Migrate data from a TiDB database to OceanBase Database Community Edition

This topic describes how to use OceanBase Migration Service (OMS) Community Edition to migrate data from a TiDB database to OceanBase Database Community Edition.

Background information

OMS Community Edition allows you to create a project to seamlessly migrate the existing business data and incremental data from a TiDB database to OceanBase Database Community Edition through schema migration, full migration, and incremental synchronization.

TiDB is an integrated distributed database that supports hybrid transactional and analytical processing (HTAP). You must deploy a TiCDC cluster and a Kafka cluster to synchronize incremental data from a TiDB database to OceanBase Database Community Edition.

TiCDC is an incremental data synchronization tool for TiDB and provides high availability by using a placement driver (PD) cluster, which is the scheduling module of the TiDB cluster and usually consists of three PD nodes. TiKV Server is a TiKV node in the TiDB cluster. It sends data changes in change logs to the TiCDC cluster. TiCDC runs multiple TiCDC processes to obtain and process data from TiKV nodes, and then synchronizes the data to the Kafka cluster. The Kafka cluster saves the incremental logs of the TiDB database that are converted by TiCDC. During incremental data synchronization, OMS Community Edition obtains the corresponding data from the Kafka cluster and migrates the data to OceanBase Database Community Edition in real time. If you create a TiDB data source without binding it to a Kafka data source, you cannot perform incremental synchronization.

Prerequisites

You have created dedicated database users for data migration in the source TiDB database and OceanBase Community Edition that serves as the destination, and granted corresponding privileges to the users. For more information, see Create a database user.

Limitations

• Limitations on the source database

  Do not perform DDL operations for database or schema changes during schema migration or full data migration. Otherwise, the data migration project may be interrupted.

• Only TiDB 4.x and 5.4 are supported.

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

• OMS Community Edition does not support the migration of tables without primary keys and data with spaces from a TiDB database to OceanBase Community Edition.

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

• OMS Community Edition supports the migration of only objects whose database name, table name, and column name are ASCII-encoded without special characters. The special characters are line breaks and . | " ' ` ( ) = ; / &

• OMS Community Edition supports only the TiCDC Open Protocol. If you use an unsupported protocol, a JDBC connector exception will occur, and an error that indicates a null pointer will be returned.

Considerations

• 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.

• In the reverse incremental data migration from a TiDB database to OceanBase Database Community Edition, if OceanBase Database Community Edition is of a version earlier than V3.2.x and contains a multi-partition table that has a globally unique index, data may be lost during migration if you update the value of the partitioning key of the table.

• Do not write data to the topic synchronously used by TiCDC. Otherwise, a JDBC connector exception may occur and a null pointer error may be returned.

• Check whether the migration precision of OMS Community Edition for columns of data types such as DECIMAL, FLOAT, and DOUBLE is as expected. If the precision of the destination field type is lower than the precision of the source field type, the value with a higher precision may be truncated. This may result in data inconsistency between the source and destination fields.

• If you change the unique index of the destination, you must restart the Incr-Sync component. Otherwise, the data may be inconsistent.

• 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.

• If you configure matching rules to select tables created by using the CREATE TABLE AS SELECT (CTAS) statement as migration objects, we recommend that you configure the rules, such as a.*_2023_backup, in advance to avoid interruption of the migration project.

• In a multi-table aggregation scenario:

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

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

Data type mappings

Procedure

1. Create a data migration project.

   1. Log on to the console of OMS Community Edition.

   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	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 TiDB 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, see Create a TiDB data source. Notice If the TiDB data source is not bound to a valid Kafka data source or a topic, incremental synchronization is not supported.
   Destination	If you have created a data source of OceanBase Database Community Edition, 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 parameters, see Create a data source of OceanBase Database Community Edition.

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, configure the parameters.

   Options for Migration Type are 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	The existing data is migrated from tables in the source database to the corresponding tables in the destination database. If you select Full Migration, we recommend that you use the ANALYZE statement to collect the statistics of the TiDB database before data migration.
   Incremental synchronization	Changed data in the source database is synchronized to the corresponding tables in the destination database after an incremental synchronization task starts. Data changes are data addition, modification, and deletion. Options for DML Synchronization in the Incremental Synchronization section include Insert, Delete, and Update. For more information, see DML filtering. If you create a TiDB data source without binding it to a Kafka data source, you cannot select Incremental Synchronization.
   Full verification	After the full data migration and incremental data synchronization are completed, OMS Community Edition 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 both the source and destination databases before full verification. For more information about how to collect statistics of OceanBase Database Community Edition, see Manually collect statistics. If you select Incremental Synchronization but do not select all DML operations in the DML Synchronization section, you cannot select Full Verification.
   Reverse incremental migration	Data changes made in the destination database after the business database switchover are applied to the source database in real time. You cannot select Reverse Incremental Migration in the following cases: Multi-table aggregation and synchronization is enabled. Multiple source schemas map to the same destination schema.

6. (Optional) Click Next. If you have selected Reverse Incremental Migration but the ConfigUrl, username, or password is not configured for OceanBase Database Community Edition that serves as the destination, the More about Data Sources dialog box appears, prompting you to configure related parameters. For more information about parameters, see Create a data source of OceanBase Database Community Edition.

   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 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.

     OMS Community Edition allows you to import objects from text, rename objects, and remove a single migration object or all migration objects.

     Operation	Step
     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 Community Edition allows you to rename migration objects. For more information, see Rename a database table.
     Remove/Remove All	OMS Community Edition allows you to remove a single object or all objects to be migrated to the destination database during data mapping. 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.

   To view or modify parameters of the Full-Import or Incr-Sync component, click Configuration Details in the upper-right corner of the Full Migration or Incremental Synchronization section. For more information about the parameters, see Coordinator.

   • Full migration

     The following table describes the full migration parameters, which are displayed only when you have selected Full Migration on the Select Migration Type page.

     Parameter	Description
     Concurrency Speed	Valid values: Stable, Normal, Fast, and Custom. The amount of resources to be consumed by a full data migration task varies based on the migration performance. If you select Custom, you can set Read Concurrency, Write Concurrency, and JVM Memory as needed.
     Processing Strategy When Records Exist in Target Object	Valid values: Ignore and Stop Migration. If you select Ignore, the data in the source and destination databases may be inconsistent. If you select Stop Migration, the project is set to the Failed state when the system detects records in the destination table. To continue data migration, manually resume the project.
     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 when you have selected both Schema Migration and Full Migration on the Select Migration Type page.

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

     • If you use OceanBase Database Community Edition V4.x, adjust the following parameters of the sys tenant and business tenants by using a command-line interface (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 Community Edition 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 table describes the incremental synchronization parameters, which are displayed only when you have selected Incremental Synchronization on the Select Migration Type page.

     Parameter	Description
     Concurrency Speed	Valid values: Stable, Normal, Fast, and Custom. The amount of resources to be consumed by an incremental synchronization task varies based on the synchronization performance. If you select Custom, you can set Read Concurrency, Write Concurrency, and JVM Memory as needed.
     Incremental Synchronization Start Timestamp	If you have set the migration type to Full Migration, this parameter is not displayed. 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.
     Incremental Record Retention Time	The duration that incremental parsed files are cached in OMS Community Edition. A longer retention period results in more disk space occupied by the Store component of OMS Community Edition.

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

   During the precheck, OMS Community Edition checks the read and write privileges of the database users and the network connectivity of the databases. The data migration project can be started only after it passes all check items. If an error is returned during the precheck:

   • You can identify and troubleshoot the problem and then perform the precheck again.

   • You can also click Skip in the Actions column of the failed precheck item. A dialog box appears, prompting you the impact. If you want to skip this operation, click OK.

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 Community Edition allows you to modify the migration objects when the 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.