Database Reference
In-Depth Information
Here again it is beneficial to have a standard DBCA template or comparable method of creating databases
identically. After the pre-12c database has been migrated to the new release you can plug it into the CDB of your
choice, if the following prerequisites are met:
The target CDB and the newly migrated database MUST use the same or a compatible
character set and national character set.
The compatible parameter of the pre-12c database must be advanced to 12.1. Please
remember the warning of doing so: upgrading the compatible parameter rules a downgrade
by script out. Advance the parameter only if you are sure you will not need to downgrade to
the previous release.
Both target CDB and migrated database must have the same endianness. In other words you
cannot plug a database created on a popular RISC platform straight into a CDB running on
Linux.
Both CDB and migrated database must use the same options as shown in the
DBA_SERVER_REGISTRY view.
The last bit can be a problem on sites where is little control over the database creation process. The well-known
General_Purpose.dbc template seems to add every Oracle option under the sun to the database without the option
to change it during the creation. “Custom” databases quite often-and rightly so-contain only the options needed.
An engineered built ideally limits the options to the minimum required-catalog views and procedures as well as Java
and XML DB. Spatial, InterMedia and Text are not standard components and should be installed only when needed,
not the least to avoid license problems later!
Updating the compatible parameter
One of the steps after receiving sign-off from all stakeholders that the migration was a success is to bump the compatilibty
to 12.1. Again the word of warning-using a different compatible parameter will block the route to a downgrade via a script.
Before changing the parameter you should make sure you can revert to the pre-12c compatible setting. Usually a full
RMAN backup will be needed. Changing the parameter is rather simple but requires an instance restart. The command to
update the compatible settings is the usual alter system command:
SQL> show parameter compatible
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
compatible string 11.2.0.0.0
SQL> alter system set compatible='12.1.0' scope=spfile;
System altered.
SQL> shutdown immediate
Database closed.
[...]
Database mounted.
Database opened.
SQL> show parameter compatible
 
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