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Migrating On-Premises Databases to the Cloud Limitations

Overview

Purpose

This tutorial covers some of the limitations encountered when migrating on-premises databases to the Oracle Cloud Database Service.

Time to Complete

Approximately 15 minutes.

Introduction

In this tutorial, you discover the limitations when exporting an on-premises database holding encrypted data by using the Transportable Tablespace mode (TTS), or when unplugging an on-premises PDB with a COMPATIBLE value different than the value of the DBaaS CDB into which the plugging will occur.

Prerequisites

Before starting this tutorial, it may be helpful to have followed the Signing Up for a Database Cloud Service, Connecting to a Database Cloud Service (DBaaS) Instance Through an SSH Tunnel and Creating a Database Cloud Service (DBaaS) Instance tutorials.

TTS Export and Encrypted Data


You can use Oracle Data Pump to move an on-premises 11g non-CDB to an 11g DBaaS database (non-CDB), or an on-premises 12c non-CDB or PDB  to a 12c DBaaS database (non-CDB or new PDB or existing PDB).

In this particular case, you decide to move the USERS tablespace of the PDB1 on-premises 12c PDB to the PDB2 of the 12c DBaaS ORCL CDB.

  1. Set your session environment to the PDB1 on-premises 12c PDB. The PDB is contained into the cdb2 CDB.

  2. You want to perform the operation with Data Pump export in TTS mode. To perform the TTS export, you need to set the tablespace in READ ONLY mode.

  3. Export the USERS tablespace of the PDB1 on-premises 12c PDB in TTS mode.
    Remark: Passwords are blurred due to security rules.


  4. Note: Observe that the operation fails because the tablespace has encrypted columns and this operation type is not supported.

  5. Export the USERS tablespace of the PDB1 on-premises 12c PDB in conventional mode.
    Remark: File location is blurred and refer to ORCL subdirectory.



    Note: Observe that the operation succeeded because the tablespace is exported with the conventional mode.

    Be aware of the warning message telling you that encrypted data has been stored unencrypted in the dump file set. While the export takes place in a conventional mode, encrypted data is selected and read and therefore unencrypted.
    You can use Data Pump export parameters to ensure that the data is reencrypted in the dump file.
    6.  

  6. Set your session environment to the 12c DBaaS ORCL CDB.

  7. Import the USERS tablespace in PDB2  of the 12c DBaaS ORCL CDB using the conventional mode. You will be prompted to provide the password used during the export, to decrypt the encrypted data from the dump file and then reencrypt it into the database.

Unplugging and Plugging and COMPATIBLE


To plug an unplugged on-premises PDB in a DBaaS CDB, customers need to be aware of the COMPATIBLE initialization parameter as this is the constraining factor for the general possibility of unplug/plug. The database release tells if you have to run the upgrade or downgrade procedure.

Run the DBMS_PDB.CHECK_PLUG_COMPATIBILITY function to determine whether the on-premises unplugged PDB is compatible with the DBaaS CDB.
  1. In this case, you decide to migrate the PDB_CDB2 on-premises PDB to the 12c ORCL DBaaS CDB.
    Connect to the PDB_CDB2 on-premises PDB. You will check if the PDB is compatible with the 12c ORCL DBaaS CDB before unplugging.



  2. Generate the XML file that provides the list of objects (tablespaces, data files, parameters...) of the PDB_CDB2 on-premises PDB that will be used during the plugging operation.



    If the database uses 2.02 GB of storage, it is allocated 2.10 GB.

  3. Connect to the 12c ORCL DBaaS CDB.



  4. Run the DBMS_PDB.CHECK_PLUG_COMPATIBILITY function to determine whether the PDB_CDB2 on-premises PDB is compatible with the 12c ORCL DBaaS CDB. Use the XML file generated in step 2.



  5. There are some incompatibilities. Notice that the COMPATIBLE value of the PDB_CDB2 on-premises PDB is NOT compatible with the 12c ORCL DBaaS CDB value.


    Some of the actions need to be implemented such as when PDB's version does not match CDB's version. This is the case here, mentioned in the first row. The solution is mentioned: Either upgrade the PDB or reload the components in the PDB. Another action which prevents the PDB to be opened is the COMPATIBLE parameter mismatch. It is mentioned in the 3rd row. You have to adjust the COMPATIBLE parameter value.
    Other actions are warnings only such as instance parameters values like SGA_TARGET or PGA_AGGREGATE_TARGET. You can open the PDB without intervention.

Summary

    You must be aware of limitations when migrating on-premises  databases to the Cloud and using different methods such as Data Pump export and import, unplug and plug, or RMAN.
    In this tutorial, you learned to:

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