Create an active-active disaster recovery task in OceanBase Database

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

Background information

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

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 use OMS to create a task to synchronize data in real time between the primary and standby IDCs. When the primary IDC encounters a disaster or is down, 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 target OceanBase database.

• You have created dedicated database users for data migration in the source and target OceanBase databases and granted 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.

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

  Specifically, you can migrate data between MySQL-compatible tenants or between Oracle-compatible tenants.

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

• When you create an active-active disaster recovery task, you cannot select reverse increment.

• OMS does not support the migration of data from OceanBase Database V1.4.x to OceanBase Database V4.x.

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

• When you migrate data from OceanBase Database V1.4.79, OMS supports only OceanBase Database V2.2.77 or later as the target. When you migrate data from OceanBase Database V2.1.0 or later, OMS supports OceanBase Database of the same version or a different version as the target.

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

• When useTargetIndex is set to false in incremental synchronization, if the target tenant uses a field of the BINARY type as the primary key or unique key, and the length of the data in the source tenant is different from the length of the field of the BINARY type in the target tenant, the UPDATE or DELETE operation cannot match data. This causes data quality risks.

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

• 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: . | " ' ` ( ) = ; / & \.

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

• 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.

  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 an active-active disaster recovery task in OceanBase Database of a version earlier than V3.2.x, if the source table is a multi-partition table with a global unique index and you update the values of the partitioning key of the table, data may be lost during migration.

• 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.

• 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.

• Take note of the following considerations in a scenario where database or table aggregation is enabled:

  • 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.

• 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.

• Take note of the following limitations on MySQL-compatible tenants of OceanBase Database:

  • For data migration between MySQL-compatible tenants of OceanBase Database, the default value of the lower_case_table_names parameter for the target tenant is 1, and the target database objects are created with lowercase names.

  • 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.

• Take note of the following limitations on Oracle-compatible tenants of OceanBase Database:

  • A table containing a primary key or a non-null unique key, which must not be a function-based unique key, is considered a table with a primary key.

    ​If the source OceanBase database is of a version earlier than V2.2.77 or a source table contains a function-based unique key on a virtual column, OMS may fail to accurately identify whether the table contains a function-based unique key, which may lead to misjudgment of the table with a primary key. This may slow down full migration and full verification and cause data inconsistency in incremental synchronization.

  • In an Oracle-compatible tenant of OceanBase Database V2.2.76 or earlier, the ALL_TABLES view may mistake partitioned tables for non-partitioned tables. As a result, OMS may read incorrect data from the view. In this case, manually create this table in the target database. For more information, see Create a partitioned table.

  • If you skip the "source-primary-database ROW_MOVEMENT check" precheck item during the migration, data inconsistency is expected during the synchronization of a table whose ROW_MOVEMENT value is enable.

• 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 7 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.

Create a forward link

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 New Task in the upper-right corner.

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

   Parameter	Description
   Data 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, which can be a physical data source or a public cloud 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 or Create a public cloud OceanBase data source.
   Target	If you have created an OceanBase data source, which can be a physical data source or a public cloud 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.
   Scenarios	Two scenarios are available: Data Migration and Active-Active Disaster Recovery. In this example, select Active-Active Disaster Recovery. Notice The source and target data sources must be tenants of the same type in OceanBase Database. The source and target nodes must belong to different regions.
   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.

3. Click Next. In the dialog box that appears, click OK.

   Note that this task supports only tables and views with a primary key or a non-null unique index and those without are automatically filtered out.

   

4. On the Select Migration Type page, configure the parameters.

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

   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	After a full migration task is started, OMS migrates existing data of tables in the source database to corresponding tables in the target database. If you select Full Migration, we recommend that you collect the statistics of the source OceanBase Database before the data migration. For more information, see Manual statistics collection.
   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 based on your business needs. For more information, see Configure DDL/DML synchronization. Incremental Synchronization has the following limitations: You can enable DDL synchronization in either the forward or reverse link. 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.
   Full verification	After the full migration and incremental synchronization are completed, OMS automatically initiates a full verification task to verify the data tables in the source and target databases. If you select Full Verification, we recommend that you collect the statistics of both the source and target OceanBase databases before full verification. If you have selected Incremental Synchronization but did not select all DML statements in the DML Synchronization section, OMS does not support full verification.

5. (Optional) Click Next.

   If you have selected Schema Migration or Incremental Synchronization without configuring the required parameters for the source 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 or Create a public cloud OceanBase data source.

   After you configure the parameters, click Test Connection. After the test succeeds, click OK.

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. 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 Rules option, see Configure matching rules.

   Notice

   • 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.

   • If you have selected DDL Synchronization in the Select Migration Type step, we recommend that you select Match Rules 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 Specify Migration Scope section, select the objects to be migrated from the Source Object(s) list. 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 from text, rename objects, set row filters, view column information, and remove a single object or all objects to be migrated.

   Note

   When you select Match Rules 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	Description
   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 objects	OMS allows you to rename migration objects. For more information, see Rename a migration or synchronization object.
   Configure settings	OMS 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 objects in the View Column section.
   Remove one or all objects	OMS allows you to remove a single object or all objects to be migrated to the target database during data mapping. To remove a single migration object: In the list on the right of the Specify Migration Scope section, move 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.

7. Click Next. On the Migration Options page, configure the following parameters.

   • Full migration

     The following parameters are displayed only if you have selected Full Migration on the Select Migration Type page.

     

     Parameter	Description
     Full Migration Rate Limit	You can choose whether to limit the full migration rate as needed. If you choose to limit the full migration rate, you must specify the records per second (RPS) and bytes per second (BPS). The RPS specifies the maximum number of data rows 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. Through resource configuration for the Full-Import component, you can limit the resource consumption of a task in the full migration stage. 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 are 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. Notice If you select Ignore, data is pulled in IN mode for full verification. In this case, the scenario where the target table contains more data than the source table cannot be verified, and the verification efficiency will be decreased. 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.
     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 if you have selected 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. OceanBase Database V1.x does not support the post-indexing feature.

     If post-indexing is allowed, we recommend that you adjust the parameters based on the hardware conditions of your OceanBase Database and the current business traffic.

     • If you use OceanBase Database V4.x, adjust the following parameters of the sys tenant and business tenants by using a 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 V2.x or 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 parameters are displayed only if you have selected Incremental Synchronization on the Select Migration Type page.

     

     Parameter	Description
     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 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. Through 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. Through 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 Time	The duration that incremental parsed files are cached in OMS. A longer retention period 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.

   • Full verification

     The following parameters are displayed only if you have selected Full Verification on the Select Migration Type page.

     

     Parameter

     Description

     Full Verification Resource Configuration

     You can select Small, Medium, or Large to use the corresponding default values of Read Concurrency and Memory. You can also customize the resource configurations for full verification. Through resource configuration for the Full-Verification component, you can limit the resource consumption of a task in the full verification stage. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.

   • Advanced options

     

     Parameter	Description
     Add Hidden Columns for Tables Without Non-null Unique Keys	This parameter is displayed only if you create a task to migrate data between two MySQL-compatible tenants of OceanBase Database and the source or target is a public cloud OceanBase data source for which you have selected OceanBase BinlogService as the incremental synchronization mode. At present, you can select only No.
     Target Table Storage Type	This section is displayed only if the target is OceanBase Database V4.3.0 or later and you have selected Schema Migration or DDL Synchronization for Incremental Synchronization on the Select Migration Type page. This parameter specifies the storage type for target table objects during schema migration or incremental synchronization. The storage types supported for target table objects are Default, Row storage, Column storage, and Hybrid columnar 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. Table objects in schema migration and new table objects created by incremental DDL statements are written to corresponding schemas based on the specified storage type.
     Source Table Storage Type	This section is displayed only if the source is OceanBase Database V4.3.0 or later and you have selected DDL Synchronization for Reverse Increment on the Select Migration Type page. 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 columnar 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 incremental DDL statements 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.

   

8. 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.

9. 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 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.

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 Task in the upper-right corner.

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

3. Click Next. In the dialog box that appears, click OK.

   Note that this task supports only tables and views with a primary key or a non-null unique index and those without are automatically filtered out.

4. On the Select Migration Type page, configure the parameters.

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

   Notice

   You can enable DDL synchronization in either the forward or reverse link.

5. (Optional) Click Next.

   If you have selected Incremental Synchronization without configuring the required parameters for the source 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 or Create a public cloud OceanBase data source.

   After you configure the parameters, click Test Connection. After the test succeeds, click OK.

6. 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 objects, set row filters, view column information, and remove one or all objects to be migrated. For more information, see the Create a forward link section.

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

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

9. Click Start Task to start incremental synchronization for the task.