken to RECOMPILE all invalid objects within the PDB$SEED container while the PDB$SEED is in UPGRADE mode. All other containers get recompiled AFTER the upgrade itself has been finished.
This is the reason why the upgrade of the PDB$SEED takes longer than expected.
When you look into the log files post upgrade you will spot the reason for the longer duration of the PDB$SEED upgrade (marked in RED below):
Oracle Database 12.2 Post-Upgrade Status Tool 05-09-2017 14:46:01 [PDB1] Component Current Version Elapsed Time Name Status Number HH:MM:SS Oracle Server UPGRADED 220.127.116.11.0 00:32:28 Oracle Real Application Clusters UPGRADED 18.104.22.168.0 00:00:00 Oracle XML Database UPGRADED 22.214.171.124.0 00:02:24 Final Actions 00:06:59 Post Upgrade 00:03:07 Total Upgrade Time: 00:45:31 [PDB1] Oracle Database 12.2 Post-Upgrade Status Tool 05-09-2017 15:03:52 [PDB$SEED] Component Current Version Elapsed Time Name Status Number HH:MM:SS Oracle Server VALID 126.96.36.199.0 00:32:24 Oracle Real Application Clusters OPTION OFF 188.8.131.52.0 00:00:00 Oracle XML Database VALID 184.108.40.206.0 00:02:25 Final Actions 00:06:44 Post Upgrade 00:03:16 Post Compile 00:18:02 Total Upgrade Time: 01:03:24 [PDB$SEED]
Post Compile” phase does not exist for any other container as part of the upgrade.