Migrate incremental data from an OceanBase database in Oracle compatible mode to a MySQL database

Prerequisites

• The data transmission service has the privilege to access cloud resources. For more information, see Grant privileges to roles for data transmission.

• You have created database users dedicated for data migration for the source OceanBase database in Oracle compatible mode and the target MySQL database, and granted required privileges to the users. For more information, see Create a database user.

Limitations

• The data transmission service supports MySQL 5.5, 5.6, 5.7, and 8.0.

• The data transmission service does not support migrating tables without a primary key from an OceanBase database in Oracle compatible mode to a MySQL database.

• The data transmission service does not support triggers at the target when it is a database. If triggers exist, the data migration may fail.

• The data transmission service supports the migration of an object only when the following conditions are met: the database name, table name, and column name of the object are ASCII-encoded without special characters. The special characters are line breaks, spaces, and the following characters: . | " ' ` ( ) = ; / & \.

Considerations

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

• If you modify a unique index at the target, you must restart the data migration task to avoid data inconsistency.

• 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 at the target, if the data type of any column is not supported by the data transmission service, implicit data type conversion may occur at the target, which causes inconsistent column types between the source and target.

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

• If you selected only Incremental Synchronization when you created the data migration task, the data transmission service requires that the local incremental logs of the source database be retained for at least 48 hours.

• If the source or target contains table objects that differ only in letter cases, the data migration results may not be as expected due to case insensitivity in the source or target.

Supported source and target instance types

In the following table, OceanBase Database in Oracle compatible mode is referred to as OB_Oracle, which supports OceanBase cluster instances.

Procedure

1. Log on to the OceanBase Management Console and purchase a data migration task.

   For more information, see Purchase a data migration task.

2. On the Data Transmission > Data Migration page, click Configure for your new data migration task.

   

   To reference an existing task configuration, you can click Reference Configuration. For more information, see Reference a data migration task configuration.

3. On the Select Source and Target page, configure the parameters.

   Parameter	Description
   Migration Task 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.
   Source	If you have created an OceanBase data source in Oracle compatible mode, select it from the drop-down list. Otherwise, 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 OceanBase data source.
   Target	If you have created a MySQL data source, select it from the drop-down list. Otherwise, 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.
   Tag (Optional)	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 tasks.

4. Click Next. On the Select Migration Type page, specify migration types for the current data migration task.

   At present, only DML synchronization is supported for Incremental Synchronization. You can select operations as needed. For more information, see Configure DDL/DML synchronization.

   

5. Click Next. On the Select Migration Objects page, specify migration objects for the data migration task.

   You can select Specify Objects or Match Rules to specify the migration objects. This topic describes how to specify the migration objects by using Specify Objects. For information about matching rules, see Configure and modify matching rules.

   Important

   • The names of tables to be migrated, as well as the names of columns in the tables, must not contain Chinese characters.

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

   

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

   2. In the Source Object(s) list of the Specify Migration Scope section, select the objects to migrate. You can select tables and views of one or more databases.

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

   Data Transmission Service lets you import objects from text files. It also lets you rename destination objects, set row filters, view column information, and remove a single object or all objects.

   Note

   When you select migration objects using the Matching Rules method, the matching rule syntax overrides the renaming capability, and the Actions section is limited to setting filter conditions. For more information, see Configure and modify matching rules.

   Operation	Description
   Import Object	In the list on the right of the selection area, click Import Object in the upper-right corner. In the dialog box that appears, click OK. Important The import operation overwrites previous selections. Proceed with caution. In the Import Migration Objects dialog box, import the objects to be migrated. You can import a CSV file to rename database tables, set row filtering conditions, and perform other operations. For more information, see Download and import migration object configurations. Click Check Validity. After you import the migration objects, check their validity first. Column field mapping is not currently supported. After the check is passed, click OK.
   Rename	Data Transmission Service lets you rename migration objects. For more information, see Rename database and table objects.
   Settings	Data Transmission Service supports row filtering using WHERE conditions. For more information, see Filter data with SQL conditions. You can also view the column information of migration objects in the View Columns area.
   Remove/Remove All	Data Transmission Service lets you remove one or more objects that have been temporarily selected for the destination during data mapping. Remove a single migration object In the list on the right of the selection area, hover over the target object and click the displayed Remove button to remove the migration object. Remove all migration objects In the list on the right of the selection area, click Remove All in the upper-right corner. In the dialog box that appears, click OK to remove all migration objects.

6. Click Next. On the Migration Options page, configure the parameters for incremental synchronization.

   

   Parameter	Description
   Write Concurrency	The concurrency for writing data to the target during incremental synchronization. The maximum value is 512. A high write concurrency may incur excessive stress on the target, affecting the business.
   Incremental Synchronization Rate Limit	You can choose whether to limit the incremental synchronization rate as needed. If you choose to limit the incremental synchronization rate, you must specify the records per second (RPS) and bytes per second (BPS). The RPS specifies the maximum number of data rows synchronized to the target per second during incremental synchronization, and the BPS specifies the maximum amount of data in bytes synchronized to the target 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 and the instance specifications.
   Incremental Synchronization Start Timestamp	Specify a point in time after which data is to be synchronized. The default value is the current system time. For more information, see Set an incremental synchronization timestamp.

7. Click Precheck to precheck the data migration task.

   In the Precheck step, Data Transmission Service checks whether items meet the requirements, such as the read and write permissions of the database user and the network connectivity of the database. You can start the data migration task only after all check items pass. If the precheck fails:

   • You can identify and troubleshoot the problem, and then run the precheck again until it succeeds.

   • You can also click Skip in the Actions column for a failed precheck item. A dialog box appears that describes the impact of skipping this operation. To proceed, click OK.

8. After the precheck passes, click Start Task.

   If you do not want to start the task immediately, click Save. You can then start the task manually from the Data Migration Task List page or using batch operations. For more information about batch operations, see Batch Operations on Data Migration Tasks.

   Data Transmission Service lets you modify migration objects and their row filtering conditions while a data migration task is running. For more information, see View and modify migration objects and their filter conditions. After the data migration task starts, it performs the migration steps sequentially based on the selected migration types. For more information, see View migration details.

References

• Create an OceanBase data source

• Create a MySQL data source

• Configure and modify matching rules

• View details of a data migration task