What Is Oracle Database Compatibility?

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

• About the COMPATIBLE Initialization Parameter in Oracle Database
  Review to understand how to set the COMPATIBLE initialization parameter for non-CDB and multitenant architecture containers in Oracle AI Database 26ai.
• Rules for COMPATIBLE Parameter Settings in Multitenant Architecture
  When you plug in PDBs to a later release CDB, the CDB$ROOT COMPATIBLE parameter setting can change the PDB COMPATIBLE parameter, or prevent plug-ins.
• Understanding the COMPATIBLE Initialization Parameter
  Learn about what the COMPATIBLE parameter does, when to raise the parameter release value, and what effects you can expect when you set the parameter to the new Oracle Database release.
• Understanding Oracle Database Compatibility
  If new features are incompatible with your earlier release, then updating database compatibility can cause issues.
• When to Set the COMPATIBLE Initialization Parameter in Oracle AI Database
  Oracle recommends increasing the COMPATIBLE parameter only after you have completed testing the upgraded database.
• Values for the COMPATIBLE Initialization Parameter in Oracle Database
  Review to find the default and minimum values for the COMPATIBLE initialization parameter for Oracle AI Database 26ai.
• About Downgrading and Compatibility for Upgrading Oracle Database
  Before upgrading to Oracle AI Database 26ai, you must set the COMPATIBLE initialization parameter to at least 19.0.0.
• How the COMPATIBLE Initialization Parameter Operates in Oracle Database
  The COMPATIBLE initialization parameter enables or disables Oracle Database features based on release compatibility.

About the COMPATIBLE Initialization Parameter in Oracle Database

Review to understand how to set the COMPATIBLE initialization parameter for non-CDB and multitenant architecture containers in Oracle AI Database 26ai.

You can ontrol the compatibility of your database with the COMPATIBLE initialization parameter.

Rules for COMPATIBLE Parameter Settings in Multitenant Architecture

When you plug in PDBs to a later release CDB, the CDB$ROOT COMPATIBLE parameter setting can change the PDB COMPATIBLE parameter, or prevent plug-ins.

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 lower than CDB$ROOT can be plugged in to the CDB.

Understanding the COMPATIBLE Initialization Parameter

Learn about what the COMPATIBLE parameter does, when to raise the parameter release value, and what effects you can expect when you set the parameter to the new Oracle Database release.

The default setting of COMPATIBLE sets the database release compatibility setting for the database, which determines which features are available in the database. To use new database features, you change the COMPATIBLE parameter setting to the new database release.

Caution:

In Oracle AI Database, the default COMPATIBLE setting value is different depending on your upgrade scenario, and the release updates to which you are upgrading. When the COMPATIBLE parameter is upgraded, you cannot change COMPATIBLE to a lower level of compatibility.

• New Installations of Oracle AI Database Release Update 23.9 and later: The database is installed with the COMPATIBLE parameter set by default to 23.9.0. You cannot downgrade the COMPATIBLE parameter to a lower level.
• New Installations of Oracle AI Database Release Update 23.6 and later: The database is installed with the COMPATIBLE parameter set by default to 23.6.0. You cannot downgrade the COMPATIBLE parameter to a lower level.
• Patches from Oracle AI Database Release Update 23.4 and 23.5: The database COMPATIBLE parameter remains at the settiing you had before patching (23.0.0 or 23.4.0 or 23.5.0). However, to use the new features for Oracle AI Vector Search, you must update the COMPATIBLE parameter to at least 23.6.0. Oracle Database release updates earlier than 23.4 cannot be patched or upgraded.
• Upgrades from Oracle Database 19c or 21c: The setting for COMPATIBLE remains the same as the setting you have in your source database. However, to use the new Oracle AI Vector Search features, you must manually set the upgraded database COMPATIBLE parameter to at least 23.6.0.
• Permitted COMPATIBLE values For upgrades, the permitted COMPATIBLE levels are 19.0.0 to the latest release. Values must be specified as at least three decimal numbers with each number separated by a period, such as 23.4.0 or 23.4.0.0

Note the following restrictions for COMPATIBLE values:

• The minimum Oracle Database release supported for direct upgrade is Oracle Database 19c (19.0.0).

  Before upgrading to Oracle AI Database, you must set the COMPATIBLE initialization parameter to at least 19.0.0, which is the minimum compatible setting for Oracle AI Database.

• In Oracle Real Application Clusters (Oracle RAC) environments, each Oracle Database instance in the Oracle RAC cluster must run with the same COMPATIBLE setting.

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

  SQL> ALTER SYSTEM SET COMPATIBLE = '23.6.0' SCOPE=SPFILE;

  Oracle strongly recommends that you only use three decimals in your COMPATIBLE setting.

• After you increase the COMPATIBLE parameter, you cannot downgrade the database, and you cannot flash back to restore points.

Caution:

Oracle recommends that you only raise the COMPATIBLE parameter to the current release level after you have thoroughly tested the upgraded database.

After the COMPATIBLE parameter has been increased, be aware that downgrade to your earlier release can be unsupported, even though upgrades from that release are supported.

When you plug in an earlier release PDB to a later release CDB where COMPATIBLE is set to a later release than the earlier release PDB, and you upgrade the PDB by using an unplug/plug/upgrade procedure, the COMPATIBLE setting of the upgraded PDB is automatically updated to the COMPATIBLE setting of the later release CDB. The COMPATIBLE setting for PDBs must always be the same setting as CDB$ROOT.

Understanding Oracle Database Compatibility

If new features are incompatible with your earlier release, then updating 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 Oracle AI 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 AI Database

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

Note:

For new installations of Oracle AI Database, COMPATIBLE is set by default in the database to 23.6.0. You cannot change COMPATIBLE to an earlier release. Default behavior for COMPATIBLE settings changes in Oracle AI Database, as described in "Understanding the COMPATIBLE Initialization Parameter"

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

For upgrades from Oracle Database 19c and Oracle Database 21c, if you can provide for an additional maintenance window after your upgrade window, then consider increasing the COMPATIBLE parameter to the new release 7 to 10 days after the upgrade, when you have run your applications on the upgraded system, and are sure that a downgrade is not required. If you do not have an additional maintenance window available, then either raise COMPATIBLE after the upgrade (and lose downgrade capability), or continue to use the earlier release COMPATIBLE setting until you are near a maintenance window, so you have the option of downgrading available to you.

Note:

As a general rule, the value of the COMPATIBLE parameter should not be changed for a Release Update (RU), unless you need to enable new functionality that requires a higher compatible setting. In that case, to use the new functionality available in an RU, update the COMPATIBLE setting to the value major-release.release-update.

Values for the COMPATIBLE Initialization Parameter in Oracle Database

Review to find the default and minimum values for the COMPATIBLE initialization parameter for Oracle AI Database 26ai.

Default and Minimum COMPATIBLE Parameter Values

The minimum supported release for direct upgrade to Oracle AI Database 26ai is Oracle Database 19c. The minimum COMPATIBLE parameter value for Oracle AI Database 26ai is 19.0.0. The default value for the COMPATIBLE parameter is 23.0.0 for Oracle AI Database release updates up to Release Update (RU) 23.6. With RU 23.6, the default compatibility settting is changed to 23.6.0. With RU 23.9, the default compatibility setting is set to 23.9.0.

Before you use a direct upgrade to Oracle AI Database 26ai you must set the COMPATIBLE parameter on your source Oracle Database release to at least 19.0.0.

The COMPATIBLE parameter should not be changed for a Release Update (RU) or Monthly Recommended Patches (MRPs). The following table lists the default and minimum values for the COMPATIBLE parameter in Oracle AI Database 26ai, compared to earlier releases supported for direct upgrade:

Caution:

By default, new database installations for Oracle AI Database 26ai Release Update 23.6 and later updates set compatibility to 23.6.0, and with RU 23.9.0 and later updates, the default is set to 23.9.0.

After the COMPATIBLE parameter is increased, database downgrade is not possible.

When you plug in an earlier release PDB to a later release CDB where COMPATIBLE is set to a later release than the earlier release PDB, and you upgrade the PDB by using an unplug/plug/upgrade procedure, the COMPATIBILE setting of the upgraded PDB is automatically increased to the COMPATIBLE setting of the later release CDB.

Do not alter the COMPATIBLE parameter to a value other than a default release value. Use only one of the default values listed in the following table.

Table 1-2 The COMPATIBLE Initialization Parameter

Oracle Database Release	Default Value	Minimum Value
Oracle AI Database 26ai	23.9.0	19.0.0
Oracle Database 21c	21.0.0	12.2.0
Oracle Database 19c	19.0.0	11.2.0
Oracle Database 18c	18.0.0	11.2.0
Oracle Database 12c Release 2 (12.2)	12.2.0	11.2.0

About Downgrading and Compatibility for Upgrading Oracle Database

Before upgrading to Oracle AI Database 26ai, you must set the COMPATIBLE initialization parameter to at least 19.0.0.

After upgrading or patching to Oracle AI Database, 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 AI Database features are available while the COMPATIBLE initialization parameter is set to a lower value.

Caution:

After you increase the COMPATIBLE parameter to the current release, the database cannot be downgraded to an earlier release. With new installations of Oracle AI Database, the default COMPATIBLE parameter setting is 23.6.0.

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 AI Database database with the COMPATIBLE initialization parameter set to 19.0.0, then the database software generates database structures on disk that are compatible with Oracle Database Release 19c. 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, some new features are enabled that do not create changes on disk that are incompatible with Oracle Database 19c.

• If you make changes to the database that make the database incompatible with the COMPATIBLE initialization parameter setting for the database, then the database does not start, and initialization terminates in an error. To resolve this issue, set the COMPATIBLE initialization parameter to a value that is equivalent to the setting required for the changes that you made.