The COMPATIBLE Initialization Parameter and Irreversible Compatibility (119)

The COMPATIBLE initialization parameter enables or disables the use of features in the
database that affect file format on disk. For example, if you create an Oracle Database
10g database, but specify COMPATIBLE = 9.2.0.2 in the initialization parameter
file, then features that requires 10.0 compatibility will generate an error if you try to
use them. Such a database is said to be at the 9.2.0.2 compatibility level.

You can advance the compatibility level of your database. If you do advance the
compatibility of your database with the COMPATIBLE initialization parameter, there is
no way to start the database using a lower compatibility level setting, except by doing
a point-in-time recovery to a time before the compatibility was advanced.

The default value for the COMPATIBLE parameter is the release number of the most
recent major release.

Note: For Oracle Database 10g Release 2 (10.2), the default value
of the COMPATIBLE parameter is 10.2.0. The minimum value is
9.2.0. If you create an Oracle Database using the default value, you
can immediately use all the new features in this release, and you
can never downgrade the database.

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