Create a project to migrate data from an Oracle tenant of OceanBase Database to an Oracle database

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

Background

You can create a data migration project in the OMS console to migrate the existing business data and incremental data from an Oracle tenant of OceanBase Database to an Oracle database through schema migration, full migration, and incremental synchronization.

The Oracle database supports the following modes: single primary database, single standby database, and primary/standby databases. The following table describes the data migration operations supported by each migration mode.

OMS allows you to aggregate the data of multiple tables of an Oracle tenant of OceanBase Database to the same table in an Oracle database without schema migration. You only need to perform full migration and incremental synchronization. The aggregation and synchronization feature has the following limits:

• For full migration and incremental synchronization, the destination table must contain all columns that exist in the source table. Otherwise, OMS 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

• You have created a corresponding schema in the destination database. OMS allows you to migrate tables and columns. Therefore, you must create a corresponding schema in the destination database before migration.

• 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.

• If you want to migrate tables without primary keys, create the __oceanbase_inner_drc_user user in the corresponding tenant and grant privileges to the user before you perform the data migration project. For more information, see Create the __oceanbase_inner_drc_user user.

Limits

• OMS supports the following Oracle Database versions: 10g, 11g, 12c, 18c, and 19c. Version 12c and later provide container databases (CDBs) and pluggable databases (PDBs).

• Incremental data migration is not supported for a table whose data in all columns is of the following three large object (LOB) types: BLOB, CLOB, and NCLOB.

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

• You cannot migrate data from a non-template-based subpartitioned table in an Oracle tenant of OceanBase Database to an Oracle database.

• You can aggregate only tables with primary keys.

• OMS does not support expression-based indexes.

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

• 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.

• 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.

• OMS supports character sets of Oracle databases and Oracle tenants of OceanBase Database. The field length varies with 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 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.

• 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 the source table contains the OMS_PK_INCRMT field, the JDBC connector exits when a DML operation is performed during incremental synchronization of the table. The incremental synchronization process is interrupted and cannot be recovered.

• In a project of migration from an Oracle tenant of OceanBase Database to an Oracle 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 you change the unique index of the destination, you must restart the incremental synchronization. Otherwise, the data may be inconsistent.

• If forward switchover is not started in a data migration project, delete the unique indexes and pseudocolumns from the source database. If you do not delete 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.

Data type mappings

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, configure the parameters.

   Parameter	Description
   Migration Project Name	We recommend that you set it to a combination of Chinese characters, digits, and letters. It must not contain any spaces and cannot exceed 64 characters in length.
   Label	Click the field and select the 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 Oracle tenants in OceanBase Database as data sources, select one from the drop-down list. If you have not created a data source, click Create Data Source in the drop-down list and create a data source in the dialog box that appears on the right. For more information, see Create OceanBase Database physical tables as a data source.
   Destination	If you have created an Oracle data source, select it from the drop-down list. If you have not created a data source, click Create Data Source in the drop-down list and create a data source in the dialog box that appears on the right. For more information, see Create an Oracle data source. You can select an Oracle data source in single primary database mode or primary/standby databases mode. An Oracle data source in single standby database mode cannot serve as the destination for data migration. This topic describes how to create a data migration project with an Oracle data source in primary/standby databases mode.

3. Click Next. On the Select Migration Type page, specify the following parameters.

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

   Migration type	Limits
   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.
   Incremental Synchronization	Options for Incremental Synchronization are DML Synchronization and DDL Synchronization. The DML operations for synchronization are Insert, Delete, and Update. You can select the operations as needed. If the source and destination databases use different character sets, OMS does not support modifications of schema fields. For more information, see Supported DDL operations for incremental migration from an Oracle tenant of OceanBase Database to an Oracle database. Incremental Synchronization has the following limits: If you do not select DDL Synchronization, ensure that the source database involves no modifications and that the incremental DML data has been synchronized to the destination before DDL modifications. Then, perform related DDL operations in the source and destination databases respectively. If you do not select DDL Synchronization, for DDL operations on tables in the migration link, perform these operations in the destination database first. Otherwise, data migration may fail. If you have selected DDL Synchronization, when you perform a DDL operation for incremental migration that is not supported by OMS in the source database, data migration may fail.
   Full Verification	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 the full verification. If you have selected Incremental Synchronization but did not select all DML statements in DML Synchronization, OMS does not support full data verification in this scenario.
   Reverse Incremental Migration	For Oracle 12c or later versions, if you select Reverse Incremental Migration, when you add or change a column in the destination database, the table name and column name cannot exceed 30 bytes in length. If you want the database to support table names and column names of more than 30 bytes in length, specify the ENABLE_GOLDENGATE_REPLICATION parameter as the SYS user, and set deliver2store.logminer.need_check_object_length to false. Set ENABLE_GOLDENGATE_REPLICATION as follows: For a Real Application Cluster (RAC) environment, set this parameter for each node. If the Oracle database is in Active Data Guard (ADG) mode, set this parameter in the ADG source database. alter system set ENABLE_GOLDENGATE_REPLICATION=true SCOPE=BOTH; Query ENABLE_GOLDENGATE_REPLICATION as follows. SELECT K.KSPPINM,V.KSPPSTVL FROM SYS.X$KSPPI K,SYS.X$KSPPSV V WHERE K.INDX=V.INDX AND UPPER(K.KSPPINM) = 'ENABLE_GOLDENGATE_REPLICATION'; You cannot select Reverse Incremental Migration in the following cases: Multi-table aggregation and synchronization are enabled. Multiple schemas are configured in a rule to match one type of objects.

4. (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 select 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 OceanBase Database physical tables as a data source.

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

5. 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 select Synchronization DDL, 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 name of a table to be migrated and the names of columns in the table 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 an Oracle database, OMS allows you to import objects through text, 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. NoticeThis 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	In the list on the right of the Specify Migration Scope section, hover the pointer over the target object. Click Rename. Enter a new name and click OK.
     Settings	OMS allows you to set WHERE conditions to filter data by row and view column information. In the list on the right of the Specify Migration Scope section, hover the pointer over the target object. Click Settings. In the Settings dialog box, specify a standard SQL WHERE clause to filter data by row. The setting takes effect for full migration and incremental synchronization. Notice Add an escape character (`) for column names. Example: `col`. Only the data meeting the WHERE condition is synchronized to the destination data source, thereby filtering data by row. If row-based filtering with the WHERE clause is enabled, right-trim is forcibly performed on data of the CHAR or VARCHAR type, which may cause an inaccurate comparison of the VARCHAR data. Proceed with caution. Click OK. You can also view column information of the migration object in the View Columns section.
     Remove/Remove All	OMS allows you to remove one or more objects from the destination database during data mapping. 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. The migration object is removed. 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 to remove all migration objects.

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

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

   Parameter	Description
   Concurrency for Full Migration	The value can be Smooth, Normal, or Fast. The amount 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 checker 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 checker 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.

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

   During the precheck****, 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:

   • You can troubleshoot the error and run the precheck again.

   • You can also click Skip in the Actions column of the precheck item that returns the error. Then, a dialog box appears, indicating the impact that may be caused if you choose to skip this check item. If you want to continue, click OK in the dialog box.

8. 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 migration objects when a 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.