Migrate data from a MySQL-compatible tenant of OceanBase Database to a MySQL database

This topic describes how to use OceanBase Migration Service (OMS) to migrate data from a MySQL-compatible tenant of OceanBase Database, which can be a physical data source, a public cloud OceanBase data source, or a standalone data source, to a MySQL database.

Background information

You can create a data migration task in the OMS console to seamlessly migrate the existing business data and incremental data from a MySQL-compatible tenant of OceanBase Database to a MySQL database through schema migration, full migration, and incremental synchronization.

MySQL databases in the following modes are supported as the sources: 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 created dedicated database users in the source MySQL-compatible tenant of OceanBase Database and the target MySQL database for data migration and granted the required privileges to the users. For more information, see Create a database user.

Limitations

• Limitations on the source database

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

• At present, OMS supports MySQL 5.5, 5.6, 5.7, and 8.0.

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

• OMS does not support a primary key or unique key that contains data of both the FLOAT and BINARY types.

• OMS does not support an index field greater than 16,000 bytes (or 4,000 characters) in length for MySQL 5.6.

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

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

• If temporary tables exist in the MySQL-compatible tenant of OceanBase Database of a version earlier than V4.0.0, full migration fails.

• 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 line breaks, spaces, and the following characters: . | " ' ` ( ) = ; / & \.

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

Considerations

• 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 Preparations.

• If the UTF-8 character set is used in the source database, we recommend that you use a compatible character set, such as UTF-8 or UTF-16, in the target database 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 increment.

  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.

• In a task for migrating data from a MySQL-compatible tenant of OceanBase Database of a version earlier than V3.2.x to a MySQL database, if the source table is a multi-partition table with a global unique index and you update the values of the partition key of the table, data may be lost during migration.

• If the value of the explicit_defaults_for_timestamp variable in the source database is different from that in the target database, inconsistent TIMESTAMP data may be detected during verification.

• When DDL synchronization is disabled, if you change the unique index in the target database, you must restart the Incr-Sync component. Otherwise, the data in the source and target databases may be inconsistent.

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

• OceanBase Database supports the timestamps ranging from 0000-00-00 00:00:00.000000 to 9999-12-31 23:59:59.999999 in the MySQL compatible mode, while a MySQL database supports the timestamps ranging from 1970-01-01 00:00:01.000000 to 2038-01-19 03:14:07.999999. When a timestamp not supported by the target database is written to the source database, OMS inserts this timestamp to the target database and writes it into the error.log file or the exception table.

• In multi-table aggregation scenarios:

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

  • We recommend that you manually create schemas in the target database. If you use OMS to create schemas, skip failed objects in the schema migration step.

• In a data migration task where the source is OceanBase Database and DDL synchronization is enabled, if a RENAME operation is performed on a table in the source database, we recommend that you restart the task to avoid data loss during incremental synchronization.

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

  • When you manually create a table schema in the target database, if the data types of any columns are not supported by OMS, implicit data type conversion may occur in the target database, which causes inconsistent column types between the source and target databases.

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

• In a data migration task where the source is OceanBase Database and DDL synchronization is enabled, if a RENAME operation is performed on a table in the source database, we recommend that you restart the task to avoid data loss during incremental synchronization.

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

  ​If you select Full Migration and Incremental Synchronization when you create the data migration task, OMS requires that the archive logs in the source database be retained for at least seven days. Otherwise, the data migration task may fail or the data in the source and target databases may be inconsistent because OMS cannot obtain incremental logs.

• If the source and target table objects differ only in capitalization of their names, the data migration result may not be as expected because the object names in the source or target database are case-insensitive.

• At present, the data migration task does not support tables without a non-null unique key. To avoid duplicate data in case of task restart and other exceptions, we recommend that you configure a non-null unique key for each table.

Data type mappings

Procedure

1. Create a data migration task.

   

   1. Log in to the OMS console.

   2. In the left-side navigation pane, click Data Migration.

   3. On the Data Migration page, click Create Task in the upper-right corner.

2. On the Create Task page, specify the name of the migration task.

   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 task name must be a unique identifier in the OMS system.

3. In the Select Source and Target step, configure the parameters.

   

   Parameter	Description
   Source	If you have created a data source for the MySQL compatible mode of OceanBase Database, which can be a physical data source, a public cloud OceanBase data source, or a standalone 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, Create a public cloud OceanBase data source, or Create a standalone OceanBase data source.
   Target	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 the parameters, see Create a MySQL data source. You can select a MySQL data source in primary database only mode or primary/standby databases mode. A MySQL data source in standby database only mode cannot serve as the target for data migration. This topic uses a data source in primary/standby databases mode as an example.
   Tag (Optional)	Click the text box and select a 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 tasks.

4. Click Next. At the Select Migration Type step, select Synchronization Topology as One-way Synchronization.

   OMS supports One-way Synchronization and Bidirectional Synchronization. This topic describes how to configure one-way synchronization. For more information about bidirectional synchronization, see Configure a bidirectional synchronization task.

5. In the Migration Options section, select the migration type for the current data migration task.

   

   The Options for Migration Type are Schema Migration, Full Migration, Incremental Synchronization, 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 target database. Temporary tables are automatically filtered out.
   Full migration	OMS migrates the existing data of tables in the source database to corresponding tables in the target database during a full migration task. If you select Full Migration, we recommend that you collect the statistics of the MySQL compatible mode of OceanBase Database before the data migration. For more information, see Manually collect statistics.
   Incremental synchronization	Changed data in the source database is synchronized to the corresponding tables in the target database after an incremental synchronization task starts. Supported data changes are data addition, modification, and deletion. Options for Incremental Synchronization are DML synchronization and DDL synchronization. Select the options as needed. For more information, see Configure DDL/DML synchronization. Incremental Synchronization has the following limitations: OceanBase Database V1.x does not support incremental synchronization. The standby MySQL database does not support incremental synchronization. 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 column to NULL. Otherwise, data migration may be interrupted. If you insert columns without data during incremental synchronization, the previous data will be padded based on the current time, causing time inconsistency.
   Reverse increment	When a reverse increment task starts, OMS migrates the data changed in the target database after the business switchover back to the source database in real time. Generally, incremental synchronization configurations are reused for reverse increment. You can also customize the configurations for reverse increment as needed. You cannot select Reverse Increment in the following cases: Multi-table aggregation is involved. Multiple source schemas map to the same target schema.

6. (Optional) Click Next.

   If you have selected Schema Migration or Incremental Synchronization without configuring the required parameters for the source MySQL compatible mode of OceanBase Database, the Add Data Source Information dialog box appears, prompting you to configure the parameters. For more information about the parameters, see Create a physical OceanBase data source, Create a public cloud OceanBase data source, or Create a standalone OceanBase data source.

   After you configure the parameters, click Test connectivity. After the test succeeds, click Save.

7. Click Next. In the Select Migration Objects step, select the objects that need to be migrated for the data migration task.

   You can select Specify Objects or Match by Rule to specify the migration objects. The following procedure describes how to specify migration objects by using the Specify Objects option. For information about the procedure for specifying migration objects by using the Match by Rule option, see Configure matching rules.

   Notice

   • If a database or table name contains double dollar signs ("$$"), you cannot create the migration task.

   • If you have selected DDL Synchronization in the Select Migration Type step, we recommend that you select Match by Rule to specify migration objects. This way, all new objects that meet the specified rules will be synchronized. If you select Specify Objects to specify migration objects, new or renamed objects will not be synchronized.

   • OMS automatically filters out unsupported tables. For information about the SQL statements for querying table objects, see SQL statements for querying table objects.

   

   1. In the Select Migration Objects section, select Specify Objects.

   2. In the Source Object(s) list, select the objects to be migrated. You can select tables and views of one or more databases as the migration objects.

   3. Click > to add the selected objects to the Target Object(s) list.

   OMS also allows you to import objects by using text, rename objects, configure row filters, select partitions and columns, and remove one or all objects to be migrated.

   Note

   When you select Match by Rule to specify migration objects, object renaming is implemented based on the syntax of the specified matching rules. In the operation area, you can only set filter conditions. For more information, see Configure matching rules.

   Operation	Steps
   Import objects	In the Target Object(s) list, 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 migration objects. For more information, see Rename a migration or synchronization object.
   Configure settings	OMS allows you to configure row filters, select partitions, and specify columns to be migrated. Hover the pointer over the target object in the right-side list of the selection area. Click Settings that appears. In the Settings dialog box, you can perform the following operations: In the Row Filters section, configure row filters by entering WHERE clauses of standard SQL statements. For more information, see Filter data by using SQL conditions. In the Partition section, select the specified partition data that you want to obtain in full migration. After you select a partition, click OK. In the Select Columns section, select the columns to be migrated. For more information, see Column filtering.
   Remove one or all objects	OMS allows you to remove one or all objects to be migrated to the target database during data mapping. To remove one migration object: In the Target Object(s) list, move the pointer over the target object and click Remove. To remove all migration objects: In the Target Object(s) list, click Remove All in the upper-right corner. In the dialog box that appears, click OK.

8. Click Next. In the Migration Options step, configure the parameters.

   • Schema Migration

     The following parameters are displayed only if you have selected One-way Synchronization > Schema Migration in the Select Migration Type step.

     

     Parameter	Description
     Automatically Enter Next Stage upon Completion	If you select schema migration and any other migration type, you can specify whether to automatically proceed to the next stage after schema migration is completed. The default value is Yes. You can also view and modify this value on the Schema Migration tab of the data migration task details page.
     Normal Index Migration Method	The migration method for non-unique key indexes associated with the migrated table objects, including Do Not Migrate, Migrate with Schema, and Post-Full-Migration (displayed only when Full Migration is selected).

   • Full migration

     The following parameters are displayed only if you have selected One-way Synchronization > Full Migration in the Select Migration Type step.

     

     Parameter	Description
     Full Migration Rate Limit	You can choose whether to limit the full migration rate as needed. If you choose to limit it, you must specify the RPS and BPS. The RPS specifies the maximum rows of data migrated to the target database per second during full migration, and the BPS specifies the maximum amount of data in bytes migrated to the target database per second during full migration. Note The RPS and BPS values specified here are only for throttling. The actual full migration performance is subject to factors such as the settings of the source and target databases and the instance specifications.
     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. By setting the resource configuration for the Full-Import component, you can limit the resource consumption of a task in the full migration phase. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.
     Handle Non-empty Tables in Target Database	Valid values: Ignore and Stop Migration. If you select Ignore, when the data to be inserted conflicts with the existing data of a target table, OMS retains the existing data and records the conflict data. If you select Stop Migration and a target table contains data, an error is returned during full migration, indicating that the migration is not allowed. In this case, you must clear the data in the target 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.

   • Incremental synchronization

     The following parameters are displayed only if you have selected One-way Synchronization > Incremental Synchronization in the Select Migration Type step.

     

     Parameter	Description
     Incremental Synchronization Rate Limit	You can choose whether to limit the incremental synchronization rate as needed. If you choose to limit it, you must specify the RPS and BPS. The RPS specifies the maximum rows of data synchronized to the target database per second during incremental synchronization, and the BPS specifies the maximum amount of data in bytes synchronized to the target database per second during incremental synchronization. Note The RPS and BPS values specified here are only for throttling. The actual incremental synchronization performance is subject to factors such as the settings of the source and target databases and the instance specifications.
     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. By setting the resource configuration for the Store component, you can limit the resource consumption of a task in log pull in the incremental synchronization stage. 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 writes. By setting the resource configuration for the Incr-Sync component, you can limit the resource consumption of a task in data writes in the incremental synchronization stage. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.
     Incremental Record Retention Duration	The duration that incremental parsed files are cached in OMS. A longer retention duration results in more disk space occupied by the Store component.
     Incremental Synchronization Start Timestamp	If you have selected Full Migration as the migration type, 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.

   • Reverse increment

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

     

     You can enable Adapt to the Online DDL tool for reverse increment from a MySQL-compatible tenant of OceanBase Database to a MySQL database. After you enable this feature, OMS allows you to use an online DDL tool to perform online schema changes. OMS filters out temporary table objects during data migration to improve the stability of data migration. For more information, see Online DDL tools.

   • Advanced options

     

     The following parameters are displayed only if the source is a MySQL-compatible tenant of OceanBase Database V4.3.0 or later and you have selected DDL synchronization for Reverse Increment in the Select Migration Type step.

     This parameter specifies the storage type for source table objects during reverse increment. The storage types supported for source table objects are Default, Row Storage, Column Storage, and Hybrid Row-Column Storage. For more information, see default_table_store_format.

     Note

     The value Default means that other parameters are automatically set based on the parameter configurations of the target database. New table objects created by reverse incremental DDL statements in reverse increment are written to corresponding schemas in reverse increment based on the specified storage type.

   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 task or component template.

   

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

   During the precheck, OMS checks the read and write privileges of the database users and the network connectivity of the databases. A data migration task 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 issue and then perform the precheck again.

   • Click Skip in the Actions column of a failed precheck item. In the dialog box that prompts the consequences of the operation, click OK.

10. Click Start Task. If you do not need to start the task now, click Save to go to the details page of the task. You can start the task later as needed.

You can click Configure Validation Task in the upper-right corner of the data migration details page to compare the data between the source and target databases. For more information, see Create a data validation task.

OMS allows you to modify the migration objects when the data migration task is running. For more information, see View and modify migration objects. After the data migration task is started, it is executed based on the selected migration types. For more information, see the View migration details section in View details of a data migration task.