Create an active-active disaster recovery project in OceanBase Database

OceanBase Migration Service (OMS) allows you to migrate data between the same type of tenants in OceanBase Database across regions and create active-active disaster recovery projects.

Background

As more users apply OMS in data migration, OMS must adapt to increasingly diverse scenarios. In addition to single-region data migration and data synchronization, OMS supports data migration across regions and active-active data synchronization between remote cities.

OMS supports the following active-active disaster recovery scenarios:

• Local data migration and synchronization

• Local primary/standby disaster recovery

• Local active-active disaster recovery

• Remote data migration and synchronization

• Remote primary/standby disaster recovery

• Remote active-active disaster recovery

Primary/standby disaster recovery is common in scenarios with data disaster recovery requirements. You can create a real-time synchronization link between the primary and standby IDCs based on OMS. When the primary IDC encounters disasters or downtime, the business can be switched to the standby IDC to avoid business interruption.

However, primary/standby disaster recovery causes a waste of resources in the standby IDC. Therefore, OMS provides an active-active solution to allow two IDCs to share business traffic.

When you migrate data between tenants of OceanBase Database in an active-active disaster recovery scenario, no forward switchover is performed, and you can enable DDL parameters only for one link.

Prerequisites

• You have created a corresponding schema in the destination tenant of OceanBase Database. OMS allows you to migrate tables and columns. Therefore, you must create a corresponding schema in the destination database before migration.

• You have created dedicated database users for data migration in the source and destination OceanBase databases and granted the corresponding privileges to the users. For more information, see Create a database user.

Limits

• You can migrate data only between tenants of the same mode in OceanBase Database.

  Specifically, you can migrate data from a MySQL tenant to another MySQL tenant, or from an Oracle tenant to another Oracle tenant.

• In an active-active disaster recovery project between MySQL tenants of OceanBase Database, only tables with unique keys can be migrated.

• When you create an active-active disaster recovery project, you cannot select reverse incremental migration.

• In long-term synchronization between databases, OMS does not support triggers in the destination database.

• If you enable DDL operations for incremental data migration, the drop index command is executed on all indexes, which may cause index loss in the destination database.

• You can migrate multiple schemas in a data migration project. The migration granularity ranges from a table to a tenant.

• You can migrate data from OceanBase Database V2.1.0 or later versions. The source and destination tenants can be created in different versions of OceanBase Database.

• If the character set used by the source database is UTF-8, we recommend that you use UTF-8 or a greater character set for the destination database.

• When you migrate data from OceanBase Database V1.4.x, OMS does not support primary keys that contain data of the FLOAT or DOUBLE type.

• You must create a forward link and a reverse link to form an active-active disaster recovery link, which does not support triggers.

• You can enable synchronization of DDL operations for incremental migration in either the forward or reverse link.

• A table containing a primary key or a not-null unique key but not a function-based unique key is a table with a primary key. If a table in the source Oracle tenant of OceanBase Database contains a function-based unique key in a virtual column, or if the database version is earlier than V2.2.77, OMS cannot accurately identify whether the table contains a function-based unique key and therefore may be inaccurate in determining whether the table has a primary key. This may slow down full migration and full verification and result in data inconsistency in incremental synchronization.

  During incremental synchronization, OMS processes data in parallel based on their UNIQUE constraints. If a table contains function-based unique keys,`` the related transaction operations must be performed in sequence during incremental synchronization. Otherwise, data inconsistency may occur.

• In an active-active disaster recovery project in OceanBase Database, when the database is of a version earlier than V3.2.x and contains a multi-partition table that has global unique indexes, if you update the value of a partitioning key of the table, data may be lost during migration.

• When you migrate data from one MySQL tenant of OceanBase Database to another, if the length of a field in the destination database is shorter than that in the source database, the data of this field will be truncated in the destination database, causing data inconsistency between the source and destination databases.

• If you change the unique index of the destination, you must restart the incremental synchronization. Otherwise, the data may be inconsistent.

Create a forward link

1. Create a data migration project.

   1. Log on to the OMS console.

   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 Chinese characters, digits, and letters. It must not contain any spaces and cannot exceed 64 characters in length.
   Label	Click the field and select the target tag from the drop-down list. You can 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 an OceanBase data source, select it from the drop-down list. If you have not created a data source, click Create Data Source in the drop-down list and create a data source in the dialog box that appears on the right. For more information, see Create OceanBase Database physical tables as a data source.
   Destination	If you have created an OceanBase data source, select it from the drop-down list. If you have not created a data source, click Create Data Source in the drop-down list and create a data source in the dialog box that appears on the right.
   Scenarios	Two scenarios are available: Data Migration and Active-Active Disaster Recovery. Select Active-Active Disaster Recovery. Notice The source and destination data sources must be the same type of tenants in OceanBase Database. The source and destination nodes must belong to different regions.

3. Click Next.

4. In the dialog box that appears, click OK.

   Note that this project supports only tables with a primary key or a non-null unique index and other tables and views are automatically filtered out.

5. On the Select Migration Type page, specify related parameters.

   ****Migration types available for the forward link include Schema Migration, Full Migration, Incremental Synchronization, and Full Verification.

   Migration type	Limits
   Full Migration	If you select Full Migration, we recommend that you collect the statistics of the source OceanBase database before the data migration.
   Incremental Synchronization	Options for Incremental Synchronization are DML Synchronization and DDL Synchronization. The DML operations for synchronization are Insert, Delete, and Update. You can select the operations as needed. For more information about supported DDL operations, see Supported DDL operations for incremental migration and limits. Incremental Synchronization has the following limits: You can enable synchronization of DDL operations for incremental migration in either the forward or reverse link. If you do not select DDL Synchronization, ensure that the source database involves no modifications and that the incremental DML data has been synchronized to the destination before DDL modifications. Then, perform related DDL operations in the source and destination databases respectively. If you have selected DDL Synchronization, when you perform a DDL operation for incremental migration that is not supported by OMS in the source database, data migration may fail. If you do not select DDL Synchronization, for DDL operations on tables in the migration link, perform these operations in the destination database first. Otherwise, data migration may fail.
   Full Verification	If you select Full Verification, we recommend that you collect the statistics of both the source and destination OceanBase databases before full verification. If you have selected Incremental Synchronization but did not select all DML statements in DML Synchronization, OMS does not support full data verification in this scenario.

6. (Optional) Click Next.

   Specify the related information for the source OceanBase database.

   • For incremental synchronization, specify the ConfigUrl, username, and password.

   • For schema migration, specify the username and password.

   • For the migration of a table without a unique key, specify the password of _OCEANBASE_INNER_DRC_USER.

   If you select Scheme Migration or Incremental Synchronization but no related parameters are configured for the data source of the source database, the More about Data Sources dialog box appears, prompting you to configure related parameters. For more information, see Create OceanBase Database physical tables as a data source.

   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 one of the following two modes to migrate objects: Specify Objects or Match Rules. If you select DDL Synchronization, only the Match Rules option is available.

   • 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 name of a table to be migrated and the names of columns in the table must not contain Chinese characters.

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

     When you migrate data between OceanBase databases, OMS allows you to import objects through text, rename object names, set row filters, view column information, and remove a single object or all objects to be migrated.

     Operation	Steps
     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	In the list on the right of the Specify Migration Scope section, hover the pointer over the target object. Click Rename. Enter a new name and click OK.
     Settings	OMS allows you to set WHERE conditions to filter data by row and view column information. In the list on the right of the Specify Migration Scope section, hover the pointer over the target object. Click Settings. In the Settings dialog box, specify a standard SQL WHERE clause to filter data by row. The setting takes effect for full migration and incremental synchronization. Notice Add an escape character (`) for column names. Example: `col`. Only the data meeting the WHERE condition is synchronized to the destination data source, thereby filtering data by row. If row-based filtering with the WHERE clause is enabled, right-trim is forcibly performed on data of the CHAR or VARCHAR type, which may cause an inaccurate comparison of the VARCHAR data. Proceed with caution. Click OK. You can also view column information of the migration object in the View Columns section.
     Remove/Remove All	OMS allows you to remove one or more objects from the destination database during data mapping. 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. The migration object is removed. 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 to remove all migration objects.

   • Select Match Rules. For more information, see Configure matching rules for migration objects.

8. Click Next. On the Migration Options page, configure the parameters.

   Parameter	Description
   Concurrency for Full Migration	The value can be Smooth, Normal, or Fast. The amount of resources to be consumed by a full data migration task varies based on the migration performance. You can also modify the configurations of the checker component to customize the concurrency. Notice To enable this feature, select Full Migration on the Select Migration Type page.
   Full Verification Concurrency	The value can be Smooth, Normal, or Fast. Different quantities of resources of the source and destination databases are consumed at different concurrencies. You can also modify the configurations of the checker component to customize the concurrency.
   Incremental Record Retention Time	The duration that incremental parsed files are cached in OMS. A longer retention period indicates more disk space occupied by the store component of OMS.
   Whether to Allow Destination Table to Be Not Empty During Full Migration	If destination tables are allowed to be not empty during full migration, full verification is performed in IN mode. Notice To enable this feature, select Full Migration on the Select Migration Type page.
   Whether to Allow Post-indexing	You can specify whether to allow post-indexing after full migration is completed. Post-indexing can shorten the time of full migration. Notice To enable this feature, select both Schema Migration and Full Migration on the Select Migration Type page. Only non-unique key indexes can be created after the migration is completed.

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

   During the precheck****, OMS checks the read and write privileges of the database users and the network connections of the databases. The data migration project can be started only after it passes all check items. If an error is returned:

   • You can troubleshoot the error and run the precheck again.

   • You can also click Skip in the Actions column of the precheck item that returns the error. Then, a dialog box appears, indicating the impact that may be caused if you choose to skip this check item. If you want to continue, click OK in the dialog box.

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 allows you to modify migration objects when a data migration project is running. For more information, see View and modify migration objects. After a data migration project is started, the migration objects will be executed based on the selected migration type. For more information, see the "View migration details" section in the View details of a data migration project.

Create a reverse link

You can create a reverse link only after the schema migration task on the forward link is completed.

1. 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.

3. Click Next.

4. In the dialog box that appears, click OK.

   Note that this project supports only tables with a primary key or a non-null unique index and other tables are automatically filtered out.

5. On the Select Migration Type page, specify related parameters.

   For the reverse link, set Migration Type to Incremental Synchronization.

   Notice

   You can enable synchronization of DDL operations for incremental migration in either the forward or reverse link.

6. (Optional) Click Next.

   For incremental synchronization, specify the ConfigUrl, username, and password of the source database. For the migration of a table without a unique key, you need to specify the password of _OCEANBASE_INNER_DRC_USER.

   If no related parameters are configured for the source database, the More about Data Sources dialog box appears, prompting you to configure related parameters. For more information, see Create OceanBase Database physical tables as a data source.

   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.

   When you create a reverse link, OMS also allows you to import objects through text, rename object names, set row filters, view column information, and remove one or all objects to be migrated. For more information, see the section that describes how to create a forward link.

8. Click Next. On the Migration Options page, configure the parameters.

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

10. Click Start Project to start the incremental synchronization task for the project.