Overview of RDS for Oracle CDBs - Amazon Relational Database Service
Multi-tenant configuration of the CDB architectureSingle-tenant configuration of the CDB architectureCreation and conversion options for CDBsUser accounts and privilegesParameter group familiesLimitations of RDS for Oracle CDBs

Overview of RDS for Oracle CDBs

You can create an RDS for Oracle DB instance as a container database (CDB) when you run Oracle Database 19c or higher. Starting with Oracle Database 21c, all databases are CDBs. A CDB differs from a non-CDB because it can contain pluggable databases (PDBs), which are called tenant databases in RDS for Oracle. A PDB is a portable collection of schemas and objects that appears to an application as a separate database.

You create your initial tenant database (PDB) when you create your CDB instance. In RDS for Oracle, your client application interacts with a PDB rather than the CDB. Your experience with a PDB is mostly identical to your experience with a non-CDB.

Multi-tenant configuration of the CDB architecture

RDS for Oracle supports the multi-tenant configuration of the Oracle multitenant architecture, also called the CDB architecture. In this configuration, your RDS for Oracle CDB instance can contain 1–30 tenant databases, depending on the database edition and any required option licenses. In Oracle database, a tenant database is a PDB. Your DB instance must use Oracle database release 19.0.0.0.ru-2022-01.rur-2022.r1 or higher.

Note

The Amazon RDS feature is called "multi-tenant" rather than "multitenant" because it is a capability of the RDS platform, not just the Oracle DB engine. The term "Oracle multitenant" refers exclusively to the Oracle database architecture, which is compatible with both on-premises and RDS deployments.

You can configure the following settings:

  • Tenant database name

  • Tenant database master username

  • Tenant database master password

  • Tenant database character set

  • Tenant database national character set

The tenant database character set can be different from the CDB character set. The same applies to the national character set. After you create your initial tenant database, you can create, modify, or delete tenant databases using RDS APIs. The CDB name defaults to RDSCDB and can't be changed. For more information, see Settings for DB instances and Modifying an RDS for Oracle tenant database.

Single-tenant configuration of the CDB architecture

RDS for Oracle supports a legacy configuration of the Oracle multitenant architecture called the single-tenant configuration. In this configuration, an RDS for Oracle CDB instance can contain only one tenant (PDB). You can't create more PDBs later.

Creation and conversion options for CDBs

Oracle Database 21c supports only CDBs, whereas Oracle Database 19c supports both CDBs and non-CDBs. All RDS for Oracle CDB instances support both the multi-tenant and single-tenant configurations.

Creation, conversion, and upgrade options for the Oracle database architecture

The following table shows the different architecture options for creating and upgrading RDS for Oracle databases.

Release Database creation options Architecture conversion options Major version upgrade targets
Oracle Database 21c CDB architecture only N/A N/A
Oracle Database 19c CDB or non-CDB architecture Non-CDB to CDB architecture (April 2021 RU or higher) Oracle Database 21c CDB

As shown in the preceding table, you can't directly upgrade a non-CDB to a CDB in a new major database version. But you can convert an Oracle Database 19c non-CDB to an Oracle Database 19c CDB, and then upgrade the Oracle Database 19c CDB to an Oracle Database 21c CDB. For more information, see Converting an RDS for Oracle non-CDB to a CDB.

Conversion options for CDB architecture configurations

The following table shows the different options for converting the architecture configuration of an RDS for Oracle DB instance.

Current architecture and configuration Conversion to the single-tenant configuration of the CDB architecture Conversion to the multi-tenant configuration of the CDB architecture Conversion to the non-CDB architecture
Non-CDB Supported Supported* N/A
CDB using the single-tenant configuration N/A Supported Not supported
CDB using the multi-tenant configuration Not supported N/A Not supported

* You can't convert a non-CDB to the multi-tenant configuration in a single operation. When you convert a non-CDB to a CDB, the CDB is in the single-tenant configuration. You can then convert the single-tenant to the multi-tenant configuration in a separate operation.

User accounts and privileges in a CDB

In the Oracle multitenant architecture, all user accounts are either common users or local users. A CDB common user is a database user whose single identity and password are known in the CDB root and in every existing and future PDB. In contrast, a local user exists only in a single PDB.

The RDS master user is a local user account in the PDB, which you name when you create your DB instance. If you create new user accounts, these users will also be local users residing in the PDB. You can't use any user accounts to create new PDBs or modify the state of the existing PDB.

The rdsadmin user is a common user account. You can run RDS for Oracle packages that exist in this account, but you can't log in as rdsadmin. For more information, see About Common Users and Local Users in the Oracle documentation.

Parameter group families in a CDB

CDBs have their own parameter group families and default parameter values. The CDB parameter group families are as follows:

  • oracle-ee-cdb-21

  • oracle-se2-cdb-21

  • oracle-ee-cdb-19

  • oracle-se2-cdb-19

Limitations of RDS for Oracle CDBs

RDS for Oracle supports a subset of features available in an on-premises CDB.

CDB limitations

The following limitations apply to RDS for Oracle at the CDB level:

  • You can’t connect to a CDB. You always connect to the tenant database (PDB) rather than the CDB. Specify the endpoint for the PDB just as for a non-CDB. The only difference is that you specify pdb_name for the database name, where pdb_name is the name you chose for your PDB.

  • You can't convert a CDB in the multi-tenant configuration to a CDB in the single-tenant conversion. Conversion to the multi-tenant configuration is one-way and irreversible.

  • You can't enable or convert to the multi-tenant configuration if your DB instance uses an Oracle database release lower than 19.0.0.0.ru-2022-01.rur-2022.r1.

  • You can't use an RDS for Oracle CDB with ORDS 22 and higher. As a workaround, you can either use a lower version of ORDS or use an Oracle Database 19c non-CDB.

  • You can't use Oracle Data Guard in the multi-tenant configuration, but you can use it in the single-tenant configuration.

  • You can't use Database Activity Streams in a CDB.

  • You can enable auditing from within CDB$ROOT. You must enable auditing within each PDB individually.

Tenant database (PDB) limitations

The following limitations apply to tenant databases in the RDS for Oracle multi-tenant configuration:

  • You can't defer tenant database operations to the maintenance window. All changes occur immediately.

  • You can't add a tenant database to a CDB that uses the single-tenant configuration.

  • You can't add or modify multiple tenant databases in a single operation. You can only add or modify them one at a time.

  • You can't modify a tenant database to be named CDB$ROOT or PDB$SEED.

  • You can't delete a tenant database if it is the only tenant in the CDB.

  • Not all DB instance class types have sufficient resources to support multiple PDBs in an RDS for Oracle CDB instance. An increased PDB count affects the performance and stability of the smaller instance classes and increases the time of most instance-level operations, for example, database upgrades.

  • You can't use multiple AWS accounts to create PDBs in the same CDB. PDBs must be owned by the same account as the DB instance that the PDBs are hosted on.

  • All PDBs in a CDB use the same endpoint and database listener.

  • The following operations aren't supported at the PDB level but are supported at the CDB level:

    • Backup and recovery

    • Database upgrades

    • Maintenance actions

  • The following features aren't supported at the PDB level but are supported at the CDB level:

    • Option groups (options are installed on all PDBs on your CDB instance)

    • Parameter groups (all parameters are derived from the parameter group associated with your CDB instance)

  • PDB-level operations that are supported in the on-premises CDB architecture but aren't supported in an RDS for Oracle CDB include the following:

    Note

    The following list is not exhaustive.

    • Application PDBs

    • Proxy PDBs

    • Starting and stopping a PDB

    • Unplugging and plugging in PDBs

      To move data into or out of your CDB, use the same techniques as for a non-CDB. For more information about migrating data, see Importing data into Oracle on Amazon RDS.

    • Setting options at the PDB level

      The PDB inherits options settings from the CDB option group. For more information about setting options, see Parameter groups for Amazon RDS. For best practices, see Working with DB parameter groups.

    • Configuring parameters in a PDB

      The PDB inherits parameter settings from the CDB. For more information about setting option, see Adding options to Oracle DB instances.

    • Configuring different listeners for PDBs in the same CDB

    • Oracle Flashback features