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, which can be a physical data source or an ApsaraDB for OceanBase data source, to an Oracle database.

Background

You can create a data migration project in the OMS console to seamlessly 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 merge 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 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, OMS 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

• 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.

• 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.

Limitations

• Limitations on the source database

  Do not perform DDL operations that modify database or table schemas during schema migration or full data migration. Otherwise, the data migration project may be interrupted.

• At present, Oracle Database 10g, 11g, 12c, 18c, and 19c are supported. Oracle Database 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 merge only tables with primary keys.

• OMS does not support expression-based indexes.

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

• OMS does not support primary keys that contain data of the FLOAT or DOUBLE type.

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

• 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.

• In a project for migrating data from an Oracle tenant of OceanBase Database to an Oracle database of version 12c or later, OMS does not support the migration of database objects, such as schemas, tables, and columns, whose name exceeds 30 bytes in length in the reverse incremental migration step.

• OMS supports the migration of only objects whose database name, table name, and column name are ASCII-encoded and do not contain special characters. The special characters are spaces, line breaks, and the following characters: . | " ' ` ( ) = ; / & \.

• OMS does not support a standby OceanBase database as the source.

• During reverse incremental migration from an Oracle tenant of OceanBase Database to an Oracle database, OMS does not support some UPDATE statements in the source database. For example, the following UPDATE statement is not supported:

  UPDATE TABLE_NAME SET KEY=KEY+1;
  

  In the preceding example, TABLE_NAME is the table name, and KEY is a primary key column of the NUMERIC type.

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 the Store component to specify the instances for which incremental logs are to be pulled from the standby database. The procedure is as follows:

  1. Stop the Store component 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 vertical bars (|), for example, 1|2|3. For more information about how to update a store component, see Update a store component.

  3. Restart the Store component.

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

• If you need to synchronize incremental data from an Oracle database, we recommend that you restrict the size of a single archive file in the Oracle database to 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 the Store component 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 archive files or an exception in the Store component, restoration may fail due to the lack of required archive files.

• If you use OceanBase Database V4.x, we recommend that you enable log archiving. If you enable log archiving, OMS implements incremental synchronization by consuming archive logs after clogs are recycled. For more information about how to enable log archiving, see the Log archive chapter.

• If a table does not have a primary key but contains data of a 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.

  OMS cannot migrate tables without a primary key when OceanBase Database is of a version earlier than V2.2.30.

• A table containing a primary key or a non-null unique key, which must not be a function-based unique key, is considered a table with a primary key.

  If the source OceanBase database is of a version earlier than V2.2.77 or a source table contains a function-based unique key on a virtual column, OMS may fail to accurately identify whether the table contains a function-based unique key, which may lead to misjudgment of the table with a primary key. This may slow down full migration and full verification and cause data inconsistency in incremental synchronization.

• 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 of a version earlier than V3.2.x to an Oracle database, if the source table is a multi-partition table with a global unique index and you update the values of the partitioning key of the table, data may be lost during migration.

• When DDL synchronization is disabled, if you change the unique index of the destination, you must restart the Incr-Sync component. Otherwise, the data may be inconsistent.

• If forward switchover is disabled for a data migration project, drop the unique indexes and pseudocolumns from the destination. 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.

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

• Take note of the following points if you want to perform data merge migration:

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

  • We recommend that you manually create schemas at the destination. 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 "source-primary-database ROW_MOVEMENT check" precheck item during the migration, data inconsistency is expected during the synchronization of a table whose value of the ROW_MOVEMENT field is 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.

• If you select only Incremental Synchronization when you create a data migration project, OMS requires that the local incremental logs in the source database be retained for more than 48 hours.

  If you select Full Data Migration and Incremental Synchronization when you create a data migration project, OMS requires that the local incremental logs in the source database be retained for at least 7 days. Otherwise, the data migration project will fail or the data in the source and destination databases will be inconsistent because OMS cannot obtain incremental logs.

Data type mappings

Procedure

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 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 a data source for the Oracle tenant of OceanBase Database, which can be a physical data source or an ApsaraDB for OceanBase data source, select it from the drop-down list. If not, 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 a physical OceanBase data source or Create a public cloud OceanBase data source.
   Destination	If you have created an Oracle data source, select it from the drop-down list. If not, 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. 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 uses a data source in primary/standby databases mode as an example.

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

   

   Options for Migration Type are Schema Migration, Full Data Migration, Incremental Synchronization, Full Verification, and Reverse Increment.

   Migration type	Description
   Schema migration	When a schema migration task starts, OMS migrates the definitions of data objects, such as tables, indexes, constraints, comments, and views, from the source database to the destination database. Temporary tables are automatically filtered out.
   Full migration	When a full migration task starts, OMS migrates the existing data from tables in the source database to the 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. For more information, see Manually collect statistics.
   Incremental synchronization	When an incremental synchronization task starts, OMS synchronizes changed data in the source database to the corresponding tables in the destination database. Data changes are data addition, modification, and deletion. 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 Synchronize DDL operations 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 that cannot be synchronized by OMS in the source database, data migration may be interrupted. 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	After the full data migration and incremental data synchronization are completed, OMS automatically initiates a full data verification task to verify the data 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 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	When a reverse incremental migration task starts, OMS migrates the data changed in the destination database after the business switchover back to the source database in real time. You cannot select Reverse Increment in the following cases: Data merge migration that involves multiple tables is enabled. Multiple source schemas map to the same destination schema.

4. (Optional) Click Next.

   If you have selected Schema Migration or Incremental Synchronization but the related parameters are not configured for the source Oracle tenant of OceanBase Database, the More About Data Sources dialog box appears, prompting you to configure related parameters. For more information about the parameters, see Create a physical OceanBase data source or Create a public cloud OceanBase data source.

   After you configure the parameters, click Test Connection. After the test succeeds, click OK.

5. Click Next. On the Select Migration Objects page, specify the migration objects and migration scope.

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

   • 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.

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

     • OMS automatically filters out unsupported tables.

     OMS also allows you to import objects from text, rename objects, set row filters, view column information, and remove a single object or all objects to be migrated.

     

     Operation	Description
     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 objects	OMS allows you to rename the migration objects. For more information, see Rename a migration or synchronization object.
     Configure 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 one or all objects	During data mapping, OMS allows you to remove one or more selected objects to be migrated or synchronized to the destination. To remove a single migration object: In the list on the right of the Specify Migration Scope section, move 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, configure the following parameters.

   • Full migration

     The following parameters are displayed only if you have selected Full Data Migration on the Select Migration Type page.

     

     Parameter	Description
     Full Migration Resource Configuration	You can select Small, Medium, or Large to use the corresponding default values of Read Concurrency, Write Concurrency, and Memory. You can also customize the resource configurations for full migration. Through resource configuration for the Full-Import component, you can limit the resource consumption of a project in the full migration phase. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.
     Processing Strategy When Destination Table Has Records	Valid values: Ignore and Stop Migration. If you select Ignore, when the data to be written conflicts with the existing data of a destination table, OMS logs the conflicting data while retaining the existing data. Notice If you select Ignore, data is pulled in IN mode for full verification. In this case, the scenario where the destination contains more data than the source cannot be verified, and the verification efficiency will be decreased. If you select Stop Migration and a destination table contains records, an error is returned during full migration, indicating that the migration is not allowed. In this case, you must clear the data in the destination table before you can continue with the migration. Notice After an error is returned, if you click Resume in the dialog box, OMS 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. Notice This feature is supported only if you have selected both Schema Migration and Full Data Migration on the Select Migration Type page. Only non-unique key indexes can be created after the migration is completed. OceanBase Database V1.x does not support the post-indexing feature.

     If post-indexing is allowed, we recommend that you adjust the parameters based on the hardware conditions of your OceanBase database and the current business traffic.

     • If you use OceanBase Database V4.x, adjust the following parameters of the sys tenant and business tenants by using a CLI client.

       • Adjust the parameters of the sys tenant

         // parallel_servers_target specifies the queuing conditions 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 parameters 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 V2.x or V3.x, adjust the following parameters of the sys tenant by using a CLI client.

       // parallel_servers_target specifies the queuing conditions 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; 
       

   • Incremental synchronization

     The following parameters are displayed only if you have selected Incremental Synchronization on the Select Migration Type page.

     

     Parameter	Description
     Incremental Log Pull Resource Configuration	You can select Small, Medium, or Large to use the corresponding default value of Memory. You can also customize the resource configurations for incremental log pull. Through resource configuration for the Store component, you can limit the resource consumption of a project in log pull in the incremental synchronization phase. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.
     Incremental Data Write Resource Configuration	You can select Small, Medium, or Large to use the corresponding default values of Write Concurrency and Memory. You can also customize the resource configurations for incremental data write. Through resource configuration for the Incr-Sync component, you can limit the resource consumption of a project in data writes in the incremental synchronization phase. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.
     Incremental Record Retention Time	The duration that incremental parsed files are cached in OMS. A longer retention period results in more disk space occupied by the Store component.
     Incremental Synchronization Start Timestamp	If you have set the migration type to Full Data Migration, this parameter is not displayed. If you have selected Incremental Synchronization but not Full Data 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 migration

     The following parameters are displayed only if you have selected Reverse Increment on the Select Migration Type page. The parameters for reverse incremental migration are consistent with those for incremental synchronization. You can select Reuse Incremental Synchronization Configuration in the upper-right corner.

     

   • Full verification

     The following parameters are displayed only if you have selected Full Verification on the Select Migration Type page.

     

     Parameter

     Description

     Full Verification Resource Configuration

     You can select Small, Medium, or Large to use the corresponding default values of Read Concurrency and Memory. You can also customize the resource configurations for full verification. Through resource configuration for the Full-Verification component, you can limit the resource consumption of a project in the full verification phase. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.

   If the parameter settings on the page cannot meet your requirements, you can click Parameter Configuration in the lower part of the page to configure more specific settings. You can also reference an existing project or component template.

   

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. You can perform one of the following operations if an error is returned during the precheck:

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

   • Click Skip in the Actions column of a failed precheck item. In the dialog box that appears, you can view the prompt for the consequences of the operation and click OK.

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 subtasks will be executed based on the selected migration types. For more information, see the "View migration details" section in the View details of a data migration project topic.