Migrate data from an Oracle tenant of OceanBase Database to a DB2 LUW database

This topic describes how to use OceanBase Migration Service (OMS) to migrate data from an Oracle tenant of OceanBase Database to a DB2 LUW database.

Prerequisites

• You have created dedicated database users in the source Oracle tenant of OceanBase Database and the destination DB2 LUW database for data migration and granted the corresponding privileges to the users. For more information, see Create a database user.

• DB2 LUW 10.1, 10.5, 11.1, and 11.5 for Linux and AIX are supported.

• Retain logs of OceanBase Database for at least one day in case of unexpected pullback.

Limits

• OMS cannot migrate a table without a primary key from an Oracle tenant of OceanBase Database to a DB2 LUW database.

• In an ARM architecture, OMS does not support reverse incremental migration from an Oracle tenant of OceanBase Database to a DB2 LUW database.

• OMS does not support triggers in the destination database for long-term synchronization between these databases.

• The data source identifiers and user accounts must be globally unique in OMS.

• OMS allows you to migrate only databases and tables whose names are ASCII codes and do not contain special characters such as .|"'`()=;/&\n.

• OMS supports full synchronization of tables whose partition fields are not within the primary keys, but does not support DDL operations that create tables.

• You cannot create primary keys and other indexes on an Oracle tenant of the source OceanBase database during data migration on OMS.

• Length limits

  • The data of the CHAR or BINARY type cannot exceed 255 bytes in length in a DB2 LUW database. If the data written to the Oracle tenant of OceanBase Database exceeds 255 bytes in length, an error will occur during migration.

  • The data of the VARCHAR or BINARY type cannot exceed 32 KB in length in a DB2 LUW database. If the data written to the Oracle tenant of OceanBase Database exceeds 32 KB in length, an error is returned for the data migration project.

  • The Decimal(dp, ds) in a DB2 LUW database is equivalent to the NUMBER of an Oracle tenant of OceanBase Database. The length of dp cannot exceed 31 and must be greater than or equal to that of ds.

    The number written to an Oracle tenant of OceanBase Database cannot exceed the maximum allowed number. By default, the data of the NUMBER, INT, SMALLINT, and NUMBER(*, s) types is 38 bytes in length in an Oracle tenant of OceanBase Database. You need to explicitly define the NUMBER(p,s) to the length that is compatible with the business application and the source and destination databases.

  • The length of data of the NCHAR type cannot exceed 63 bytes in a DB2 LUW database or 2,000 bytes in an Oracle tenant of OceanBase Database. Therefore, if a field where data of the NCHAR type exceeds 63 bytes in an Oracle tenant of OceanBase Database, the field is truncated when it is migrated to a DB2 LUW database. This causes data loss.

• Data type limits

  • The data of the TIME type in a DB2 LUW database cannot be migrated as the partitioning key.

  • The data of the XML type is not supported.

  • We do not recommend that you use CODEUNITS16 or CODEUNITS32 to define or store multi-byte data of the NCHAR, GRAPHIC, or other types.

  • The default value of the BLOB-type data cannot be modified.

  • When you migrate data from OceanBase Database V1.4.x, OMS does not support primary keys that contain data of the FLOAT or DOUBLE type.

  • Spaces on the right side of data of the VARCHAR and VARGRAPHIC types are not compared in a DB2 LUW database. If the primary key lacks a space during incremental data synchronization, the data can become inconsistent. This causes data loss in the destination database.

  • Note that when a data type in a DB2 LUW database is converted to the LOB type in an Oracle tenant of OceanBase Database, the data of the LOB type cannot exceed 48 MB in size.

Considerations

• If the character set used by the source database is UTF-8, we recommend that you use UTF-8 or a greater character set for the destination database.

• A table containing a primary key or a not-null unique key but not a function-based unique key is a table with a primary key. If a table in the source Oracle tenant of OceanBase Database contains a function-based unique key in a virtual column, or if the database version is earlier than V2.2.77, OMS cannot accurately identify whether the table contains a function-based unique key and therefore may be inaccurate in determining whether the table has a primary key. This may slow down full migration and full verification and result in data inconsistency in incremental synchronization.

  During incremental synchronization, data is parallelized based on the unique constraint of data. However, during the incremental synchronization of a table containing a function-based unique key, related transaction operations must be serialized to avoid data inconsistency. Information about whether a table containing a function-based unique key exists must be provided by the management and control layer. If you enable DDL synchronization, the drop index command is executed on all indexes, which may cause index loss in the destination database.

• In a project for migrating data from an Oracle tenant of OceanBase Database to a DB2 LUW database, when the Oracle tenant is of a version earlier than V3.2.x and has a multi-partition table with global unique indexes, if you update the value of a partitioning key of the table, data may be lost during migration.

• If the clocks are out of synchronization between the nodes or between the client and the server, a negative delay may occur in incremental synchronization or reverse incremental synchronization.

• If you change the unique index of the destination, you must restart the incremental synchronization. Otherwise, the data may be inconsistent.

• If you select migration objects based on matching rules, we recommend that you create standard CTAS statements and set object exclusion rules, such as a.ctas*, to avoid interrupting the data migration project.

• In a multi-table aggregation scenario:

  • We recommend that you map objects in the source and destination databases by importing objects and configuring matching rules.

  • We recommend that you manually create schemas in the destination database. If you use OMS to create schemas, skip failed objects in the schema migration step.

• If you skip the "Check the ROW_MOVEMENT parameter of the database" check item of the source primary database during the migration, data inconsistency may occur when you synchronize tables whose ROW_MOVEMENT is enable.

Data type mapping

Create a data migration project

1. Create a data migration project.

   1. Log on to the OMS console.

   2. In the left-side navigation pane, click Data Migration.

   3. On the Data Migration page, click Create Migration Project in the upper-right corner.

2. On the Select Source and Destination page, specify the following 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	Click the field and select a target tag from the drop-down list. You can 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 a data source for the Oracle tenant of OceanBase Database, select it from the drop-down list. Only tables with primary keys or unique keys are displayed. If you have not created a data source for the Oracle tenant, click Create Data Source in the drop-down list and create one in the dialog box that appears on the right. For more information, see Create a physical data source of OceanBase Database. Notice The source cannot be an Oracle tenant of OceanBase Database V4.0.0.
   Destination	If you have created DB2 LUW data sources, select one from the drop-down list. If you have not created a DB2 LUW data source, click Create Data Source in the drop-down list and create one in the dialog box that appears on the right. For more information, see Create a DB2 LUW data source. Notice The column specified as the unique key in a DB2 LUW database must have the NOT NULL constraint.

3. Click Next.

4. In the dialog box that appears, click OK.

   Note that this project supports only tables with a primary key or a non-null unique index and other tables are automatically filtered out.

5. On the Select Migration Type page, specify related parameters.

   Options available for Migration Type include Schema Migration, Full Migration, Incremental Synchronization, Full Verification, and Reverse Incremental Migration.

   Migration type	Description
   Schema Migration	The definitions of data objects, such as tables, indexes, constraints, comments, and views, are migrated from the source database to the destination database. Temporary tables are automatically filtered out.
   Full Migration	If you select Full Migration, we recommend that you collect the statistics of the Oracle tenant of OceanBase Database before the data migration. For more information, see Manually collect statistics.
   Incremental Synchronization	Options for Incremental Synchronization are DML Synchronization and DDL Synchronization. You can select the options as needed. For more information about DDL synchronization, see DDL synchronization between an Oracle tenant of OceanBase Database and a DB2 LUW database. Incremental Synchronization has the following limits: < If you select DDL Synchronization, when you perform a DDL operation that is not supported by OMS in the source database, data migration may fail. If the DDL operation creates a new column, we recommend that you set the attribute of the column to Null. Otherwise, data migration may be interrupted.
   Full Verification	If you select Full Verification, we recommend that you collect the statistics of the Oracle tenant of OceanBase Database and use the RUNSTATS statement to collect the statistics of the DB2 LUW database before the full verification. If you have selected Incremental Synchronization but did not select all DML statements in the DML Synchronization section, OMS does not support full verification.
   Reverse Incremental Migration	You cannot select Reverse Incremental Migration in the following cases: Multi-table aggregation and synchronization is enabled. Multiple schemas are configured in a rule to match one type of objects.

6. (Optional) Click Next.

   When the source database is an Oracle tenant of OceanBase Database:

   • If incremental synchronization needs to be performed, specify the ConfigUrl, username, and password.

   • If only schema migration needs to be performed, specify the username and password.

   If you have selected Schema Migration or Incremental Synchronization but no corresponding parameters are configured for the data source of the source Oracle tenant of OceanBase Database, the More about Data Sources dialog box appears, prompting you to configure related parameters. For more information, see Create a physical data source of OceanBase Database.

   After you configure the parameters, click Test Connectivity. After the test succeeds, click Save.

7. Click Next. On the Select Migration Objects page, select the migration objects and migration scope.

   You can select one of the following two modes to migrate objects: Specify Objects or Match Rules. If you have selected DDL Synchronization, only the Match Rules option is available.

   • Select Specify Objects. Then 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.

     Notice

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

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

     When you migrate data from an Oracle tenant of OceanBase Database to a DB2 LUW database, OMS allows you to import objects by using text files, rename object names, set row filters, view column information, and remove one or all objects to be migrated.

     Operation	Steps
     Import Objects	In the list on the right of the Specify Migration Scope section, click Import Objects in the upper-right corner. In the dialog box that appears, click OK. Notice 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/tables and set row filtering conditions. For more information, see Download and import the settings of migration objects. Click Validate. After the validation succeeds, click OK.
     Rename	OMS allows you to rename the migration objects. For more information, see Rename a database table.
     Settings	OMS allows you to use the WHERE clause to filter rows. For more information, see Use SQL conditions to filter data You can also view column information of the migration object in the View Column section.
     Remove/Remove All	During data mapping, OMS allows you to remove one or more selected objects to be migrated to the destination. To remove a single migration object: In the list on the right of the Specify Migration Scope section, hover the pointer over the target object, and click Remove. To remove all migration objects: In the list on the right of the Specify Migration Scope section, click Remove All in the upper-right corner. In the dialog box that appears, click OK.

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

8. Click Next. On the Migration Options page, specify the following parameters.

   Parameter	Description
   Incremental Synchronization Start Timestamp	If you have set the migration type to Full Migration, this parameter is not displayed. If you have selected a migration type other than Full Migration, specify a point in time after which the data is to be synchronized. The default value is the current system time. You can select a point in time or enter a timestamp. Notice You can select the current time or a point in time earlier than the current time. This parameter is closely related to the retention period of archived logs. Generally, you can start data synchronization from the current timestamp.
   Concurrency for Full Migration	The value can be Smooth, Normal, or Fast. The quantity of resources to be consumed by a full data migration task varies based on the migration performance. You can also modify the configurations of the Full-Import component to customize the concurrency. Notice: To enable this feature, select Full Migration on the Select Migration Type page.
   Full Verification Concurrency	The value can be Smooth, Normal, or Fast. Different quantities of resources of the source and destination databases are consumed at different concurrencies. You can also modify the configurations of the Full-Verification component to customize the concurrency.
   Incremental Record Retention Time	The duration that incremental parsed files are cached in OMS. A longer retention period indicates more disk space occupied by the Store component of OMS.
   Whether to Allow Destination Table to Be Not Empty During Full Migration	If destination tables are allowed to be not empty during full migration, full verification is performed in IN mode. Notice: To enable this feature, select Full Migration on the Select Migration Type page.
   Whether to Allow Post-indexing	You can specify whether to allow post-indexing after full migration is completed. Post-indexing can shorten the time of full migration. Notice: To enable this feature, select 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.

9. Click Precheck to start a pre-check on the data migration project.

   During the pre-check, OMS 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. If an error is returned during the pre-check:

   • You can identify and troubleshoot the problem and then perform the pre-check again.

   • You can click Skip in the Actions column of the pre-check item with the error. A dialog box will be displayed, prompting the impact caused if you skip this error. If you want to continue, click OK in the dialog box.

10. Click Start Project. If you do not need to start the project now, click Save to go to the details page of the data migration project. You can start the project later as needed.

OMS allows you to modify the migration objects when the data migration project is running. For more information, see View and modify migration objects. After a data migration project is started, the migration objects will be executed based on the selected migration type. For more information, see the "View migration details" section in the View details of a data migration project topic.