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). If you use TiDB 4.x or later, 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 Database 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 migration. Otherwise, the data migration project may be interrupted.

• TiDB 2.x, 3.x, 4.x, 5.x, 6.x, and 7.x are supported.

  Notice

  TiDB 2.x and 3.x support only TiDB Binlog.

• 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 Database 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

• To ensure the performance of a data migration project, we recommend that you migrate no more than 1,000 tables at a time.

• If the source contains foreign keys with the same name, an error occurs during schema migration. In this case, you can rename the foreign keys to resume the project.

• 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 reverse incremental migration from a TiDB database to OceanBase Database Community Edition of a version earlier than V3.2.x, if a source table is a multi-partition table with a global unique index and the values of the partitioning key of the table are updated, data can be lost during the migration.

• 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.

• Take note of the following considerations if you want to aggregate multiple tables:

  • We recommend that you configure the mappings between the source and destination databases by importing objects or specifying 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.

• A difference between the source and destination table schemas may result in data consistency. Some known scenarios are described as follows:

  • When you manually create a table schema, if the data type of a column in the source is not supported by OMS Community Edition, implicit data type conversion may occur, which causes inconsistent column types between the source and destination.

  • If the length of a column at the destination is shorter than that at the source, the data of this column may be automatically truncated, which causes data inconsistency between the source and destination.

• If you use TiDB 2.x or 3.x, take note of the following considerations. For more information about TiDB Binlog, see Overview.

  • TiDB Binlog does not send heartbeat packets. If the source is not updated, the timestamp of incremental synchronization is not updated.

  • Before incremental synchronization starts, the source must be updated. Otherwise, the data not existed error is reported.

  • For a table without a primary key, the information of a unique key cannot be obtained from incremental binlogs. In this case, the program uses all fields as the primary key. When an update operation in the source is synchronized to the destination, the corresponding data record is first deleted and then inserted.

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.

   For tables without a primary key and tables with a non-null unique key in the TiDB database, full migration and full verification are supported but incremental synchronization is not supported.

5. On the Select Migration Type page, configure the parameters.

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

   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	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 an object	OMS Community Edition allows you to rename migration objects. For more information, see Rename a database table.
     Remove one or all objects	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, 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.

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 if 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, when the data to be inserted conflicts with the existing data of a destination table, OMS Community Edition retains the existing data and records the conflict data. Notice If you select Ignore, data is pulled in IN mode for verification. In this case, the scenario where the destination table contains more data than the source table 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 Community Edition ignores this error and continues to migrate data. Proceed with caution.
     Writing Method	Valid values: SQL (specifies to write data to tables by using INSERT or REPLACE) and Direct Load (specifies to write data through bypass import). The limitations on the Direct Load are as follows: This write mode is supported for full migration only when the destination is an instance of OceanBase Database Community Edition of a version later than V4.2.1. The size of data in a single row cannot exceed 2 MB. Only data duplication caused by primary key constraints can be handled, and that caused by unique key constraints cannot be handled. Generated columns, triggers, and user-defined types (UDTs) are not supported. Bypass import applies to empty tables and cannot be interrupted. In other words, resumable transmission is not supported. Therefore, if bypass import is used for full migration and is interrupted, the data in the source is read again even after the project resumes normal. If an imported table contains large object (LOB) fields, execute the following statement to disable the enable_rebalance parameter for OceanBase Database Community Edition: SHOW PARAMETERS LIKE 'enable_rebalance'; ALTER SYSTEM SET enable_rebalance = false; Requests in a queue may time out if data is concurrently written in bypass mode. We recommend that you set soure.sliceWorkerNum to 1. The number and order of fields in the source table must be the same as those in the destination table. In a multi-table aggregation scenario, data writing through bypass import is not supported.
     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 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.

       • Modify 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; 
         

       • Modify the parameters of a user 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 if 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 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.
     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 perform the following operations:

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

   • Click Skip in the Actions column of the failed precheck item. In the dialog box that prompts the consequences of the 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.