Migrate data from a MySQL database to OceanBase Database Community Edition

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

Background information

You can create a data migration project in the console of OMS Community Edition to seamlessly migrate the existing business data and incremental data from a self-managed MySQL database to OceanBase Database Community Edition through schema migration, full migration, and incremental synchronization.

The MySQL 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 mode.

Prerequisites

• You have enabled binlogs for the self-managed MySQL database. For more information, see Enable binlogs for the MySQL database.

• You have created dedicated database users for data migration in the self-managed MySQL database that serves as the source and OceanBase Database Community Edition that serves as the destination, and granted the 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.

• OMS supports the following MySQL database versions: 5.5, 5.6, 5.7, and 8.0. OMS Community Edition supports only the MySQL InnoDB storage engine and is unavailable for other engines.

• The precheck fails if the primary key is data of the FLOAT or DOUBLE type. We recommend that you do not use data of these types as the primary key.

• 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 an index field greater than 767 bytes (or 191 characters) in length in MySQL databases.

• 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 . | " ' ` ( ) = ; / &

• If the lower_case_table_names settings of the source and destination are different, the project cannot be created. If lower_case_table_names is set to 0 in the source and destination databases, the source and destination databases are case sensitive. In this case, the project cannot be created either.

  By default, lower_table_case_names is set to 1 in the destination, and the destination database objects are created with lowercase names.

• OMS Community Edition does not support the migration of cascading foreign keys from the source MySQL database.

• The clock of the source database is synchronized with that of the destination database.

• In the reverse incremental data migration from a MySQL 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.

Considerations

• The host of the MySQL database must have sufficient outbound bandwidth. Insufficient outbound bandwidth on the host will slow down log parsing and data migration, which may increase the latency of data synchronization.

• 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 collations of the source and destination databases are different, a table whose primary key is data of the VARCHAR type fails the data consistency verification.

• If incremental parsing is required for the MySQL database, you must specify the ID of the MySQL server.

• 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.

• 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 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.

• OMS Community Edition supports data migration between tables that have different numbers of fields. If an error is reported because a field of the source table does not exist in the destination table during full migration or incremental synchronization, you can set the ignoreRedunantColumnsReplicate parameter of the Full-Import or Incr-Sync component to true and then resume the data migration project.

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 Migration Projects 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. Notice The project name must be unique in OMS Community Edition.
   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 MySQL 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 parameters, see Create a MySQL data source. Note If you select Allow OMS to automatically write heartbeat data into this instance during incremental synchronization. This resolves the problem of high latency when no business data is written in the source database. when you add a MySQL data source, OMS Community Edition will create and update the drc.heartbeat table in the corresponding MySQL database. In that case, the MySQL database user must have the privileges to create and write the table. For more information, see Create and update a heartbeat table. You can select a MySQL data source in primary database only mode or primary/standby databases mode. This topic describes how to create a data migration project with a MySQL data source in primary/standby databases mode.
   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.
   Scenario Type	Valid values: Tables with Unique Key and All Tables. If a table has primary key constraints or unique constraints, and fields in the table are unique, this table is a table with a unique key. If you select All Tables, tables that have unique and non-unique keys, except for temporary tables, are included.

3. Click Next.

   If you selected Tables with Unique Key for Scenario, click OK in the dialog box that appears.

4. 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. In a project that migrates schemas from a MySQL database to OceanBase Database Community Edition, the database that does not exist in the destination can be automatically created.
   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 MySQL 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 Incremental Synchronization are DML Synchronization and DDL Synchronization. You can select the options as needed. For more information about DDL synchronization, see Supported DDL operations in incremental migration from a MySQL database to OceanBase Community Edition and limitations. Incremental Synchronization has the following limitations: If you select Incremental Synchronization, you need to enable binlogs for the source MySQL database, and set binlog_row_image to full and binlog_format to row. If you select Incremental Synchronization, the binlogs of the MySQL database must be retained for at least 24 hours. Otherwise, the migration project may be interrupted and cannot be resumed because of the absence of binlogs. If you select DDL Synchronization, when you perform a DDL operation in the source database that cannot be synchronized by OMS Community Edition, 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	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. OMS Community Edition supports full data verification of only tables with a unique key.
   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.

5. (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.

6. 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.

     • Do not select a table named in the format of *_ghc.

     • 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 Community Edition also allows you to import objects from text, rename objects, set row filters, view column information, 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.
     Settings	OMS Community Edition allows you to filter rows by using WHERE conditions. 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	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.

     Notice

     Set Object Exclusion Rule to {database_name}.*_ghc.

7. Click Next.

   If you select All Tables for Scenario, click Next in the dialog box that appears.

8. On the Migration Options page, configure the 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.

   • Schema migration

     This section is displayed only when you have selected Schema Migration on the Select Migration Type page. You can specify the Character Set Mapping and Collation Mapping parameters as needed.

   • 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.