Migrate data from an Oracle tenant of OceanBase Database to an Oracle database

Background

In the ApsaraDB for OceanBase console, you can create a task 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 target 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 target database through full migration and incremental synchronization without schema migration. The merging and synchronization feature has the following limitations:

• For full migration and incremental synchronization, the target 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 target 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 target Oracle database.

• You have created dedicated database users in the source Oracle tenant of OceanBase Database and the target Oracle database for data migration, and granted the required 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 that modify database or table schemas during schema migration or full migration. Otherwise, the data migration task may be interrupted.

• The data transmission service supports Oracle 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 an object only when the following conditions are met: the database name, table name, and column name of the object are ASCII-encoded without special characters. The special characters are line breaks, spaces, and the following characters: . | " ' ` ( ) = ; / & \.

• The data transmission service does not support triggers in the target database. If triggers exist in the target database, the data migration may fail.

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

• 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 an object with a name exceeding 30 bytes in length in the source database.

• The data transmission service does not support the migration of spatial indexes, including existing spatial indexes and new spatial indexes generated by the INSERT INTO USER_SDO_GEOM_METADATA operation during incremental synchronization.

• Take note of the following limitations on GIS data supported in an Oracle database:

  • Data with the spatial reference identifiers (SRIDs) of 0, 4327, and 4328 is not supported.

  • Data that will be converted into the scientific notation format by the get_wkt operation, such as SDO_POINT_TYPE(0.00001, 0.00001, 0), is not supported.

  • Only data with the coordinates ranging from -2147483647 to 2147483647 is supported.

  • When you use EPSG:4326, make sure that the longitude value ranges from -180 to 180 and the latitude value ranges from -90 to 90. Otherwise, data inconsistency may occur during the data migration.

  • Data with the number of digits on the right of the decimal point exceeding the maximum number allowed is not supported. This is because the read data in the scientific notation format cannot be written to an Oracle database.

    The read data in the scientific notation format is defined by two concepts:

    • scale: indicates the number of decimal places in a value. For example, 123.45 has a scale of 2, and 0.000001 has a scale of 6.

    • precision: indicates the precision of the data, which is the number of digits starting from the first non-zero digit in the data. For example, 123.45 has a precision of 5, and 0.000001 has a precision of 1.

    If -scale + (precision +1) is less than -2, the data is converted into data in the scientific notation format with the base of 10.

    For example, 0.00001 has a scale of 5 and a precision of 1, and is converted into 1e-5e because -5 + (1 + 1) is equal to -3, which is less than -2. The specific value is obtained by the sdo_geometry.get_wkt() or SDO_UTIL.TO_WKTGEOMETRY method.

  • Data with a value greater than the maximum 32-bit integer (2147483647) or less than the minimum 32-bit integer (-2147483647) is not supported.

Considerations

• Take note of the following considerations for reverse incremental synchronization from an Oracle tenant of OceanBase Database to an Oracle database:

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

  • 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.

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

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

  • 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.

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

• 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 the UTF-8 character set is used in the source database, we recommend that you use a compatible character set, such as UTF-8 or UTF-16, in the target database 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 synchronization.

  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 task.

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

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

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

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

  If forward switchover is enabled for the data migration task, the data transmission service will automatically drop the hidden columns and unique indexes based on the type of the migration task. For more information, see Mechanisms for handling hidden columns.

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

  • We recommend that you configure the mappings between the source and target databases by specifying matching rules.

  • We recommend that you manually create schemas at the target. 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 with the ROW_MOVEMENT value set to enable.

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

• If you selected only Incremental Synchronization when you created the data migration task, the data transmission service requires that the local incremental logs of the source database be retained for at least 48 hours.

  If you selected Full Migration and Incremental Synchronization when you created the data migration task, the data transmission service requires that the local incremental logs of the source database be retained for at least 7 days. If the data transmission service cannot obtain incremental logs, the data migration task may fail or even the data between the source and target databases may be inconsistent after migration.

• If the source or target database contains table objects that differ only in letter cases, the data migration results may not be as expected due to case insensitivity in the source or target database.

Supported source and target instance types

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

Data type mappings

Create a data migration task

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

   For more information, see Purchase a data migration task.

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

   

   If you want to reference the configurations of an existing task, click Reference Configuration. For more information, see Reference the configuration of a data migration task.

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

   Parameter	Description

   Parameter	Description
   Migration Task 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.
   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 and create one in the dialog box that appears on the right. For more information about the parameters, see Create an OceanBase data source.
   Target	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 and create one in the dialog box that appears on the right. For more information about the parameters, see Create an Oracle data source.
   Tag (Optional)	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 tasks.

4. Click Next. On the Select Migration Type page, select One-way Synchronization for Synchronous Topology.

   The data transmission service supports both one-way and two-way synchronization. This topic describes how to configure one-way synchronization task. For information about two-way synchronization, see Configure a two-way synchronization task.

5. Select a type for the current data migration task.

   If you select One-way Synchronization for Synchronous Topology, the supported migration types are Schema Migration, Full Migration, Incremental Synchronization, Full Verification, and Reverse Increment.

   

   Migration type	Description

   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 target 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 target 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 target database. Options for Incremental synchronization are DML synchronization and DDL synchronization. You can select operations as needed. For more information, see Configure DDL/DML synchronization. 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, the data migration may be interrupted. 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 target 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 selected Incremental Synchronization but did not select all DML operations in the DML Synchronization section, you cannot select Full Verification.
   Reverse incremental synchronization	Data changes made in the target database after the business database switchover are synchronized to the source database in real time through reverse incremental synchronization. Generally, incremental synchronization configurations are reused for reverse incremental synchronization. You can also customize the configurations for reverse incremental synchronization as needed.

6. Click Next. On the Select Migration Objects page, specify migration objects for the data migration task.

   You can select Specify Objects or Match Rules to specify the migration objects. This topic describes how to use Specify Objects to specify the migration objects. For information about matching rules, see the "Wildcard patterns for data migration/synchronization between databases" section in the Configure and modify matching rules topic.

   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 task.

   • If you have selected DDL synchronization on the Select Migration Type page, we recommend that you select migration objects by using the Match Rules option. This way, all new objects that meet the migration rules will be synchronized. If you select migration objects by using the Specify Objects option, new or renamed objects will not be synchronized.

   

   1. In the Select Migration Objects section, select Specify Objects.

   2. In the Source Object(s) list of the Specify Migration Scope section, select the objects to migrate. You can select tables and views of one or more databases.

   3. Click > to add them to the Target Object(s) list.

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

   Note

   When you select Match Rules to specify migration objects, object renaming is implemented based on the syntax of the specified matching rules. In the operation area, you can only set filter conditions. For more information, see Configure and modify matching rules.

   Operation	Description

   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 the settings of migration objects. Click Validate. After you import the migration objects, check their validity. Column field mapping is not supported at present. After the validation succeeds, click OK.
   Rename objects	The data transmission service allows you to rename migration objects. For more information, see Rename a database table.
   Configure 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 one or all objects	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.

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

   • Full migration

     The following table describes the parameters for full migration, which are displayed only if you have selected One-way Synchronization and Full Migration in sequence on the Select Migration Type page.

     

     Parameter	Description

     Parameter	Description
     Read Concurrency	The concurrency for reading data from the source during full migration. The maximum value is 512. A high read concurrency may incur excessive stress on the source, affecting the business.
     Write Concurrency	The concurrency for writing data to the target during full migration. The maximum value is 512. A high write concurrency may incur excessive stress on the target, affecting the business.
     Full Migration Rate Limit	You can choose whether to limit the full migration rate as needed. If you choose to limit the full migration rate, you must specify the records per second (RPS) and bytes per second (BPS). The RPS specifies the maximum number of data rows migrated to the target per second during full migration, and the BPS specifies the maximum amount of data in bytes migrated to the target per second during full migration. Note The RPS and BPS values specified here are only for throttling. The actual full migration performance is subject to factors such as the settings of the source and target and the instance specifications.
     Handle Non-empty Tables in Target Database	Valid values are Ignore and Stop Migration. If you select Ignore, when the data to be inserted conflicts with existing data of a target table, the data transmission service logs the conflicting data while retaining the existing data. Important If you select Ignore, data is pulled in IN mode during full verification. In this case, verification is inapplicable if the target contains data that does not exist in the source, and the verification performance is downgraded. If you select Stop Migration and a target table contains records, an error prompting migration unsupported is reported during full migration. In this case, you must process the data in the target table before continuing with the migration. Important If you click Restore in the dialog box prompting the error, the data transmission service ignores this error and continues to migrate data. Proceed with caution.
     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 you have selected both Schema Migration and Full Migration 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 use a CLI client to modify the following parameters for business tenants based on the hardware conditions of OceanBase Database and your current business traffic:

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

   • Incremental synchronization

     The following parameters are displayed only if you have selected One-way Synchronization and Incremental Synchronization in sequence on the Select Migration Type page.

     

     Parameter	Description

     Parameter	Description
     Write Concurrency	The concurrency for writing data to the target during incremental synchronization. The maximum value is 512. A high write concurrency may incur excessive stress on the target, affecting the business.
     Incremental Synchronization Rate Limit	You can choose whether to limit the incremental synchronization rate as needed. If you choose to limit the incremental synchronization rate, you must specify the RPS and BPS. The RPS specifies the maximum number of data rows synchronized to the target per second during incremental synchronization, and the BPS specifies the maximum amount of data in bytes synchronized to the target per second during incremental synchronization. Note The RPS and BPS values specified here are only for throttling. The actual incremental synchronization performance is subject to factors such as the settings of the source and target and the instance specifications.
     Incremental Synchronization Start Timestamp	This parameter is not displayed if you have selected Full Migration on the Select Migration Type page. 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.

   • Reverse incremental synchronization

     The following parameters are displayed only if you have selected One-way Synchronization and Reverse Increment in sequence on the Select Migration Type page. By default, incremental synchronization configurations are reused for reverse incremental synchronization.

     

     You can choose not to reuse the incremental synchronization configurations and configure reverse incremental migration as needed.

     Parameter	Description

     Parameter	Description
     Write Concurrency	The concurrency for writing data to the source during reverse incremental synchronization. The maximum value is 512. A high concurrency may incur excessive stress on the source, affecting the business.
     Reverse Increment Rate Limit	You can choose whether to limit the reverse incremental synchronization rate as needed. If you choose to limit the reverse incremental synchronization, you must specify the RPS and BPS. The RPS specifies the maximum number of data rows synchronized to the source per second during reverse incremental synchronization, and the BPS specifies the maximum amount of data in bytes synchronized to the source per second during reverse incremental synchronization. Note The RPS and BPS values specified here are only for throttling. The actual reverse incremental synchronization performance is subject to factors such as the settings of the source and target and the instance specifications.
     Incremental Synchronization Start Timestamp	This parameter is not displayed if you have selected Full Migration on the Select Migration Type page. If you have selected Incremental synchronization but not Full Migration, the forward switchover start timestamp (if any) is used by default. This parameter cannot be modified.

   • Advanced parameters

     

     Parameter	Description

     Parameter	Description
     Add hidden columns for tables without non-null unique keys	This parameter is required only if you create a task to migrate data from an Oracle tenant of OceanBase Database to an Oracle database. For more information, see Hidden column mechanism of the data transmission service.
     Source table object storage type	This parameter is displayed only if the source is OceanBase Database V4.3.0 or later and you have selected DDL Synchronization for Reverse Increment on the Select Migration Type page. This parameter specifies the storage type for source table objects during reverse incremental synchronization. The storage types supported for source table objects are Default, Row storage, Column storage, and Hybrid columnar storage. For more information, see default_table_store_format. Note The value Default means that other parameters are automatically set based on the parameter configurations of the target. New table objects in reverse incremental DDL synchronization are written to corresponding schemas based on the specified storage type.

8. Click Precheck to start a precheck on the data migration task.

   During the precheck, the data transmission service checks the read and write privileges of the database users and the network connections of the databases. A data migration task can be started only after it passes all check items. If an error is returned during the precheck, you can perform the following operations:

   • Identify and troubleshoot the problem and then perform the precheck again.

   • Click Skip in the Actions column of the failed precheck item. In the dialog box that prompts the consequences of the operation, click OK.

9. After the precheck succeeds, click Start Task.

   If you do not need to start the task now, click Save. You can start the task later on the Migration Tasks page or by performing batch operations. For more information about batch operations, see Perform batch operations on data migration tasks.

   The data transmission service allows you to modify the migration objects and their row filtering conditions when a migration task is running. For more information, see View and modify migration objects and their filter conditions. After the data migration task is started, it is 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 and modify matching rules

• View details of a data migration task