Migrate data in active-active disaster recovery scenarios

OceanBase Migration Service (OMS) Community Edition allows you to migrate data between OceanBase Database Community Edition and MySQL databases, and between tenants of OceanBase Database Community Edition in active-active disaster recovery scenarios.

Background information

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

At present, OMS Community Edition supports the following types of data migration tasks in active-active disaster recovery scenarios: migrate data from a MySQL database to OceanBase Database Community Edition and migrate data between tenants of OceanBase Database Community Edition. OMS Community Edition 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 task to synchronize data in real time between the primary and standby IDCs based on OMS Community Edition. 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 Community Edition provides an active-active solution to allow two IDCs to share business traffic. An active-active solution involves two databases. An application writes data to both databases based on the specified rules, and both databases retain all data of the application. In a non-active-active scenario, an application writes data only to one database. In other words, data written to one database will not be written to the other database.

Prerequisites

• You have created a corresponding schema in the target database. OMS Community Edition allows you to migrate tables and columns. You must create a corresponding schema in the target database before the migration.

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

Limitations

• Take note of the following 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.

• Active-active disaster recovery between tenants of OceanBase Database Community Edition supports the migration of only tables with unique keys.

• You cannot add migration objects to or remove migration objects from a task in an active-active disaster recovery scenario when the task is running.

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

• When useTargetIndex is set to false in incremental synchronization, if the target tenant uses a column 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 column of the BINARY type in the target tenant, the UPDATE or DELETE operation cannot match data. This causes data quality risks.

• The data source identifiers and user accounts must be globally unique in OMS Community Edition.

• OMS Community Edition supports the migration of only objects whose database name, table name, and column name are ASCII-encoded without special characters. The special characters are line breaks and | " ' ` ( ) = ; / &.

• If temporary tables exist in OceanBase Database Community Edition of a version earlier than V4.0.0, full migration fails.

• The source cannot be a standby OceanBase database.

Considerations

• To ensure the performance of a data migration task, we recommend that you migrate no more than 1,000 tables at a time.

• If you use OceanBase Database Community Edition V4.x, we recommend that you enable log archiving. If log archiving is enabled, OMS Community Edition implements incremental synchronization by consuming archive logs after clogs are recycled. For more information about how to enable log archiving, see the Log archive chapter.

• If the UTF-8 character set is used in the source, we recommend that you use a compatible character set, such as UTF-8 or UTF-16, in 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 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 active-active disaster recovery scenarios from a tenant of OceanBase Database Community Edition of a version earlier than V3.2.x to a MySQL database or another tenant of OceanBase Database Community Edition of a version earlier than V3.2.x, if a source table is a multi-partition table with a global unique index and the values of the partitioning key of the table are updated, data can be lost during the migration.

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

• 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 if you want to perform data merge migration:

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

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

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

• By default, lower_case_table_names is set to 1 in the target database, 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, if the data type of a column in the source is not supported by OMS Community Edition, implicit data type conversion may occur, 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.

• If you select only Incremental Synchronization when you create the data migration task, OMS Community Edition requires that the local incremental 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 Community Edition requires that the local incremental logs of 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 Community Edition cannot obtain incremental logs.

• If the binlog_row_image value is not FULL when the application starts, you can set it to FULL. After that, you must restart the application. Otherwise, OceanBase Community Edition will lack log information, which leads to issues with data synchronization. The command for setting the value is as follows:

  set global binlog_row_image = 'FULL';
  

Procedure

1. Create a data migration task.

   1. Log in to the console of OMS Community Edition.

   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.
   Tag	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 migration tasks.
   Source/Target	If you have created a 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 of a data source, see corresponding topics in the Create data sources chapter. Active-active disaster recovery scenarios are supported for data migration tasks between a MySQL database and OceanBase Database Community Edition.
   Scenarios	Two scenarios are available: Data Migration and Active-Active Disaster Recovery . In this example, select Active-Active Disaster Recovery . If the target is an OceanBase data source deployed on a public cloud, you cannot select Active-Active Disaster Recovery .
   Scenario Type	This parameter is available only when you migrate data from a MySQL database to OceanBase Database Community Edition. Valid values: Tables with Unique Key and All Tables . ​If a table has a primary key or non-null unique key, this table is a table with a unique key. If you select All Tables , tables with a primary key or a unique key and those without a unique key, except for temporary tables, are included. If you select Active-Active Disaster Recovery for Scenarios , you can migrate only tables with a unique key.

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

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

   Options for Migration Type are 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. In a task that migrates schemas from a MySQL database to OceanBase Database Community Edition, the database that does not exist in the target can be automatically created.
   Full migration	After a full migration task is started, OMS Community Edition 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 database before the data migration.
   Incremental synchronization	Changed data in the source database is synchronized to the corresponding tables in the target database after an incremental synchronization task starts. Data changes are data addition, modification, and deletion. Options for Incremental Synchronization are DML Synchronization and DDL Synchronization. You can select the options as needed. For more information about DDL operations, see Supported DDL operations for synchronization and limitations.
   Full verification	After the full migration and incremental synchronization are completed, OMS Community Edition 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 databases before full verification. For more information about how to collect statistics of OceanBase Database Community Edition, see Manual statistics collection. If you select Incremental Synchronization but do not select all DML operations in the DML Synchronization section, you cannot select Full Verification . OMS Community Edition supports full verification only for tables with a primary key or a non-null unique key.

5. (Optional) Click Next .

   If you have selected Schema Migration or Incremental Synchronization without configuring the required parameters for the source OceanBase Database, the More About Data Sources dialog box appears to prompt you to configure the parameters. For more information about the parameters, see Create an OceanBase-CE data source.

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

   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 for migration objects.

   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 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.

   • When you migrate data from a MySQL database to OceanBase Database Community Edition, do not select a table named in the "*_ghc" format.

   • When you migrate data from a MySQL database to OceanBase Database Community Edition, do not select tables named in the "*_ghc" format if you choose the Specify Objects option, and make sure that you set Object Exclusion Rule to {database_name}.*_ghc if you choose the Match Rules option.

   OMS Community Edition also allows you to import objects from text, rename objects, set row filters, view column information, and remove a single migration object or all migration objects.

   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 Community Edition allows you to rename migration objects. For more information, see Rename a database table.
   Configure settings	OMS Community Edition 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 Community Edition 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 parameters.

   To view or modify parameters of the Full-Import or Incr-Sync component, click Configuration Details in the upper-right corner of the Full Migration or Incremental Synchronization section. For more information about the parameters, see Component parameters.

   • Schema migration

     The following parameters are displayed only if you have selected Schema Migration on the Select Migration Type page. You can configure the Character Set Mapping and Collation Mapping parameters as needed.

   • Full migration

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

     Parameter	Description
     Concurrency Speed	Valid values: Stable , Normal , Fast , and Custom . The amount of resources to be consumed by a full migration task varies based on the migration performance. If you select Custom , you can set Read Concurrency , Write Concurrency , and JVM Memory as needed.
     Processing Strategy When Target Table Has Records	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 Community Edition 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 contains more data than the source 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 Community Edition ignores this error and continues to migrate data. Proceed with caution.
     Writing Method	Valid values: SQL (specifies to write data to tables by using INSERT or REPLACE) and Direct Load (specifies to write data through direct load). For more information about the direct load method, see Direct load.
     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.

     If post-indexing is allowed, we recommend that you adjust the parameters based on the hardware conditions of the target database and the business traffic.

     • If you use OceanBase Database Community Edition V4.x, adjust the following parameters of the sys tenant and business tenants by using a command-line interface (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 Community Edition 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
     Concurrency Speed	Valid values: Stable , Normal , Fast , and Custom . The amount of resources to be consumed by an incremental synchronization task varies based on the synchronization performance. If you select Custom , you can set Read Concurrency , Write Concurrency , and JVM Memory as needed.
     Incremental Synchronization Start Timestamp	If you have set the migration type to Full Migration , 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.
     Incremental Record Retention Time	The duration that incremental parsed files are cached in OMS Community Edition. A longer retention period results in more disk space occupied by the Store component of OMS Community Edition.

   • Full verification

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

     Parameter	Description
     Concurrency Speed	Valid values: Stable , Normal , Fast , and Custom . Through resource configuration for the Full-Verification component, you can limit the resource consumption of a task in the full verification phase. If you select Custom , you can set Read Concurrency , Write Concurrency , and JVM Memory as needed.

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

   During the precheck, OMS Community Edition 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 problem and then perform the precheck again.

   • Click Skip in the Actions column of the 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.

   After the data migration task is started, it is executed based on the selected migration types. For more information, see the Migration Details section in the View details of a data migration task topic.

   Notice

   When you execute a data migration task in an active-active disaster recovery scenario, take note of the following considerations:

   • Forward switchover is not supported.

   • OMS Community Edition automatically starts reverse incremental synchronization before full verification based on the settings of incremental synchronization.

References

• Create an OceanBase-CE data source

• Component parameters

• View and modify migration objects

• View details of a data migration task