What Is Oracle Database Compatibility?

Before you upgrade, review compatibility between your earlier release Oracle Database and the new Oracle Database release as part of your upgrade plan.

Understanding Oracle Database Compatibility

If new features are incompatible with your earlier release, then Database compatibility can cause issues.

Databases from different releases of Oracle Database software are compatible if they support the same features, and if those features perform the same way. When you upgrade to a new release of Oracle Database, certain new features can make your database incompatible with your earlier release.

Your upgraded database becomes incompatible with your earlier release under the following conditions:

  • A new feature stores any data on disk (including data dictionary changes) that cannot be processed with your earlier release.

  • An existing feature behaves differently in the new environment as compared to the old environment.

When to Set the COMPATIBLE Initialization Parameter in Oracle Database

Oracle recommends increasing the COMPATIBLE parameter only after you have completed testing the upgraded database.

After the upgrade is complete, you can increase the setting of the COMPATIBLE initialization parameter to the maximum level for the new Oracle Database release. However, after you increase the COMPATIBLE parameter, you cannot subsequently downgrade the database.

The COMPATIBLE Initialization Parameter in Oracle Database

Review to understand how to set the COMPATIBLE initialization parameter for non-CDB and multitenant architecture containers.

Oracle Database enables you to control the compatibility of your database with the COMPATIBLE initialization parameter.

Understanding the COMPATIBLE Initialization Parameter

In Oracle Database 19c, when the COMPATIBLE initialization parameter is not set in your parameter file, the COMPATIBLE parameter value defaults to 19.0.0 If you do not set the COMPATIBLE initialization parameter to 19.0.0, then you cannot use the new Oracle Database 19c features, because your upgraded database is not running in the required COMPATIBILITY setting for Oracle Database 19c features.

When the Oracle Database COMPATIBLE parameter is increased to 19.0.0, the first Java call to the database initiates a "name translation" operation. This operation can require a few minutes to complete. You should expect this delay the first time a Java call is made to the database after you increase the compatibility parameter. This initial delay to carry out the name translation occurs only during the initial Java call.

Note:

  • Before upgrading to Oracle Database 19c, you must set the COMPATIBLE initialization parameter to at least 11.2.0, which is the minimum setting for Oracle Database 19c.

  • The compatible parameter must be at least 3 decimal numbers, separated by periods. For example:

    SQL> ALTER SYSTEM SET COMPATIBLE = '12.1.0.2' SCOPE=SPFILE;
  • Oracle recommends that you only raise the COMPATIBLE parameter after you have thoroughly tested the upgraded database.

  • After you increase the COMPATIBLE parameter, you cannot downgrade the database.

Caution:

If you are upgrading from Oracle Database release 11.2, then you must set the compatible value to at least 11.2.0. You must do this at the time of the upgrade. Do not make this change until you are ready to upgrade, because a downgrade back to an earlier compatibility level is not possible after you raise the COMPATIBLE initialization parameter value.

See Also:

Oracle Database Administrator’s Guide for information about managing initialization parameters

Rules for COMPATIBLE Parameter Settings in Multitenant Architecture

The COMPATIBLE parameter of the container database (CDB) affects the COMPATIBLE parameter settings of pluggable databases (PDBs) plugged into that container database. Review the following scenarios that occur when you plug in a PDB to a CDB:

  • PDB COMPATIBLE equal to CDB$ROOT COMPATIBLE parameter setting.

    Result: No change to the PDB COMPATIBLE parameter setting.

  • PDB COMPATIBLE is lower than CDB$ROOT COMPATIBLE parameter setting.

    Result: The PDB COMPATIBLE parameter is increased automatically to the same COMPATIBLE parameter setting as CDB$ROOT. After you plug in the PDB, you cannot downgrade the PDB to an earlier release.

  • PDB COMPATIBLE is higher than CDB$ROOT COMPATIBLE parameter setting.

    Result: The PDB cannot be plugged in. Only PDBs with a COMPATIBLE parameter setting equal to or higher than CDB$ROOT can be plugged in to the CDB.

Values for the COMPATIBLE Initialization Parameter in Oracle Database

Review to find the default, minimum, and maximum values for the COMPATIBLE initialization parameter.

The following table lists the default, minimum, and maximum values for COMPATIBLE in Oracle Database 19c, and in each release supported for upgrading to Oracle Database 19c:

Table 1-2 The COMPATIBLE Initialization Parameter

Oracle Database Release Default Value Minimum Value Maximum Value
Oracle Database 19c

19.0.0

11.2.0

The COMPATIBLE parameter should not be changed for an RU or an RUR, either for CDB or Non-CDB instances.

Oracle Database 12c Release 2 (12.2)

12.2.0

11.2.0

12.2.0

Oracle Database 12c Release 1 (12.1)

12.0.0

11.0.0

12.1.0

Oracle Database 11g Release 2 (11.2)

11.2.0

10.0.0

11.2.0

About Downgrading and Compatibility for Upgrading Oracle Database

Before upgrading to Oracle Database 19c, you must set the COMPATIBLE initialization parameter to at least 11.2.0.

After upgrading to Oracle Database 18c, you can set the COMPATIBLE initialization parameter to match the release number of the new release. Doing so enables you to use all features of the new release, but prevents you from downgrading to your earlier release. Only a subset of Oracle Database 18c features are available while the COMPATIBLE initialization parameter is set to a lower value.

Caution:

After you increase the COMPATIBLE parameter, the database cannot be downgraded.

How the COMPATIBLE Initialization Parameter Operates in Oracle Database

The COMPATIBLE initialization parameter enables or disables Oracle Database features based on release compatibility

The COMPATIBLE initialization parameter operates in the following way:

  • The COMPATIBLE initialization parameter enables or disables the use of features, to help protect your existing application use of data.

    If you run an Oracle Database 12c database with the COMPATIBLE initialization parameter set to 11.2.0, then the database software generates database structures on disk that are compatible with Oracle Database Release 11g release 2 (11.2). If you try to use features that are part of a later release of Oracle Database, and make the database incompatible with the COMPATIBLE initialization parameter, then an error occurs. However, new features are enabled that do not create changes on disk that are incompatible with Oracle Database Release 11g release 2.

  • If you make changes to the database that make the database incompatible with the COMPATIBLE initialization parameter setting you want to use, then the database does not start, and initialization terminates in an error. If this happens, then you must set the COMPATIBLE initialization parameter to an appropriate value for the database.

See Also:

Oracle Database Concepts for more information about database structures

Checking the Compatibility Level of Oracle Database

Use this SQL query to check that the compatibility level of your database corresponds to the value of the COMPATIBLE initialization parameter:

SQL> SELECT name, value FROM v$parameter
         WHERE name = 'compatible';