We have already upgraded Oracle Database11gR2 to 12c, the whole process is still relatively smooth, although some of the previous version of the upgrade is not the same, but the overall difficulty is not too large, because of too many different features, greatly extended the upgrade time.

But for Oracle 12c back to the previous version, there will be some restrictions, only downgrade to the version and patch level used before the upgrade.

  • If we are upgrading directly from 10.2.0.5 , 11.1.0.7 or 11.2.0.2 and above. Although it is possible to upgrade 10.2.0.5 directly, downgrade does not apply to 10.2.0.5 .
  • If any patches are applied to the source database that is running from the upgraded home directory, you need to roll back before you start the downgrade process.

Firstly, start the inspection before the downgrade operation
Ensure that all components are in a normal state before upgrading without invalid components.

Check the state of each component

Check invalid components

Second, began to implement downgrade operations

  • Shut down the database

  • Start the database to downgrade mode

  • Run the downgrade script

Now modify /etc/oratab for Oracle 11gR2 HOME directory

Additionally, modify the system environment variables

After that start to upgrade mode, execute the catrelod script from the downgraded version $ORACLE_HOME/rdbms/admin directory.

Now check the registry components.

Now execute utlrp.sql script Recompile all existing PL/SQL modules in the INVALID state

After executing the above script before making a check, Now there is no invalid objects

Lastly, Restart the database.

Stay Tuned for Downgrade the Oracle RAC Database.

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