Synchronize data from an IDB logical table to a MySQL-compatible tenant of OceanBase Database

OceanBase Migration Service (OMS) allows you to synchronize data from an IDB logical table to a MySQL-compatible tenant of OceanBase Database. This feature supports database and table sharding or database sharding only. This topic describes how to synchronize data from an IDB logical table to a MySQL-compatible tenant of OceanBase Database.

Limitations

• The IDB logical table must have a primary key and can be synchronized only to a MySQL-compatible tenant of OceanBase Database.

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

• OMS supports the synchronization 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: . | " ' ` ( ) = ; / & \.

Considerations

• If the clocks between nodes or between the client and the server are out of synchronization, the latency may be inaccurate during incremental synchronization.

  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 select only Incremental Synchronization when you create a data synchronization task, OMS requires that the local incremental logs in the source database be retained for more than 48 hours.

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

Supported DDL operations for synchronization and limitations

• Supported DDL operations for synchronization

  • ADD COLUMN: When you execute this statement, specify the default value in the statement.

  • MODIFY COLUMN: You can execute this statement only to increase the column length.

  Only two types of DDL statements executed on the logical table are automatically synchronized to the target table in the incremental synchronization stage. A DDL statement executed on any physical table is automatically synchronized to other tables. This DDL statement is not synchronized to other tables if it is executed later.

  Notice

  By default, a DDL statement executed on a logical table is synchronized to all physical tables. The execution of the statement does not cause the schemas in physical tables of the logical table to be different.

• Limitations

  • By default, schemas in a logical table are consistent. If they are inconsistent, DDL statements are executed only on some tables. Data synchronization fails because of inconsistent data.

  • Executing the ALTER TABLE MODIFY COLUMN statement does not work with the following case:

    A nullable column is set to a non-null column and the data is pulled back. In this case, data synchronization is likely to fail because the data is null but the constraint in the target database does not allow null values.

    To solve this issue, you can execute a DDL statement on the target column to allow null values in this column. The following MODIFY DDL statements are automatically synchronized.

Procedure

1. Create a data synchronization task.

   

   1. Log in to the OMS console.

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

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

2. On the Create Task page, specify the name of the synchronization 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. On the Select Source and Target page, configure the parameters.

   

   Parameter	Description
   Source	If you have created an IDB data source, select it from the drop-down list. If not, click New Data Source in the drop-down list to create one in the dialog box on the right side. For more information, see Create an IDB data source.
   Target	If you have created a MySQL data source of OceanBase Database, select it from the drop-down list. If not, click New Data Source in the drop-down list to create one in the dialog box on the right side. For more information, see Create a physical OceanBase data source.
   Tag (Optional)	Click the field 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 synchronization tasks.

4. Click Next. In the Select Synchronization Type step, specify the synchronization types for the current data synchronization task.

   The supported synchronization types are Full Synchronization and Incremental Synchronization. Incremental Synchronization supports the DML synchronization and DDL synchronization options. The supported DML operations are INSERT, DELETE, and UPDATE. Select the options as needed. For more information, see Configure DDL/DML synchronization.

   Notice

   If you want to perform Full Synchronization, set OBProxy URL, Full Synchronization User, and Full Synchronization Password when you add an IDB data source. Otherwise, this option is unavailable.

5. Click Next. In the Select Synchronization Objects step, select the objects to be synchronized in the current data synchronization task.

   1. Enter the global unique ID (GUID) of the IDB logical table in the GUID field.

   2. Select the objects to synchronize from the Source Object(s) list and click > to add them to the Target Object(s) list.

   OMS allows you to perform the following operations on the objects in the target database: rename objects, set sharding columns, and remove objects.

   Operation	Description
   Rename objects	OMS allows you to rename synchronized databases or tables. For more information, see Rename a migration or synchronization object.
   Configure settings	In the list on the right, move the pointer over the object that you want to set. Click Settings. In the Settings dialog box, click Sharding Columns and select the sharding columns that you want to use from the drop-down list. You can select multiple columns as sharding columns. This parameter is optional. Unless otherwise specified, select the primary key as sharding columns. If the primary key is not load-balanced, select load-balanced columns with unique identifiers as sharding columns to avoid potential performance issues. Sharding columns can be used for the following purposes: Load balancing: Threads used for sending messages can be recognized based on the sharding columns if the target table supports concurrent writes. Orderliness: OMS ensures that messages are received in order if the values of the sharding columns are the same. The orderliness specifies the sequence of executing DML statements for a column. Click OK.
   Remove one or all objects	OMS allows you to remove one or all objects to be synchronized to the target database during data mapping. To remove one synchronization object In the list on the right, move the pointer over the object that you want to remove, and click Remove to remove the synchronization object. Remove all synchronization objects In the list on the right, click Remove All in the upper-right corner. In the dialog box that appears, click OK to remove all synchronization objects.

6. Click Next. In the Synchronization Options step, configure the parameters.

   • Full synchronization

     The following parameters are displayed only if you have selected Full Synchronization in the Select Synchronization Type step.

     Parameter	Description
     Full Synchronization Rate Limit	You can choose whether to limit the full 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 full synchronization, and the BPS specifies the maximum amount of data in bytes synchronized to the target database per second during full synchronization. Note The RPS and BPS values specified here are only for throttling. The actual full synchronization performance is subject to factors such as the settings of the source and target databases and the instance specifications.
     Full Synchronization 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 synchronization. By setting the resource configuration for the Full-Import component, you can limit the resource consumption of a task in the full synchronization stage. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.

   • Incremental synchronization

     The following parameters are displayed only if you have selected Incremental Synchronization in the Select Synchronization 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 Synchronization as the synchronization type, the default value of this parameter is the task startup time and cannot be modified. If you did not select Full Synchronization as the synchronization type, set this parameter to a certain point in time, which is the current system time by default. For more information, see Set an incremental synchronization timestamp.

   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.

   

7. Click Precheck.

   During the Precheck stage, OMS checks whether all the physical tables in the logical table are accessible by using the username and password entered in ODP and whether the user has the SELECT privilege. In addition, OMS checks whether the obconfig_url parameter of OceanBase Database is correctly configured. You can run the show parameters like "obconfig_url" command in the sys tenant to obtain the value of obconfig_url for pulling logs in subsequent incremental synchronization.

   If an error is returned during the precheck, you can perform the following operations:

   • Identify and troubleshoot the problem 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.

8. 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.

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