Working with CDBs in RDS for Oracle

In the Oracle multitenant architecture, a container database (CDB) can include customer-created pluggable databases (PDBs). For more information about CDBs, see Introduction to the Multitenant Architecture in the Oracle Database documentation.

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. A CDB differs from a non-CDB because it can contain pluggable databases (PDBs). A PDB is a portable collection of schemas and objects that appears to an application as a separate database.

Starting with Oracle Database 21c, all databases are CDBs. If your DB instance runs Oracle Database 19c, you can create either a CDB or a non-CDB. A non-CDB uses the traditional Oracle database architecture and can't contain PDBs. You can convert an Oracle Database 19c non-CDB to a CDB, but you can't convert a CDB to a non-CDB. You can only upgrade a CDB to a CDB.

Single-tenant configuration

RDS for Oracle supports the single-tenant configuration of the Oracle multitenant architecture. This means that an RDS for Oracle DB instance can contain only one PDB. You name the PDB when you create your DB instance. The CDB name defaults to RDSCDB and can't be changed.

In RDS for Oracle, your client application interacts with the PDB rather than the CDB. Your experience with a PDB is mostly identical to your experience with a non-CDB. You use the same Amazon RDS APIs in the single-tenant configuration as you do in the non-CDB architecture. You can't access the CDB itself.

Creation and conversion options in a CDB

Although Oracle Database 21c supports only CDBs, Oracle Database 19c supports both CDBs and non-CDBs. The following table shows the different options for creating and converting CDBs and non-CDBs.

As shown in the preceding table, you can't directly upgrade a non-CDB to a CDB in a new major 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.

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:

You specify parameters at the CDB level rather than the PDB level. The PDB inherits parameter settings from the CDB. For more information about setting parameters, see Working with parameter groups. For best practices, see Working with DB parameter groups.

PDB portability in a CDB

Your CDB can contain only a single PDB. You can't unplug this PDB or plug in a different PDB. 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.

Configuring an RDS for Oracle CDB

Configuring a CDB is similar to configuring a non-CDB.

Creating an RDS for Oracle CDB instance

In RDS for Oracle, creating a CDB is almost identical to creating a non-CDB. The difference is that you choose the Multitenant architecture when creating your DB instance. To create a CDB, use the Amazon Web Services Management Console, the Amazon CLI, or the RDS API.

aws rds create-db-instance \
    --engine oracle-ee-cdb \
    --db-instance-identifier my-cdb-inst \
    --db-name mypdb \
    --allocated-storage 250 \
    --db-instance-class db.t3.large \
    --master-username pdb_admin \
    --master-user-password masteruserpassword \
    --backup-retention-period 3

aws rds create-db-instance ^
    --engine oracle-ee-cdb ^
    --db-instance-identifier my-cdb-inst ^
    --db-name mypdb ^
    --allocated-storage 250 ^
    --db-instance-class db.t3.large ^
    --master-username pdb_admin ^
    --master-user-password masteruserpassword ^
    --backup-retention-period 3

{
    "DBInstance": {
        "DBInstanceIdentifier": "my-cdb-inst",
        "DBInstanceClass": "db.t3.large",
        "Engine": "oracle-ee-cdb",
        "DBInstanceStatus": "creating",
        "MasterUsername": "pdb_user",
        "DBName": "MYPDB",
        "AllocatedStorage": 250,
        "PreferredBackupWindow": "04:59-05:29",
        "BackupRetentionPeriod": 3,
        "DBSecurityGroups": [],
        "VpcSecurityGroups": [
            {
                "VpcSecurityGroupId": "sg-0a2bcd3e",
                "Status": "active"
            }
        ],
        "DBParameterGroups": [
            {
                "DBParameterGroupName": "default.oracle-ee-cdb-19",
                "ParameterApplyStatus": "in-sync"
            }
        ],
        "DBSubnetGroup": {
            "DBSubnetGroupName": "default",
            "DBSubnetGroupDescription": "default",
            "VpcId": "vpc-1234567a",
            "SubnetGroupStatus": "Complete",
            ...

Connecting to a PDB in your RDS for Oracle CDB

You can use a utility like SQL*Plus to connect to a PDB. To download Oracle Instant Client, which includes a standalone version of SQL*Plus, see Oracle Instant Client Downloads.

To connect SQL*Plus to your PDB, you need the following information:

For information about finding the preceding information, see Finding the endpoint of your RDS for Oracle DB instance.

sqlplus 'master_user_name@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=endpoint)(PORT=port))(CONNECT_DATA=(SID=pdb_name)))'

sqlplus master_user_name@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=endpoint)(PORT=port))(CONNECT_DATA=(SID=pdb_name)))

SQL*Plus: Release 19.0.0.0.0 Production on Mon Aug 21 09:42:20 2021

SQL>

Backing up and restoring a CDB

DB snapshots work the same way in the multitenant and non-multitenant architecture. The only difference is that when you restore a DB snapshot, you can only rename the PDB, not the CDB. The CDB is always named RDSCDB. For more information, see Oracle Database considerations.

Converting an RDS for Oracle non-CDB to a CDB

You can change the architecture of an Oracle database from the traditional non-CDB architecture to the multitenant architecture. When you upgrade your database engine version, you can't change the database architecture in the same operation. Therefore, to upgrade an Oracle Database 19c non-CDB to an Oracle Database 21c CDB, you first need to convert the non-CDB to a CDB, and then upgrade the 19c CDB to a 21c CDB.

The non-CDB conversion operation has the following requirements:

The operation has the following limitations:

aws rds modify-db-instance \
    --db-instance-identifier my-non-cdb \
    --engine oracle-ee-cdb \
    --option-group-name custom-option-group \
    --db-parameter-group-name custom-parameter-group

aws rds modify-db-instance ^
    --db-instance-identifier my-non-cdb ^
    --engine oracle-ee-cdb ^
    --option-group-name custom-option-group ^
    --db-parameter-group-name custom-parameter-group

Upgrading your CDB

You can upgrade a CDB to a different Oracle Database release. For example, you can upgrade an Oracle Database 19c CDB to an Oracle Database 21c CDB. You can't change the database architecture during an upgrade. Thus, you can't upgrade a non-CDB to a CDB or upgrade a CDB to a non-CDB.

The procedure for upgrading a CDB to a CDB is the same as for upgrading a non-CDB to a non-CDB. For more information, see Upgrading the RDS for Oracle DB engine.