# Oracle major version upgrades
<a name="USER_UpgradeDBInstance.Oracle.Major"></a>

To perform a major version upgrade, modify the DB instance manually. Major version upgrades don't occur automatically. 

**Important**  
Make sure that you thoroughly test any upgrade to verify that your applications work correctly before applying the upgrade to your production databases. For more information, see [Testing an Oracle DB upgrade](USER_UpgradeDBInstance.Oracle.UpgradeTesting.md).

**Topics**
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## Supported versions for major upgrades
](#USER_UpgradeDBInstance.Oracle.Major.supported-versions)
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## Supported instance classes for major upgrades
](#USER_UpgradeDBInstance.Oracle.Major.instance-classes)
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## Gathering statistics before major upgrades
](#USER_UpgradeDBInstance.Oracle.Major.gathering-stats)
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## Allowing major upgrades
](#USER_UpgradeDBInstance.Oracle.Major.allowing-upgrades)

## Supported versions for major upgrades
<a name="USER_UpgradeDBInstance.Oracle.Major.supported-versions"></a>

Amazon RDS supports the following major version upgrades.


****  

| Current version | Upgrade supported | 
| --- | --- | 
|  19.0.0.0 using the CDB architecture  |  21.0.0.0  | 

A major version upgrade of Oracle Database must upgrade to a Release Update (RU) that was released in the same month or later. Major version downgrades aren't supported for any Oracle Database versions.

## Supported instance classes for major upgrades
<a name="USER_UpgradeDBInstance.Oracle.Major.instance-classes"></a>

Your current Oracle DB instance might run on a DB instance class that isn't supported for the version to which you are upgrading. In this case, before you upgrade, migrate the DB instance to a supported DB instance class. For more information about the supported DB instance classes for each version and edition of Amazon RDS for Oracle, see [DB instance classes](Concepts.DBInstanceClass.md).

## Gathering statistics before major upgrades
<a name="USER_UpgradeDBInstance.Oracle.Major.gathering-stats"></a>

Before you perform a major version upgrade, Oracle recommends that you gather optimizer statistics on the DB instance that you are upgrading. This action can reduce DB instance downtime during the upgrade.

To gather optimizer statistics, connect to the DB instance as the master user, and run the `DBMS_STATS.GATHER_DICTIONARY_STATS` procedure, as in the following example.

```
EXEC DBMS_STATS.GATHER_DICTIONARY_STATS;
```

For more information, see [ GATHER\$1DICTIONARY\$1STATS Procedure](https://docs.oracle.com/en/database/oracle/oracle-database/19/arpls/DBMS_STATS.html?source=%3Aso%3Atw%3Aor%3Aawr%3Aodv%3A%3A#GUID-867989C7-ADFC-4464-8981-437CEA7F331E) in the Oracle documentation.

## Allowing major upgrades
<a name="USER_UpgradeDBInstance.Oracle.Major.allowing-upgrades"></a>

A major engine version upgrade might be incompatible with your application. The upgrade is irreversible. If you specify a major version for the EngineVersion parameter that is different from the current major version, you must allow major version upgrades.

If you upgrade a major version using the CLI command [modify-db-instance](https://docs.aws.amazon.com/cli/latest/reference/rds/modify-db-instance.html), specify `--allow-major-version-upgrade`. This setting isn't persistent, so you must specify `--allow-major-version-upgrade` whenever you perform a major upgrade. This parameter has no impact on upgrades of minor engine versions. For more information, see [Upgrading a DB instance engine version](USER_UpgradeDBInstance.Upgrading.md).

If you upgrade a major version using the console, you don't need to choose an option to allow the upgrade. Instead, the console displays a warning that major upgrades are irreversible.