ApsaraDB for OceanBase:Migrate data from an Oracle tenant of OceanBase Database to an Oracle database

Background

In the ApsaraDB for OceanBase console, you can create a project to migrate data from an Oracle tenant of OceanBase Database to an Oracle database. You can seamlessly migrate existing and incremental business data from the source database to the destination Oracle database through schema migration, full migration, and incremental synchronization.

The data transmission service also allows you to aggregate data of multiple tables in the source database to the same table in the destination database through full migration and incremental synchronization without the need for schema migration. The aggregation and synchronization feature has the following limitations:

• For full migration and incremental synchronization, the destination table must contain all columns that exist in the source table. Otherwise, the data transmission service returns an error.

• The source table must contain a primary key column.

• The destination table can contain a column that does not exist in the source table.

Prerequisites

• The data transmission service has the privilege to access cloud resources. For more information, see Grant privileges to roles for data transmission.

• You have created the corresponding schema in the destination Oracle database.

• You have created dedicated database users in the source Oracle tenant of OceanBase Database and the destination Oracle database for data migration and granted the corresponding privileges to the users. For more information, see Create a database user.

• You have created the __OCEANBASE_INNER_DRC_USER user in the corresponding tenant and granted the required privileges to the user before migration, if you want to migrate a table without a primary key. For more information, see Create the __oceanbase_inner_drc_user user.

Limitations

• Limitations on the source database

  Do not perform DDL operations for database or schema changes during schema migration or full data migration. Otherwise, the data migration project may be interrupted.

• The data transmission service supports the following Oracle database versions: 10g, 11g, 12c, 18c, and 19c. Version 12c and later provide container databases (CDBs) and pluggable databases (PDBs).

• The data transmission service does not support the incremental synchronization of a table if all columns in the table are of the following three large object (LOB) types: BLOB, CLOB, and NCLOB.

• The data transmission service does not support the migration of a non-template-based subpartitioned table in an Oracle tenant of OceanBase Database to an Oracle database.

• The data transmission service does not support expression-based indexes.

• The data transmission service supports the aggregation of only tables with a primary key.

• The data transmission service supports the migration of only objects whose database name, table name, and column name are ASCII-encoded without special characters. The special characters are line breaks, spaces, and the following characters: . | " ' ` ( ) = ; / &

• If the destination is a database, the data transmission service does not support triggers in the destination database. If triggers exist in the destination database, the data migration may fail.

• Data source identifiers and user accounts must be globally unique in the data transmission system. ​

• The data transmission service can parse up to 5 TB of incremental logs of Oracle databases per day.

• You cannot create a database object whose name exceeds 30 bytes in length in an Oracle database of version 11g or earlier. When you migrate data from an Oracle tenant of OceanBase Database to an Oracle database, do not create objects whose names are more than 30 bytes in length in the source database.

• By default, the data transmission service does not support the reverse incremental migration of database objects, such as schemas, tables, and columns, whose name exceeds 30 bytes in length from an Oracle tenant of OceanBase Database to an Oracle database of version 12c or later. To migrate database objects whose name exceeds 30 bytes in length, contact OceanBase Technical Support.

• During reverse incremental migration from an Oracle tenant of OceanBase Database to an Oracle database, the data transmission service does not support the execution of certain UPDATE statements in the Oracle database. The following example shows an unsupported UPDATE statement:

  UPDATE TABLE_NAME SET KEY=KEY+1;

  In the preceding statement, TABLE_NAME specifies the table name and KEY is a column of the NUMERIC type that is defined as the primary key column.

Considerations

• When you perform incremental synchronization for an Oracle database, we recommend that you make sure that each archive file is less than 2 GB in size in the Oracle database.

• Archive files must be stored for more than two days in the Oracle database. Otherwise, in the case of a sharp increase in the number of archive files, restore may fail due to the lack of required archive files.

• If you use OceanBase Database V4.x, we recommend that you enable log archiving. After log archiving is enabled, if clogs are recycled, the data transmission service can still implement incremental synchronization by consuming archive logs.

• If a table does not have a primary key but contains data of the LOB type, the reverse incremental migration of the table can suffer poor data quality.

• If the UTF-8 character set is used in the source, we recommend that you use a compatible character set, such as UTF-8 or UTF-16, in the destination to avoid garbled characters.

• If the clocks between nodes or between the client and the server are out of synchronization, the latency may be inaccurate during incremental synchronization or reverse incremental migration.

  For example, if the clock is earlier than the standard time, the latency can be negative. If the clock is later than the standard time, the latency can be positive.

• When the Oracle database and the Oracle tenant of OceanBase Database use different character sets, the field length varies based on the type of the data migration project.

• To migrate data from a table without a primary key, you must add a hidden column to the destination table. However, if the version of the destination Oracle database is earlier than 12c, you must add a non-hidden column to the destination table.

• If the source table contains the field name OMS_PK_INCRMT, the incremental synchronization task is interrupted and cannot be resumed.

• If you modify a unique index at the destination when DDL synchronization is disabled, you must restart the data migration project to avoid data inconsistency.

• If forward switchover is disabled for a data migration project, delete the unique indexes and pseudocolumns from the destination. If you do not delete the unique indexes and pseudocolumns, data cannot be written, and pseudocolumns are generated again when data is imported to the downstream system, causing conflicts with the pseudocolumns in the source.

  If forward switchover is enabled for the data migration project, the data transmission service automatically deletes the hidden column and unique index based on the type of the migration project. For more information, see Mechanisms for handling hidden columns.

• Take note of the following items if you want to aggregate multiple tables:

  • We recommend that you configure the mappings between the source and destination databases by importing objects or specifying matching rules.

  • We recommend that you manually create schemas at the destination. If you create a schema by using the data transmission service, skip the failed objects in the schema migration step.

• Check the objects in the recycle bin of the Oracle tenant of OceanBase Database. If the recycle bin contains more than 100 objects, internal table queries may time out. You must clear the objects in the recycle bin.

  • Query whether the recycle bin is enabled.

  SELECT Value FROM V$parameter WHERE Name = 'recyclebin';

  • Query the number of objects in the recycle bin.

  SELECT count(*) FROM RECYCLEBIN;

• If you skip the database ROW_MOVEMENT check for the source primary database during migration, data inconsistency may occur when you synchronize tables whose ROW_MOVEMENT value is set to enable.

• In a data migration project where the source is an OceanBase database and DDL synchronization is enabled, if a RENAME operation is performed on a table in the source, we recommend that you restart the project to avoid data loss during incremental synchronization.

Supported source and destination instance types

In the following table, OB_Oracle stands for an Oracle tenant of OceanBase Database.

Data type mappings

Create a data migration project

1. Log on to the ApsaraDB for OceanBase console and purchase a data migration project.

   For more information, see Purchase a data migration project.

2. Choose Data Transmission > Data Migration. On the page that appears, click Configure for the data migration project.

   

   If you want to reference the configurations of an existing project, click Reference Configuration. For more information, see Reference and clear data migration project configurations.

3. On the Select Source and Destination page, configure the parameters.

   

   Parameter	Description
   Migration Project Name	We recommend that you set it to a combination of digits and letters. It must not contain any spaces and cannot exceed 64 characters in length.
   Tag (Optional)	Click the field and select a target tag from the drop-down list. You can also click Manage Tags to create, modify, and delete tags. For more information, see Use tags to manage data migration projects.
   Source	If you have created an Oracle tenant in OceanBase Database as a data source, select it from the drop-down list. Otherwise, click New Data Source in the drop-down list to create one in the dialog box on the right side. For more information about the parameters, see Create an OceanBase data source. Important For an Oracle tenant of OceanBase Database, Instance Type must be set to OceanBase Cluster Instance.
   Destination	If you have created an Oracle data source, select it from the drop-down list. Otherwise, click New Data Source in the drop-down list to create one in the dialog box on the right side. For more information about the parameters, see Create an Oracle data source.

4. Click Next. On the Select Migration Type page, specify migration types for the current data migration project.

   Valid values of Migration Type are Schema Migration, Full Migration, Incremental Synchronization, Full Verification, and Reverse Incremental Migration.

   

   Migration type	Description
   Schema migration	After a schema migration task is started, the data transmission service migrates the definitions of database objects (such as tables, indexes, constraints, comments, and views) from the source database to the destination database and automatically filters out temporary tables.
   Full migration	After a full migration task is started, the data transmission service migrates existing data of tables in the source database to corresponding tables in the destination database. If you select Full Migration, we recommend that you collect the statistics of the Oracle tenant of OceanBase Database before the data migration.
   Incremental synchronization	After an incremental synchronization task is started, the data transmission service synchronizes changed data (data that is added, modified, or removed) from the source database to corresponding tables in the destination database. Options for Incremental Synchronization are DML Synchronization and DDL Synchronization. You can select the operations as needed. For more information about DDL synchronization, see DDL synchronization from an Oracle tenant of OceanBase Database to an Oracle database. Incremental Synchronization has the following limitations: If you select DDL Synchronization, when you perform a DDL operation for synchronization that is not supported by the data transmission service in the source database, data migration may fail. If the DDL operation is ADD COLUMN, we recommend that you set the column to a NULL column. Otherwise, data migration may be interrupted.
   Full verification	After the full migration and incremental synchronization tasks are completed, the data transmission service automatically initiates a full verification task to verify the tables in the source and destination databases. If you select Full Verification, we recommend that you collect the statistics of the Oracle tenant of OceanBase Database and use the GATHER_SCHEMA_STATS or GATHER_TABLE_STATS statement to collect the statistics of the Oracle database before full verification. If you have selected Incremental Synchronization but did not select all DML statements in the DML Synchronization section, the data transmission service does not support full verification.
   Reverse incremental migration	Data changes made in the destination database after the business database switchover are applied to the source database in real time. Note This feature is available for a limited-time free trial.

5. Click Next. On the Select Migration Objects page, specify the migration objects for the data migration project.

   You can select Specify Objects or Match Rules to specify the migration objects.

   Important

   • The names of tables to be migrated, as well as the names of columns in the tables, must not contain Chinese characters.

   • If a database or table name contains double dollar signs ($$), you cannot create the migration project.

   • After you specify the migration objects by using the Specify Objects option, the DDL operations take effect only for the selected objects, and table creation is not supported.

   • If you select Specify Objects, select the objects to be migrated on the left and click > to add them to the list on the right. You can select tables and views of one or more databases as the migration objects.

     The data transmission service allows you to import objects from text files, rename destination objects, set row filters, view column information, and remove a single migration object or all migration objects.

     

     Operation	Description
     Import Objects	In the list on the right, click Import Objects in the upper-right corner. In the dialog box that appears, click OK. Important This operation will overwrite previous selections. Proceed with caution. In the Import Objects dialog box, import the objects to be migrated. You can import CSV files to rename databases or tables and set row filtering conditions. For more information, see Download and import settings of migration objects. Click Validate. After you import the migration objects, check their validity. Column field mapping is not supported. After the validation succeeds, click OK.
     Rename	The data transmission service allows you to rename migration objects. For more information, see Rename a database table.
     Settings	The data transmission service allows you to filter rows by using WHERE conditions. For more information, see Use SQL conditions to filter data. You can also view column information of the migration objects in the View Columns section.
     Remove/Remove All	The data transmission service allows you to remove a single object or all migration objects that are added to the right-side list during data mapping. Remove a single migration object In the list on the right, move the pointer over the object that you want to remove, and click Remove to remove the migration object. Remove all migration objects In the list on the right, click Remove All in the upper-right corner. In the dialog box that appears, click OK to remove all migration objects.

   • Select Match Rules. For more information, see Configure matching rules.

6. Click Next. On the Migration Options page, configure the parameters.

   

   Parameter	Description
   Incremental Synchronization Start Timestamp	If you have specified the Full Migration migration type, this parameter is not displayed. If you have selected Incremental Synchronization but not Full Migration, specify a point in time after which the data is to be synchronized. The default value is the current system time. For more information, see Set an incremental synchronization timestamp.
   Processing Strategy When Destination Table Has Records	The processing strategy adopted when a destination table contains records. This parameter is displayed only when Full Migration is selected on the Select Migration Type page. Valid values: Ignore and Stop Migration. If you select Ignore, when the data to be inserted conflicts with the existing data of a destination table, the data transmission service retains the existing data and records the conflict data. Important If you select Ignore, data is pulled by using the IN mode during full verification. In this case, verification is inapplicable if the destination has a large amount of data, and the verification performance is downgraded. If you select Stop Migration and a destination table contains records, an error prompting migration unsupported is reported during full migration. In this case, you must process the data in the destination table and then continue with the migration. Important If you click Resume in the dialog box prompting the error, the data transmission service ignores this error and continues to migrate data. Proceed with caution.
   Whether to Allow Post-indexing	Specifies whether to create indexes after the full migration is completed. Post-indexing can shorten the time required for full migration. For more information about the considerations on post-indexing, see the description below. Important This parameter is displayed only if both Schema Migration and Full Migration are selected on the Select Migration Type page. Only non-unique key indexes can be created after the migration is completed.

   If post-indexing is allowed, we recommend that you adjust the parameter settings based on the hardware conditions of OceanBase Database and the business traffic.

   • If you use OceanBase Database V4.x, adjust the settings of the following parameters of the sys tenant and business tenants by using a command-line interface (CLI) client.

     • Adjust the parameter settings of the sys tenant

       // parallel_servers_target specifies the queue condition for parallel queries on each server. 
       // To maximize performance, we recommend that you set this parameter to a value greater than, for example, 1.5 times, the number of physical CPU cores. In addition, make sure that the value does not exceed 64, to prevent database kernels from contending for locks. 
       set global parallel_servers_target = 64; 

     • Adjust the parameter settings of a business tenant

       // Specify the limit on the file memory buffer size.
       alter system set _temporary_file_io_area_size = '10' tenant = 'xxx'; 
       // Disable throttling in V4.x.
       alter system set sys_bkgd_net_percentage = 100;

   • If you use OceanBase Database V3.x, adjust the settings of the following parameters of the sys tenant by using a CLI client.

     // parallel_servers_target specifies the queue condition for parallel queries on each server. 
     // To maximize performance, we recommend that you set this parameter to a value greater than, for example, 1.5 times, the number of physical CPU cores. In addition, make sure that the value does not exceed 64, to prevent database kernels from contending for locks. 
     set global parallel_servers_target = 64; 
     // data_copy_concurrency specifies the maximum number of concurrent data migration and replication tasks allowed in the system. 
     alter system set data_copy_concurrency = 200;

7. Click Precheck to start a precheck on the data migration project.

   During the precheck, the data transmission service checks the read and write privileges of the database users and the network connections of the databases. The data migration project can be started only after it passes all check items. Take note of the following items if an error is returned during the precheck:

   • You can identify and troubleshoot the error and then perform the precheck again.

   • You can also click Skip in the Actions column of the failed precheck item. A dialog box appears, prompting you for the impact. If you want to skip this operation, click OK.

8. After the precheck is passed, click Start Project.

   If you do not need to start the project now, click Save. After that, you can only manually start the project or start it in a batch operation on the Migration Projects page. For more information about batch operations, see Perform batch operations on data migration projects.

   The data transmission service allows you to modify the migration objects when a migration project is running. For more information, see View and modify migration objects. After the data migration project is started, it will be executed based on the selected migration types. For more information, see View migration details.

References

• Create an OceanBase data source

• Create an Oracle data source

• Configure matching rules

• View details of a data migration project