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: primary database only, standby database only, 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.

• 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.

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

• 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.

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

• OMS can parse up to 5 TB of incremental logs of Oracle databases per day.

• When Oracle Database is of a version earlier than 11g, the database object name cannot exceed 30 bytes in length. 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.

• 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.

Considerations

• When the Oracle database is in standby database only or primary/standby databases mode, if the number of instances that run on the primary Oracle database differs from that on the standby database, incremental logs of some instances may not be pulled. You need to manually set the parameters of Oracle Store to specify the instances for which incremental logs are to be pulled from the standby database. The procedure is as follows:

  1. Stop Oracle Store as soon as it starts.

  2. On the Update Configuration page of the Store component, add the deliver2store.logminer.instance_threads parameter and specify the instances for which logs are to be pulled.

     Separate multiple threads with a vertical bar (|), for example, 1|2|3. For more information about how to update a store component, see Update a store component.

  3. After you set the parameters, restart Oracle Store.

  4. Wait for five minutes, and then run the grep 'log entries from' connector/connector.log command to check the instance logs pulled. The thread field indicates the instances for which the logs are pulled.

• If you need to migrate incremental data from an Oracle database, we recommend that you restrict the size of a single archive file in the Oracle database within 2 GB. An excessively large archive file may incur the following risks:

  • The log pulling time increases not in proportion to the size of a single archive file, but much more sharply.

  • When the Oracle database is in standby database only or primary/standby databases mode, the incremental data is pulled from the standby database. In this case, only archive files can be pulled. An archive file is pulled after it is generated. A larger archive file means a longer delay before the archive file is processed, and a longer time for processing the archive file.

  • In addition, a larger size of a single archive file means larger memory required by Oracle Store under the same data pulling concurrency.

• The 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 archived files or an exception in Oracle Store, restoration may fail due to the lack of required archive files.

• 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.

• 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.

• 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.

• 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 for migrating data 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 destination 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. When a data migration project is in the forward switchover step, OMS will automatically drop the hidden columns and unique indexes based on the type of the data migration project. For more information, see Schema migration mechanisms.

• 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.

• If you use Oracle Database 12c or later and have configured Reverse Incremental Migration, perform the following operations to migrate incremental database objects whose names are more than 30 bytes in length.

  1. Execute the following statement as the SYS user to modify parameters of the Oracle database: ALTER SYSTEM SET ENABLE_GOLDENGATE_REPLICATION=true SCOPE=BOTH;.

     Notice:

     For Oracle Real Application Clusters (RAC), you need to modify the parameters for all Oracle instances. You do not need to restart the Oracle database.

  2. Execute the ALTER SYSTEM SWITCH LOGFILE; statement three times for each Oracle instance.

  3. After 10 minutes, re-create a data migration project.

  4. Set deliver2store.logminer.need_check_object_length to false for Oracle Store.

• 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.

• 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 "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. 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 an Oracle data source, select it from the drop-down list. If you have not created an Oracle 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 about the parameters, see Create an Oracle data source. You can select an Oracle data source in primary database only mode or primary/standby databases mode. An Oracle data source in standby database only 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 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. If the source and destination databases use different character sets, OMS does not support modifications of schema fields. 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 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 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 the DML Synchronization section, OMS does not support full verification.
   Reverse incremental migration	For Oracle 12c or later, when you add or change a column, 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 in the Oracle database, and set deliver2store.logminer.need_check_object_length=false for Oracle Store. 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 is 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 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.

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 have selected 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 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 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. 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.

6. 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.

7. 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.

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 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.